Snort 3 User Manual

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Snort 3 User Manual i
Snort 3 User Manual
Snort 3 User Manual ii
REVISION HISTORY
NUMBER DATE DESCRIPTION NAME
Snort 3 User Manual iii
Contents
1 Overview 1
1.1 First Steps ....................................................... 2
1.2 Configuration ..................................................... 3
1.2.1 Environment ................................................. 4
1.2.2 Command Line ................................................ 4
1.2.3 Configuration File .............................................. 4
1.2.4 Rules ..................................................... 5
1.2.5 Converting Your 2.X Configuration ..................................... 5
1.3 Output ......................................................... 6
1.3.1 Basic Statistics ................................................ 6
1.3.2 Alerts ..................................................... 6
1.3.3 Files and Paths ................................................ 6
1.3.4 Performance Statistics ............................................ 7
2 Concepts 7
2.1 Terminology ...................................................... 7
2.2 Modules ........................................................ 8
2.3 Parameters ....................................................... 9
2.4 Plugins ........................................................ 10
2.5 Operation ....................................................... 10
2.5.1 Snort 2 Processing .............................................. 11
2.5.2 Snort 3 Processing .............................................. 11
2.6 Rules ......................................................... 11
2.7 Pattern Matching ................................................... 12
2.7.1 Rule Groups ................................................. 12
2.7.2 Fast Patterns ................................................. 13
2.7.3 Rule Evaluation ................................................ 13
3 Tutorial 13
3.1 Dependencies ..................................................... 13
3.2 Building ........................................................ 14
3.3 Running ........................................................ 15
3.4 Tips .......................................................... 15
3.5 Help .......................................................... 17
3.6 Common Errors .................................................... 17
3.7 Gotchas ........................................................ 18
Snort 3 User Manual iv
4 Usage 19
4.1 Environment ...................................................... 19
4.2 Help .......................................................... 19
4.3 Sniffing and Logging ................................................. 20
4.4 Configuration ..................................................... 20
4.5 IDS mode ....................................................... 21
4.6 Plugins ........................................................ 21
4.7 Output Files ...................................................... 22
4.8 DAQ Alternatives ................................................... 22
4.9 Logger Alternatives .................................................. 23
4.10 Shell .......................................................... 23
4.11 Signals ......................................................... 23
5 Features 24
5.1 AppId ......................................................... 24
5.1.1 Overview ................................................... 24
5.1.2 Dependency Requirements .......................................... 24
5.1.3 Configuration ................................................. 25
5.1.4 Session Application Identifiers ........................................ 26
5.1.5 AppId Usage Statistics ............................................ 26
5.1.6 Open Detector Package (ODP) Installation ................................. 26
5.1.7 User Created Application Detectors ..................................... 27
5.1.8 Application Detector Creation Tool ..................................... 27
5.2 Binder ......................................................... 28
5.3 Byte rule options ................................................... 28
5.3.1 byte_test ................................................... 28
Examples ................................................... 29
5.3.2 byte_jump .................................................. 29
Examples ................................................... 29
5.3.3 byte_extract .................................................. 29
Other options which use byte_extract variables ............................... 29
Examples ................................................... 30
5.3.4 byte_math ................................................... 30
Examples ................................................... 30
5.3.5 Testing Numerical Values .......................................... 30
5.4 DCE Inspectors .................................................... 33
5.4.1 Overview ................................................... 33
5.4.2 Quick Guide ................................................. 33
5.4.3 Target Based ................................................. 34
Snort 3 User Manual v
5.4.4 Reassembling ................................................. 34
5.4.5 SMB ..................................................... 35
Finger Print Policy .............................................. 35
File Inspection ................................................ 35
5.4.6 TCP ...................................................... 36
5.4.7 UDP ..................................................... 36
5.4.8 Rule Options ................................................. 36
dce_iface ................................................... 36
dce_opnum .................................................. 37
dce_stub_data ................................................. 38
byte_test and byte_jump ........................................... 38
5.5 File Processing .................................................... 38
5.5.1 Overview ................................................... 38
5.5.2 Quick Guide ................................................. 39
5.5.3 Pre-packaged File Magic Rules ....................................... 39
5.5.4 File Policy .................................................. 40
5.5.5 File Capture .................................................. 40
5.5.6 File Events .................................................. 41
5.6 High Availability ................................................... 41
5.6.1 HA ...................................................... 41
5.6.2 Connector ................................................... 42
Connector (parent plugin class) ....................................... 42
TcpConnector ................................................. 42
FileConnector ................................................. 42
5.6.3 Side Channel ................................................. 43
5.7 HTTP Inspector .................................................... 44
5.7.1 Overview ................................................... 44
5.7.2 Configuration ................................................. 45
request_depth and response_depth ...................................... 45
gzip ...................................................... 45
normalize_utf ................................................. 46
decompress_pdf ............................................... 46
decompress_swf ............................................... 46
normalize_javascript ............................................. 46
URI processing ................................................ 46
5.7.3 Detection rules ................................................ 47
http_uri and http_raw_uri .......................................... 48
http_header and http_raw_header ...................................... 49
http_trailer and http_raw_trailer ....................................... 49
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http_cookie and http_raw_cookie ...................................... 50
http_true_ip .................................................. 50
http_client_body ............................................... 50
http_raw_body ................................................ 50
http_method ................................................. 50
http_stat_code ................................................ 50
http_stat_msg ................................................. 50
http_version .................................................. 50
http_raw_request and http_raw_status .................................... 50
file_data and packet data ........................................... 51
5.7.4 Timing issues and combining rule options .................................. 51
5.8 Performance Monitor ................................................. 52
5.8.1 Overview ................................................... 53
5.8.2 Base Tracker ................................................. 53
5.8.3 Flow Tracker ................................................. 53
5.8.4 FlowIP Tracker ................................................ 54
5.8.5 CPU Tracker ................................................. 54
5.8.6 Formatters .................................................. 54
5.9 POP and IMAP .................................................... 54
5.9.1 Overview ................................................... 54
5.9.2 Configuration ................................................. 54
b64_decode_depth .............................................. 54
qp_decode_depth ............................................... 54
bitenc_decode_depth ............................................. 55
uu_decode_depth ............................................... 55
Examples ................................................... 55
5.10 Port Scan ....................................................... 55
5.10.1 Overview ................................................... 56
5.10.2 Scan levels .................................................. 57
5.10.3 Tuning Portscan ............................................... 58
5.11 Sensitive Data Filtering ................................................ 59
5.11.1 Hyperscan .................................................. 59
5.11.2 Syntax .................................................... 59
Pattern .................................................... 59
Threshold ................................................... 60
Obfuscating Credit Cards and Social Security Numbers ........................... 60
5.11.3 Example ................................................... 60
5.11.4 Caveats .................................................... 60
5.12 SMTP ......................................................... 61
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5.12.1 Overview ................................................... 61
5.12.2 Configuration ................................................. 61
normalize and normalize_cmds ....................................... 61
ignore_data .................................................. 61
ignore_tls_data ................................................ 61
max_command_line_len ........................................... 61
max_header_line_len ............................................. 61
max_response_line_len ............................................ 61
alt_max_command_line_len ......................................... 62
invalid_cmds ................................................. 62
valid_cmds .................................................. 62
data_cmds .................................................. 62
binary_data_cmds .............................................. 62
auth_cmds .................................................. 62
xlink2state .................................................. 62
b64_decode_depth .............................................. 62
qp_decode_depth ............................................... 63
bitenc_decode_depth * default to 25 ..................................... 63
uu_decode_depth ............................................... 63
Log Options ................................................. 63
5.12.3 Example ................................................... 63
5.13 Wizard ......................................................... 64
6 Basic Modules 65
6.1 active ......................................................... 65
6.2 alerts .......................................................... 65
6.3 attribute_table ..................................................... 66
6.4 classifications ..................................................... 66
6.5 daq ........................................................... 66
6.6 decode ......................................................... 67
6.7 detection ........................................................ 68
6.8 event_filter ...................................................... 69
6.9 event_queue ...................................................... 69
6.10 high_availability ................................................... 69
6.11 host_cache ....................................................... 70
6.12 host_tracker ...................................................... 70
6.13 hosts .......................................................... 71
6.14 inspection ....................................................... 71
6.15 ips ........................................................... 71
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6.16 latency ......................................................... 72
6.17 memory ........................................................ 72
6.18 network ........................................................ 73
6.19 output ......................................................... 73
6.20 packets ........................................................ 74
6.21 process ........................................................ 74
6.22 profiler ......................................................... 74
6.23 rate_filter ....................................................... 75
6.24 references ....................................................... 75
6.25 rule_state ....................................................... 76
6.26 search_engine ..................................................... 76
6.27 side_channel ..................................................... 77
6.28 snort .......................................................... 77
6.29 suppress ........................................................ 81
7 Codec Modules 81
7.1 arp ........................................................... 82
7.2 auth .......................................................... 82
7.3 ciscometadata ..................................................... 82
7.4 eapol .......................................................... 82
7.5 erspan2 ........................................................ 83
7.6 erspan3 ........................................................ 83
7.7 esp ........................................................... 83
7.8 eth ........................................................... 83
7.9 fabricpath ....................................................... 83
7.10 gre ........................................................... 84
7.11 gtp ........................................................... 84
7.12 icmp4 ......................................................... 84
7.13 icmp6 ......................................................... 85
7.14 igmp .......................................................... 86
7.15 ipv4 .......................................................... 86
7.16 ipv6 .......................................................... 87
7.17 llc ........................................................... 87
7.18 mpls .......................................................... 88
7.19 pbb .......................................................... 88
7.20 pgm .......................................................... 88
7.21 pppoe ......................................................... 89
7.22 tcp ........................................................... 89
7.23 token_ring ....................................................... 90
7.24 udp .......................................................... 90
7.25 vlan .......................................................... 90
7.26 wlan .......................................................... 91
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8 Connector Modules 91
8.1 file_connector ..................................................... 91
8.2 tcp_connector ..................................................... 91
9 Inspector Modules 92
9.1 appid ......................................................... 92
9.2 arp_spoof ....................................................... 92
9.3 back_orifice ...................................................... 93
9.4 binder ......................................................... 93
9.5 data_log ........................................................ 94
9.6 dce_http_proxy .................................................... 94
9.7 dce_http_server .................................................... 95
9.8 dce_smb ........................................................ 95
9.9 dce_tcp ........................................................ 98
9.10 dce_udp ........................................................100
9.11 dnp3 ..........................................................101
9.12 dns ...........................................................101
9.13 dpx ..........................................................102
9.14 file_id .........................................................102
9.15 file_log ........................................................103
9.16 ftp_client .......................................................104
9.17 ftp_data ........................................................104
9.18 ftp_server .......................................................104
9.19 gtp_inspect ......................................................105
9.20 http_inspect ......................................................106
9.21 imap ..........................................................111
9.22 modbus ........................................................112
9.23 normalizer .......................................................112
9.24 packet_capture ....................................................115
9.25 perf_monitor .....................................................115
9.26 pop ..........................................................116
9.27 port_scan .......................................................117
9.28 reg_test ........................................................120
9.29 reputation .......................................................120
9.30 rpc_decode ......................................................121
9.31 sip ...........................................................121
9.32 smtp ..........................................................123
9.33 ssh ...........................................................125
9.34 ssl ...........................................................126
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9.35 stream .........................................................127
9.36 stream_file .......................................................129
9.37 stream_icmp ......................................................129
9.38 stream_ip .......................................................129
9.39 stream_tcp .......................................................131
9.40 stream_udp ......................................................133
9.41 stream_user ......................................................134
9.42 telnet .........................................................134
9.43 wizard .........................................................134
10 IPS Action Modules 135
10.1 react ..........................................................135
10.2 reject .........................................................135
10.3 rewrite .........................................................136
11 IPS Option Modules 136
11.1 ack ...........................................................136
11.2 appids .........................................................136
11.3 asn1 ..........................................................136
11.4 base64_decode ....................................................137
11.5 bufferlen ........................................................137
11.6 byte_extract ......................................................137
11.7 byte_jump .......................................................138
11.8 byte_math .......................................................138
11.9 byte_test ........................................................139
11.10classtype ........................................................139
11.11content .........................................................139
11.12cvs ...........................................................140
11.13dce_iface .......................................................140
11.14dce_opnum ......................................................140
11.15dce_stub_data .....................................................140
11.16detection_filter ....................................................141
11.17dnp3_data .......................................................141
11.18dnp3_func .......................................................141
11.19dnp3_ind .......................................................141
11.20dnp3_obj .......................................................141
11.21dsize ..........................................................142
11.22file_data ........................................................142
11.23file_type ........................................................142
Snort 3 User Manual xi
11.24flags ..........................................................142
11.25flow ..........................................................142
11.26flowbits ........................................................143
11.27fragbits ........................................................143
11.28fragoffset .......................................................143
11.29gid ...........................................................143
11.30gtp_info ........................................................144
11.31gtp_type ........................................................144
11.32gtp_version ......................................................144
11.33http_client_body ...................................................144
11.34http_cookie ......................................................144
11.35http_header ......................................................145
11.36http_method ......................................................145
11.37http_raw_body ....................................................145
11.38http_raw_cookie ...................................................145
11.39http_raw_header ...................................................146
11.40http_raw_request ...................................................146
11.41http_raw_status ....................................................146
11.42http_raw_trailer ....................................................146
11.43http_raw_uri ......................................................147
11.44http_stat_code .....................................................147
11.45http_stat_msg .....................................................147
11.46http_trailer .......................................................148
11.47http_true_ip ......................................................148
11.48http_uri ........................................................148
11.49http_version ......................................................149
11.50icmp_id ........................................................149
11.51icmp_seq .......................................................149
11.52icode ..........................................................149
11.53id ...........................................................149
11.54ip_proto ........................................................150
11.55ipopts .........................................................150
11.56isdataat ........................................................150
11.57itype ..........................................................150
11.58md5 ..........................................................150
11.59metadata ........................................................151
11.60modbus_data .....................................................151
11.61modbus_func .....................................................151
11.62modbus_unit .....................................................151
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11.63msg ..........................................................151
11.64mss ..........................................................152
11.65pcre ..........................................................152
11.66pkt_data ........................................................152
11.67pkt_num ........................................................152
11.68priority ........................................................152
11.69raw_data ........................................................152
11.70reference .......................................................153
11.71regex ..........................................................153
11.72rem ..........................................................153
11.73replace .........................................................153
11.74rev ...........................................................154
11.75rpc ...........................................................154
11.76sd_pattern .......................................................154
11.77seq ...........................................................154
11.78service .........................................................155
11.79session .........................................................155
11.80sha256 .........................................................155
11.81sha512 .........................................................155
11.82sid ...........................................................156
11.83sip_body ........................................................156
11.84sip_header .......................................................156
11.85sip_method ......................................................156
11.86sip_stat_code .....................................................156
11.87so ...........................................................156
11.88soid ..........................................................157
11.89ssl_state ........................................................157
11.90ssl_version ......................................................157
11.91stream_reassemble ..................................................158
11.92stream_size ......................................................158
11.93tag ...........................................................158
11.94target .........................................................158
11.95tos ...........................................................159
11.96ttl ...........................................................159
11.97urg ...........................................................159
11.98window ........................................................159
11.99wscale .........................................................159
12 Search Engine Modules 160
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13 SO Rule Modules 160
14 Logger Modules 160
14.1 alert_csv ........................................................160
14.2 alert_ex ........................................................160
14.3 alert_fast .......................................................161
14.4 alert_full ........................................................161
14.5 alert_json .......................................................161
14.6 alert_sfsocket .....................................................161
14.7 alert_syslog ......................................................162
14.8 alert_unixsock .....................................................162
14.9 log_codecs ......................................................162
14.10log_hext ........................................................162
14.11log_pcap ........................................................163
14.12unified2 ........................................................163
15 DAQ Configuration and Modules 163
15.1 Building the DAQ Library and Its Bundled DAQ Modules ..............................163
15.2 Configuration .....................................................163
15.2.1 Command Line Example ...........................................164
15.2.2 Configuration File Example .........................................164
15.2.3 Interaction With Multiple Packet Threads ..................................164
15.3 DAQ Modules Included With Snort 3 .........................................166
15.3.1 Socket Module ................................................166
15.3.2 File Module ..................................................166
15.3.3 Hext Module .................................................167
16 Snort 3 vs Snort 2 168
16.1 Features New to Snort 3 ................................................168
16.2 Features Improved over Snort 2 ............................................169
16.3 Build Options .....................................................170
16.4 Command Line ....................................................170
16.5 Conf File .......................................................171
16.6 Rules .........................................................172
16.7 Output .........................................................173
16.8 Sensitive Data .....................................................173
Snort 3 User Manual xiv
17 Snort2Lua 173
17.1 Snort2Lua Command Line ..............................................174
17.1.1 Usage: snort2lua [OPTIONS]. . . -c <snort_conf> . . . ............................174
Options: ....................................................174
Required option: ...............................................175
Default values: ................................................175
17.2 Known Problems ...................................................175
17.3 Usage .........................................................176
18 Extending Snort 177
18.1 Plugins ........................................................177
18.2 Modules ........................................................177
18.3 Inspectors .......................................................177
18.4 Codecs .........................................................178
18.5 IPS Actions ......................................................180
18.6 Developers Guide ...................................................180
18.7 Piglet Test Harness ..................................................180
18.8 Piglet Lua API ....................................................181
18.8.1 Plugin Instances ...............................................181
Interface Objects ...............................................183
19 Coding Style 187
19.1 General ........................................................187
19.2 C++ Specific .....................................................187
19.3 Naming ........................................................188
19.4 Comments .......................................................188
19.5 Logging ........................................................189
19.6 Types .........................................................189
19.7 Macros (aka defines) .................................................190
19.8 Formatting .......................................................190
19.9 Headers ........................................................191
19.10Warnings .......................................................192
19.11Uncrustify .......................................................192
20 Reference 192
20.1 Build Options .....................................................192
20.2 Environment Variables ................................................193
20.3 Command Line Options ................................................193
20.4 Configuration .....................................................197
20.5 Counts .........................................................225
Snort 3 User Manual xv
20.6 Generators .......................................................241
20.7 Builtin Rules .....................................................243
20.8 Command Set .....................................................256
20.9 Signals .........................................................257
20.10Configuration Changes ................................................257
20.11Module Listing ....................................................262
20.12Plugin Listing .....................................................268
20.13Bugs ..........................................................275
20.13.1 Build .....................................................275
20.13.2 Config .....................................................275
20.13.3 Rules .....................................................275
20.13.4 snort2lua ...................................................276
20.13.5 Runtime ....................................................276
20.14LibDAQ and DAQ Modules .............................................276
20.14.1 Building the DAQ Library and DAQ Modules ................................276
20.14.2 PCAP Module ................................................277
20.14.3 AFPACKET Module .............................................277
Fanout (Kernel Loadbalancing) .......................................278
20.14.4 NFQ Module .................................................278
20.14.5 IPQ Module ..................................................279
20.14.6 IPFW Module ................................................279
20.14.7 Dump Module ................................................280
20.14.8 Netmap Module ...............................................280
FreeBSD ...................................................280
Linux .....................................................281
20.14.9 Notes on iptables ...............................................281
20.14.10Notes on FreeBSD::IPFW ..........................................282
20.14.11Notes on OpenBSD::IPFW ..........................................283
Snort 3 User Manual 1 / 284
,,_ -*> Snort++ <*-
o" )~ Version 3.0.0 (Build 242) from 2.9.11
’’’’ By Martin Roesch & The Snort Team
http://snort.org/contact#team
Copyright (C) 2014-2017 Cisco and/or its affiliates. All rights reserved.
Copyright (C) 1998-2013 Sourcefire, Inc., et al.
1 Overview
Snort 3.0 is an updated version of the Snort Intrusion Prevention System (IPS) which features a new design that provides a
superset of Snort 2.X functionality with better throughput, detection, scalability, and usability. Some of the key features of Snort
3.0 are:
• Support multiple packet processing threads
• Use a shared configuration and attribute table
• Autodetect services for portless configuration
• Modular design
• Plugin framework with over 200 plugins
• More scalable memory profile
• LuaJIT configuration, loggers, and rule options
• Hyperscan support
• Rewritten TCP handling
• New rule parser and syntax
• Service rules like alert http
• Rule "sticky" buffers
Snort 3 User Manual 2 / 284
• Way better SO rules
• New HTTP inspector
• New performance monitor
• New time and space profiling
• New latency monitoring and enforcement
• Piglets to facilitate component testing
• Inspection Events
• Automake and Cmake
• Autogenerate reference documentation
Additional features are on the road map:
• Use a shared network map
• Support hardware offload for fast pattern acceleration
• Provide support for DPDK and ODP
• Support pipelining of packet processing
• Support proxy mode
• Multi-tennant support
• Incremental reload
• New serialization of perf data and events
• Enhanced rule processing
• Windows support
• Anomaly detection
• and more!
The remainder of this section provides a high level survey of the inputs, processing, and outputs available with Snort 3.0.
Snort++ is the project that is creating Snort 3.0. In this manual "Snort" or "Snort 3" refers to the 3.0 version and earlier versions
will be referred to as "Snort 2" where the distinction is relevant.
1.1 First Steps
Snort can be configured to perform complex packet processing and deep packet inspection but it is best start simply and work up
to more interesting tasks. Snort won’t do anything you didn’t specifically ask it to do so it is safe to just try things out and see
what happens. Let’s start by just running Snort with no arguments:
$ snort
That will output usage information including some basic help commands. You should run all of these commands now to see what
is available:
$ snort -V
$ snort -?
$ snort --help
Snort 3 User Manual 3 / 284
Note that Snort has extensive command line help available so if anything below isn’t clear, there is probably a way to get the
exact information you need from the command line.
Now let’s examine the packets in a capture file (pcap):
$ snort -r a.pcap
Snort will decode and count the packets in the file and output some statistics. Note that the output excludes non-zero numbers so
it is easy to see what is there.
You may have noticed that there are command line options to limit the number of packets examined or set a filter to select
particular packets. Now is a good time to experiment with those options.
If you want to see details on each packet, you can dump the packets to console like this:
$ snort -r a.pcap -L dump
Add the -d option to see the TCP and UDP payload. Now let’s switch to live traffic. Replace eth0 in the below command with an
available network interface:
$ snort -i eth0 -L dump
Unless the interface is taken down, Snort will just keep running, so enter Control-C to terminate or use the -n option to limit the
number of packets.
Generally it is better to capture the packets for later analysis like this:
$ snort -i eth0 -L pcap -n 10
Snort will write 10 packets to log.pcap.# where # is a timestamp value. You can read these back with -r and dump to console or
pcap with -L. You get the idea.
Note that you can do similar things with other tools like tcpdump or Wireshark however these commands are very useful when
you want to check your Snort setup.
The examples above use the default pcap DAQ. Snort supports non-pcap interfaces as well via the DAQ (data acquisition) library.
Other DAQs provide additional functionality such as inline operation and/or higher performance. There are even DAQs that
support raw file processing (ie without packets), socket processing, and plain text packets. To load external DAQ libraries and
see available DAQs or select a particular DAQ use one of these commands:
$ snort --daq-dir <path> --daq-list
$ snort --daq-dir <path> --daq <type>
Be sure to put the --daq-dir option ahead of the --daq-list option or the external DAQs won’t appear in the list.
To leverage intrusion detection features of Snort you will need to provide some configuration details. The next section breaks
down what must be done.
1.2 Configuration
Effective configuration of Snort is done via the environment, command line, a Lua configuration file, and a set of rules.
Note that backwards compatibility with Snort 2 was sacrificed to obtain new and improved functionality. While Snort 3 leverages
some of the Snort 2 code base, a lot has changed. The configuration of Snort 3 is done with Lua, so your old conf won’t work as
is. Rules are still text based but with syntax tweaks, so your 2.X rules must be fixed up. However, snort2lua will help you convert
your conf and rules to the new format.
Snort 3 User Manual 4 / 284
1.2.1 Environment
LUA_PATH must be set based on your install:
LUA_PATH=$install_prefix/include/snort/lua/\?.lua\;\;
SNORT_LUA_PATH must be set to load auxiliary configuration files if you use the default snort.lua. For example:
export SNORT_LUA_PATH=$install_prefix/etc/snort
1.2.2 Command Line
A simple command line might look like this:
snort -c snort.lua -R cool.rules -r some.pcap -A cmg
To understand what that does, you can start by just running snort with no arguments by running snort --help. Help for all
configuration and rule options is available via a suitable command line. In this case:
-c snort.lua is the main configuration file. This is a Lua script that is executed when loaded.
-R cool.rules contains some detection rules. You can write your own or obtain them from Talos (native 3.0 rules are not yet
available from Talos so you must convert them with snort2lua). You can also put your rules directly in your configuration file.
-r some.pcap tells Snort to read network traffic from the given packet capture file. You could instead use -i eth0 to read from a
live interface. There many other options available too depending on the DAQ you use.
-A cmg says to output intrusion events in "cmg" format, which has basic header details followed by the payload in hex and text.
Note that you add to and/or override anything in your configuration file by using the --lua command line option. For example:
--lua ’ips = { enable_builtin_rules = true }’
will load the built-in decoder and inspector rules. In this case, ips is overwritten with the config you see above. If you just want
to change the config given in your configuration file you would do it like this:
--lua ’ips.enable_builtin_rules = true’
1.2.3 Configuration File
The configuration file gives you complete control over how Snort processes packets. Start with the default snort.lua included in
the distribution because that contains some key ingredients. Note that most of the configurations look like:
stream = { }
This means enable the stream module using internal defaults. To see what those are, you could run:
snort --help-config stream
Snort is organized into a collection of builtin and plugin modules. If a module has parameters, it is configured by a Lua table of
the same name. For example, we can see what the active module has to offer with this command:
$ snort --help-module active
What: configure responses
Type: basic
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Configuration:
int active.attempts = 0: number of TCP packets sent per response (with
varying sequence numbers) { 0:20 }
string active.device: use ’ip’ for network layer responses or ’eth0’ etc
for link layer
string active.dst_mac: use format ’01:23:45:67:89:ab’
int active.max_responses = 0: maximum number of responses { 0: }
int active.min_interval = 255: minimum number of seconds between
responses { 1: }
This says active is a basic module that has several parameters. For each, you will see:
type module.name = default: help { range }
For example, the active module has a max_responses parameter that takes non-negative integer values and defaults to zero. We
can change that in Lua as follows:
active = { max_responses = 1 }
or:
active = { }
active.max_responses = 1
If we also wanted to limit retries to at least 5 seconds, we could do:
active = { max_responses = 1, min_interval = 5 }
1.2.4 Rules
Rules determine what Snort is looking for. They can be put directly in your Lua configuration file with the ips module, on the
command line with --lua, or in external files. Generally you will have many rules obtained from various sources such as Talos
and loading external files is the way to go so we will summarize that here. Add this to your Lua configuration:
ips = { include = ’rules.txt’ }
to load the external rules file named rules.txt. You can only specify one file this way but rules files can include other rules files
with the include statement. In addition you can load rules like:
$ sort -c snort.lua -R rules.txt
You can use both approaches together.
1.2.5 Converting Your 2.X Configuration
If you have a working 2.X configuration snort2lua makes it easy to get up and running with Snort 3. This tool will convert your
configuration and/or rules files automatically. You will want to clean up the results and double check that it is doing exactly what
you need.
snort2lua -c snort.conf
The above command will generate snort.lua based on your 2.X configuration. For more information and options for more
sophisticated use cases, see the Snort2Lua section later in the manual.
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1.3 Output
Snort can produce quite a lot of data. In the following we will summarize the key aspects of the core output types. Additional
data such as from appid is covered later.
1.3.1 Basic Statistics
At shutdown, Snort will output various counts depending on configuration and the traffic processed. Generally, you may see:
• Packet Statistics - this includes data from the DAQ and decoders such as the number of packets received and number of UDP
packets.
• Module Statistics - each module tracks activity via a set of peg counts that indicate how many times something was observed
or performed. This might include the number of HTTP GET requests processed and the number of TCP reset packets trimmed.
• File Statistics - look here for a breakdown of file type, bytes, signatures.
• Summary Statistics - this includes total runtime for packet processing and the packets per second. Profiling data will appear
here as well if configured.
Note that only the non-zero counts are output. Run this to see the available counts:
$ snort --help-counts
1.3.2 Alerts
If you configured rules, you will need to configure alerts to see the details of detection events. Use the -A option like this:
$ snort -c snort.lua -r a.pcap -A cmg
There are many types of alert outputs possible. Here is a brief list:
• -A cmg is the same as -A fast -d -e and will show information about the alert along with packet headers and payload.
• -A u2 is the same as -A unified2 and will log events and triggering packets in a binary file that you can feed to other tools
for post processing. Note that Snort 3 does not provide the raw packets for alerts on PDUs; you will get the actual buffer that
alerted.
• -A csv will output various fields in comma separated value format. This is entirely customizable and very useful for pcap
analysis.
To see the available alert types, you can run this command:
$ snort --list-plugins | grep logger
1.3.3 Files and Paths
Note that output is specific to each packet thread. If you run 4 packet threads with u2 output, you will get 4 different u2 files.
The basic structure is:
<logdir>/[<run_prefix>][<id#>][<X>]<name>
where:
• logdir is set with -l and defaults to ./
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• run_prefix is set with --run-prefix else not used
• id# is the packet thread number that writes the file; with one packet thread, id# (zero) is omitted without --id-zero
• X is / if you use --id-subdir, else _ if id# is used
• name is based on module name that writes the file
Additional considerations:
• There is no way to explicitly configure a full path to avoid issues with multiple packet threads.
• All text mode outputs default to stdout
1.3.4 Performance Statistics
Still more data is available beyond the above.
• By configuring the perf_monitor module you can capture a configurable set of peg counts during runtime. This is useful to
feed to an external program so you can see what is happening without stopping Snort.
• The profiler module allows you to track time and space used by module and rules. Use this data to tune your system for best
performance. The output will show up under Summary Statistics at shutdown.
2 Concepts
This section provides background on essential aspects of Snort’s operation.
2.1 Terminology
•basic module: a module integrated into Snort that does not come from a plugin.
•binder: inspector that maps configuration to traffic
•builtin rules: codec and inspector rules for anomalies detected internally.
•codec: short for coder / decoder. These plugins are used for basic protocol decoding, anomaly detection, and construction of
active responses.
•data module: an adjunct configuration plugin for use with certain inspectors.
•dynamic rules: plugin rules loaded at runtime. See SO rules.
•fast pattern: the content in an IPS rule that must be found by the search engine in order for a rule to be evaluated.
•fast pattern matcher: see search engine.
•hex: a type of protocol magic that the wizard uses to identify binary protocols.
•inspector: plugin that processes packets (similar to the Snort 2 preprocessor)
•IPS: intrusion prevention system, like Snort.
•IPS action: plugin that allows you to perform custom actions when events are generated. Unlike loggers, these are invoked
before thresholding and can be used to control external agents or send active responses.
•IPS option: this plugin is the building blocks of IPS rules.
•logger: a plugin that performs output of events and packets. Events are thresholded before reaching loggers.
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•module: the user facing portion of a Snort component. Modules chiefly provide configuration parameters, but may also provide
commands, builtin rules, profiling statistics, peg counts, etc. Note that not all modules are plugins and not all plugins have
modules.
•peg count: the number of times a given event or condition occurs.
•plugin: one of several types of software components that can be loaded from a dynamic library when Snort starts up. Some
plugins are coupled with the main engine in such a way that they must be built statically, but a newer version can be loaded
dynamically.
•search engine: a plugin that performs multipattern searching of packets and payload to find rules that should be evaluated.
There are currently no specific modules, although there are several search engine plugins. Related configuration is done with
the basic detection module. Aka fast pattern matcher.
•SO rule: a IPS rule plugin that performs custom detection that can’t be done by a text rule. These rules typically do not have
associated modules. SO comes from shared object, meaning dynamic library.
•spell: a type of protocol magic that the wizard uses to identify ASCII protocols.
•text rule: a rule loaded from the configuration that has a header and body. The header specifies action, protocol, source and
destination IP addresses and ports, and direction. The body specifies detection and non-detection options.
•wizard: inspector that applies protocol magic to determine which inspectors should be bound to traffic absent a port specific
binding. See hex and spell.
2.2 Modules
Modules are the building blocks of Snort. They encapsulate the types of data that many components need including parameters,
peg counts, profiling, builtin rules, and commands. This allows Snort to handle them generically and consistently. You can learn
quite a lot about any given module from the command line. For example, to see what stream_tcp is all about, do this:
$ snort --help-config stream_tcp
Modules are configured using Lua tables with the same name. So the stream_tcp module is configured with defaults like this:
stream_tcp = { }
The earlier help output showed that the default session tracking timeout is 30 seconds. To change that to 60 seconds, you can
configure it this way:
stream_tcp = { session_timeout = 60 }
Or this way:
stream_tcp = { }
stream_tcp.session_timeout = 60
More on parameters is given in the next section.
Other things to note about modules:
• Shutdown output will show the non-zero peg counts for all modules. For example, if stream_tcp did anything, you would see
the number of sessions processed among other things.
• Providing the builtin rules allows the documentation to include them automatically and also allows for autogenerating the rules
at startup.
• Only a few module provide commands at this point, most notably the snort module.
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2.3 Parameters
Parameters are given with this format:
type name = default: help { range }
The following types are used:
•addr: any valid IP4 or IP6 address or CIDR
•addr_list: a space separated list of addr values
•bit_list: a list of consecutive integer values from 1 to the range maximum
•bool: true or false
•dynamic: a select type determined by loaded plugins
•enum: a string selected from the given range
•implied: an IPS rule option that takes no value but means true
•int: a whole number in the given range
•interval: a set of ints (see below)
•ip4: an IP4 address or CIDR
•mac: an ethernet address with the form 01:02:03:04:05:06
•multi: one or more space separated strings from the given range
•port: an int in the range 0:65535 indicating a TCP or UDP port number
•real: a real number in the given range
•select: a string selected from the given range
•string: any string with no more than the given length, if any
The parameter name may be adorned in various ways to indicate additional information about the type and use of the parameter:
• For Lua configuration (not IPS rules), if the name ends with [] it is a list item and can be repeated.
• For IPS rules only, names starting with ~ indicate positional parameters. The names of such parameters do not appear in the
rule.
• IPS rules may also have a wild card parameter, which is indicated by a *. Used for unquoted, comma-separated lists such as
service and metadata.
• The snort module has command line options starting with a -.
Some additional details to note:
• Table and variable names are case sensitive; use lower case only.
• String values are case sensitive too; use lower case only.
• Numeric ranges may be of the form low:high where low and high are bounds included in the range. If either is omitted, there
is no hard bound. E.g. 0: means any x where x >= 0.
• Strings may have a numeric range indicating a length limit; otherwise there is no hard limit.
• bit_list is typically used to store a set of byte, port, or VLAN ID values.
• interval takes the form [operator]i, j<>k, or j<⇒k where i,j,k are integers and operator is one of =, !, != (same as !), <, ⇐, >,
>=. j<>k means j < int < k and j<⇒k means j ⇐int ⇐k.
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2.4 Plugins
Snort uses a variety of plugins to accomplish much of its processing objectives, including:
• Codec - to decode and encode packets
• Inspector - like Snort 2 preprocessors, for normalization, etc.
• IpsOption - for detection in Snort rules
• IpsAction - for custom actions
• Logger - for handling events
• Mpse - for fast pattern matching
• So - for dynamic rules
The power of plugins is that they have a very focused purpose and can be created with relative ease. For example, you can extend
the rule language by writing your own IpsOption and it will plug in and function just like existing options. The extra directory
has examples of each type of plugin.
Most plugins can be built statically or dynamically. By default they are all static. There is no difference in functionality between
static or dynamic plugins but the dynamic build generates a slightly lighter weight binary. Either way you can add dynamic
plugins with --plugin-path and newer versions will replace older versions, even when built statically.
A single dynamic library may contain more than one plugin. For example, an inspector will typically be packaged together with
any associated rule options.
2.5 Operation
Snort is a signature-based IPS, which means that as it receives network packets it reassembles and normalizes the content so that
a set of rules can be evaluated to detect the presence of any significant conditions that merit further action. A rough processing
flow is as follows:
The steps are:
1. Decode each packet to determine the basic network characteristics such as source and destination addresses and ports.
A typical packet might have ethernet containing IP containing TCP containing HTTP (ie eth:ip:tcp:http). The various
encapsulating protocols are examined for sanity and anomalies as the packet is decoded. This is essentially a stateless
effort.
2. Preprocess each decoded packet using accumulated state to determine the purpose and content of the innermost message.
This step may involve reordering and reassembling IP fragments and TCP segments to produce the original application
protocol data unit (PDU). Such PDUs are analyzed and normalized as needed to support further processing.
3. Detection is a two step process. For efficiency, most rules contain a specific content pattern that can be searched for such
that if no match is found no further processing is necessary. Upon start up, the rules are compiled into pattern groups such
that a single, parallel search can be done for all patterns in the group. If any match is found, the full rule is examined
according to the specifics of the signature.
4. The logging step is where Snort saves any pertinent information resulting from the earlier steps. More generally, this is
where other actions can be taken as well such as blocking the packet.
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2.5.1 Snort 2 Processing
The preprocess step in Snort 2 is highly configurable. Arbitrary preprocessors can be loaded dynamically at startup, configured
in snort.conf, and then executed at runtime. Basically, the preprocessors are put into a list which is iterated for each packet.
Recent versions have tweaked the list handling some, but the same basic architecture has allowed Snort 2 to grow from a sniffer,
with no preprocessing, to a full-fledged IPS, with lots of preprocessing.
While this "list of plugins" approach has considerable flexibility, it hampers future development when the flow of data from one
preprocessor to the next depends on traffic conditions, a common situation with advanced features like application identification.
In this case, a preprocessor like HTTP may be extracting and normalizing data that ultimately is not used, or appID may be
repeatedly checking for data that is just not available.
Callbacks help break out of the preprocess straitjacket. This is where one preprocessor supplies another with a function to call
when certain data is available. Snort has started to take this approach to pass some HTTP and SIP preprocessor data to appID.
However, it remains a peripheral feature and still requires the production of data that may not be consumed.
2.5.2 Snort 3 Processing
One of the goals of Snort 3 is to provide a more flexible framework for packet processing by implementing an event-driven
approach. Another is to produce data only when needed to minimize expensive normalizations. However, the basic packet
processing provides very similar functionality.
The basic processing steps Snort 3 takes are similar to Snort 2 as seen in the following diagram. The preprocess step employs
specific inspector types instead of a generalized list, but the basic procedure includes stateless packet decoding, TCP stream
reassembly, and service specific analysis in both cases. (Snort 3 provides hooks for arbitrary inspectors, but they are not central
to basic flow processing and are not shown.)
However, Snort 3 also provides a more flexible mechanism than callback functions. By using inspection events, it is possible for
an inspector to supply data that other inspectors can process. This is known as the observer pattern or publish-subscribe pattern.
Note that the data is not actually published. Instead, access to the data is published, and that means that subscribers can access
the raw or normalized version(s) as needed. Normalizations are done only on the first access, and subsequent accesses get the
previously normalized data. This results in just in time (JIT) processing.
A basic example of this in action is provided by the extra data_log plugin. It is a passive inspector, ie it does nothing until it
receives the data it subscribed for (other in the above diagram). By adding the following to your snort.lua configuration, you will
get a simple URI logger.
data_log = { key = ’http_raw_uri’ }
Inspection events coupled with pluggable inspectors provide a very flexible framework for implementing new features. And JIT
buffer stuffers allow Snort to work smarter, not harder. These capabilities will be leveraged more and more as Snort development
continues.
2.6 Rules
Rules tell Snort how to detect interesting conditions, such as an attack, and what to do when the condition is detected. Here is an
example rule:
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alert tcp any any -> 192.168.1.1 80 ( msg:"A ha!"; content:"attack"; sid:1; )
The structure is:
action proto source dir dest ( body )
Where:
action - tells Snort what to do when a rule "fires", ie when the signature matches. In this case Snort will log the event. It can also
do thing like block the flow when running inline.
proto - tells Snort what protocol applies. This may be ip, icmp, tcp, udp, http, etc.
source - specifies the sending IP address and port, either of which can be the keyword any, which is a wildcard.
dir - must be either unidirectional as above or bidirectional indicated by <>.
dest - similar to source but indicates the receiving end.
body - detection and other information contained in parenthesis.
There are many rule options available to construct as sophisticated a signature as needed. In this case we are simply looking for
the "attack" in any TCP packet. A better rule might look like this:
alert http
(
msg:"Gotcha!";
flow:established, to_server;
http_uri:"attack";
sid:2;
)
Note that these examples have a sid option, which indicates the signature ID. In general rules are specified by gid:sid:rev notation,
where gid is the generator ID and rev is the revision of the rule. By default, text rules are gid 1 and shared-object (SO) rules are
gid 3. The various components within Snort that generate events have 1XX gids, for example the decoder is gid 116. You can
list the internal gids and sids with these commands:
$ snort --list-gids
$ snort --list-builtin
For details on these and other options, see the reference section.
2.7 Pattern Matching
Snort evaluates rules in a two-step process which includes a fast pattern search and full evaluation of the signature. More details
on this process follow.
2.7.1 Rule Groups
When Snort starts or reloads configuration, rules are grouped by protocol, port and service. For example, all TCP rules using
the HTTP_PORTS variable will go in one group and all service HTTP rules will go in another group. These rule groups are
compiled into multipattern search engines (MPSE) which are designed to search for all patterns with just a single pass through
a given packet or buffer. You can select the algorithm to use for fast pattern searches with search_engine.search_method which
defaults to ac_bnfa, which balances speed and memory. For a faster search at the expense of significantly more memory, use
ac_full. For best performance and reasonable memory, download the hyperscan source from Intel.
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2.7.2 Fast Patterns
Fast patterns are content strings that have the fast_pattern option or which have been selected by Snort automatically to be used
as a fast pattern. Snort will by default choose the longest pattern in the rule since that is likely to be most unique. That is not
always the case so add fast_pattern to the appropriate content option for best performance. The ideal fast pattern is one which,
if found, is very likely to result in a rule match. Fast patterns that match frequently for unrelated traffic will cause Snort to work
hard with little to show for it.
Certain contents are not eligible to be used as fast patterns. Specifically, if a content is negated, then if it is also relative to another
content, case sensitive, or has non-zero offset or depth, then it is not eligible to be used as a fast pattern.
2.7.3 Rule Evaluation
For each fast pattern match, the corresponding rule(s) are evaluated left-to-right. Rule evaluation requires checking each detection
option in a rule and is a fairly costly process which is why fast patterns are so important. Rule evaluation aborts on the first non-
matching option.
When rule evaluation takes place, the fast pattern match will automatically be skipped if possible. Note that this differs from
Snort 2 which provided the fast_pattern:only option to designate such cases. This is one less thing for the rule writer to worry
about.
3 Tutorial
The section will walk you through building and running Snort. It is not exhaustive but, once you master this material, you should
be able to figure out more advanced usage.
3.1 Dependencies
Required:
• autotools or cmake to build from source
• daq from http://www.snort.org for packet IO
• g++ >= 4.8 or other recent C++11 compiler
• dnet from https://github.com/dugsong/libdnet.git for network utility functions
• hwloc from https://www.open-mpi.org/projects/hwloc/ for CPU affinity management
• LuaJIT from http://luajit.org for configuration and scripting
• OpenSSL from https://www.openssl.org/source/ for SHA and MD5 file signatures, the protected_content rule option, and SSL
service detection
• pcap from http://www.tcpdump.org for tcpdump style logging
• pcre from http://www.pcre.org for regular expression pattern matching
• pkgconfig from https://www.freedesktop.org/wiki/Software/pkg-config/ to locate build dependencies
• zlib from http://www.zlib.net for decompression (>= 1.2.8 recommended)
Optional:
• asciidoc from http://www.methods.co.nz/asciidoc/ to build the HTML manual
• cpputest from http://cpputest.github.io to run additional unit tests with make check
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• dblatex from http://dblatex.sourceforge.net to build the pdf manual (in addition to asciidoc)
• flatbuffers from https://google.github.io/flatbuffers/ for enabling the flatbuffers serialization format
• hyperscan >= 4.4.0 from https://github.com/01org/hyperscan to build new the regex and sd_pattern rule options and hyperscan
search engine
• iconv from https://ftp.gnu.org/pub/gnu/libiconv/ for converting UTF16-LE filenames to UTF8 (usually included in glibc)
• lzma >= 5.1.2 from http://tukaani.org/xz/ for decompression of SWF and PDF files
• safec from https://sourceforge.net/projects/safeclib/ for runtime bounds checks on certain legacy C-library calls
• source-highlight from http://www.gnu.org/software/src-highlite/ to generate the dev guide
• w3m from http://sourceforge.net/projects/w3m/ to build the plain text manual
• uuid from uuid-dev package for unique identifiers
3.2 Building
• Optionally built features are listed in the reference section.
• Create an install path:
export my_path=/path/to/snorty
mkdir -p $my_path
• If you are using a github clone with autotools, do this:
autoreconf -isvf
• Now do one of the following:
a. To build with autotools, simply do the usual from the top level directory:
./configure --prefix=$my_path
make -j 8
make install
b. To build with cmake and make, run configure_cmake.sh. It will automatically create and populate a new subdirectory
named build.
./configure_cmake.sh --prefix=$my_path
cd build
make -j 8
make install
ln -s $my_path/conf $my_path/etc
c. You can also specify a cmake project generator:
./configure_cmake.sh --generator=Xcode --prefix=$my_path
d. Or use ccmake directly to configure and generate from an arbitrary build directory like one of these:
ccmake -G Xcode /path/to/Snort++/tree
open snort.xcodeproj
ccmake -G "Eclipse CDT4 - Unix Makefiles" /path/to/Snort++/tree
run eclipse and do File > Import > Existing Eclipse Project
• To build with g++ on OS X where clang is installed, do this first:
export CXX=g++
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3.3 Running
First set up the environment:
export LUA_PATH=$my_path/include/snort/lua/\?.lua\;\;
export SNORT_LUA_PATH=$my_path/etc/snort/
Then give it a go:
• Get some help:
$my_path/bin/snort --help
$my_path/bin/snort --help-module suppress
$my_path/bin/snort --help-config | grep thread
• Examine and dump a pcap:
$my_path/bin/snort -r <pcap>
$my_path/bin/snort -L dump -d -e -q -r <pcap>
• Verify config, with or w/o rules:
$my_path/bin/snort -c $my_path/etc/snort/snort.lua
$my_path/bin/snort -c $my_path/etc/snort/snort.lua -R $my_path/etc/snort/sample. ←-
rules
• Run IDS mode. To keep it brief, look at the first n packets in each file:
$my_path/bin/snort -c $my_path/etc/snort/snort.lua -R $my_path/etc/snort/sample. ←-
rules \
-r <pcap> -A alert_test -n 100000
• Let’s suppress 1:2123. We could edit the conf or just do this:
$my_path/bin/snort -c $my_path/etc/snort/snort.lua -R $my_path/etc/snort/sample. ←-
rules \
-r <pcap> -A alert_test -n 100000 --lua "suppress = { { gid = 1, sid = 2123 } ←-
}"
• Go whole hog on a directory with multiple packet threads:
$my_path/bin/snort -c $my_path/etc/snort/snort.lua -R $my_path/etc/snort/sample. ←-
rules \
--pcap-filter \*.pcap --pcap-dir <dir> -A alert_fast -n 1000 --max-packet- ←-
threads 8
For more examples, see the usage section.
3.4 Tips
One of the goals of Snort 3 is to make it easier to configure your sensor. Here is a summary of tips and tricks you may find useful.
General Use
• Snort tries hard not to error out too quickly. It will report multiple semantic errors.
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• Snort always assumes the simplest mode of operation. Eg, you can omit the -T option to validate the conf if you don’t provide
a packet source.
• Warnings are not emitted unless --warn-* is specified. --warn-all enables all warnings, and --pedantic makes such warnings
fatal.
• You can process multiple sources at one time by using the -z or --max-threads option.
• To make it easy to find the important data, zero counts are not output at shutdown.
• Load plugins from the command line with --plugin-path /path/to/install/lib.
• You can process multiple sources at one time by using the -z or --max-threads option.
• Unit tests are configured with --enable-unit-tests. They can then be run with snort --catch-test [tags]|all.
Lua Configuration
• Configure the wizard and default bindings will be created based on configured inspectors. No need to explicitly bind ports in
this case.
• You can override or add to your Lua conf with the --lua command line option.
• The Lua conf is a live script that is executed when loaded. You can add functions, grab environment variables, compute values,
etc.
• You can also rename symbols that you want to disable. For example, changing normalizer to Xnormalizer (an unknown
symbol) will disable the normalizer. This can be easier than commenting in some cases.
• By default, symbols unknown to Snort are silently ignored. You can generate warnings for them with --warn-unknown. To
ignore such symbols, export them in the environment variable SNORT_IGNORE.
Writing and Loading Rules
Snort rules allow arbitrary whitespace. Multi-line rules make it easier to structure your rule for clarity. There are multiple ways
to add comments to your rules:
• The # character starts a comment to end of line. In addition, all lines between #begin and #end are comments.
• The rem option allows you to write a comment that is conveyed with the rule.
• C style multi-line comments are allowed, which means you can comment out portions of a rule while testing it out by putting
the options between /* and */.
There are multiple ways to load rules too:
• Set ips.rules or ips.include.
• include statements can be used in rules files.
• Use -R to load a rules file.
• Use --stdin-rules with command line redirection.
• Use --lua to specify one or more rules as a command line argument.
Output Files
To make it simple to configure outputs when you run with multiple packet threads, output files are not explicitly configured.
Instead, you can use the options below to format the paths:
<logdir>/[<run_prefix>][<id#>][<X>]<name>
Snort 3 User Manual 17 / 284
• logdir is set with -l and defaults to ./
• run_prefix is set with --run-prefix else not used
• id# is the packet thread number that writes the file; with one packet thread, id# (zero) is omitted without --id-zero
• X is / if you use --id-subdir, else _ if id# is used
• name is based on module name that writes the file
• all text mode outputs default to stdout
3.5 Help
Snort has several options to get more help:
-? list command line options (same as --help)
--help this overview of help
--help-commands [<module prefix>] output matching commands
--help-config [<module prefix>] output matching config options
--help-counts [<module prefix>] output matching peg counts
--help-module <module> output description of given module
--help-modules list all available modules with brief help
--help-plugins list all available plugins with brief help
--help-options [<option prefix>] output matching command line options
--help-signals dump available control signals
--list-buffers output available inspection buffers
--list-builtin [<module prefix>] output matching builtin rules
--list-gids [<module prefix>] output matching generators
--list-modules [<module type>] list all known modules
--list-plugins list all known modules
--show-plugins list module and plugin versions
--help*and --list*options preempt other processing so should be last on the
command line since any following options are ignored. To ensure options like
--markup and --plugin-path take effect, place them ahead of the help or list
options.
Options that filter output based on a matching prefix, such as --help-config
won’t output anything if there is no match. If no prefix is given, everything
matches.
Report bugs to bugs@snort.org.
3.6 Common Errors
FATAL: snort_config is required
• add this line near top of file:
require(’snort_config’)
PANIC: unprotected error in call to Lua API (cannot open snort_defaults.lua: No such file or directory)
• export SNORT_LUA_PATH to point to any dofiles
ERROR can’t find xyz
Snort 3 User Manual 18 / 284
• if xyz is the name of a module, make sure you are not assigning a scalar where a table is required (e.g. xyz = 2 should be xyz
= { }).
ERROR can’t find x.y
• module x does not have a parameter named y. check --help-module x for available parameters.
ERROR invalid x.y = z
• the value z is out of range for x.y. check --help-config x.y for the range allowed.
ERROR: x = { y = z } is in conf but is not being applied
• make sure that x = { } isn’t set later because it will override the earlier setting. same for x.y.
FATAL: can’t load lua/errors.lua: lua/errors.lua:68: =expected near ’;’
• this is a syntax error reported by Lua to Snort on line 68 of errors.lua.
ERROR: rules(2) unknown rule keyword: find.
• this was due to not including the --script-path.
WARNING: unknown symbol x
• if you any variables, you can squelch such warnings by setting them in an environment variable SNORT_IGNORE. to ignore
x, y, and z:
export SNORT_IGNORE="x y z"
3.7 Gotchas
• A nil key in a table will not caught. Neither will a nil value in a table. Neither of the following will cause errors, nor will they
actually set http_server.post_depth:
http_server = { post_depth }
http_server = { post_depth = undefined_symbol }
• It is not an error to set a value multiple times. The actual value applied may not be the last in the table either. It is best to avoid
such cases.
http_server =
{
post_depth = 1234,
post_depth = 4321
}
• Snort can’t tell you the exact filename or line number of a semantic error but it will tell you the fully qualified name.
• The dump DAQ will not work with multiple threads unless you use --daq-var file=/dev/null. This will be fixed in at some point
to use the Snort log directory, etc.
• configure will use clang by default if it is installed.To compile with g instead:
export CXX=g++
Snort 3 User Manual 19 / 284
• If you build with hyperscan on OS X and see:
dyld: Library not loaded: @rpath/libhs.4.0.dylib
when you try to run src/snort, export DYLD_LIBRARY_PATH with the path to
libhs. You can also do:
install_name_tool -change @rpath/libhs.4.0.dylib \
/path-to/libhs.4.0.dylib src/snort
4 Usage
For the following examples "$my_path" is assumed to be the path to the Snort install directory. Additionally, it is assumed that
"$my_path/bin" is in your PATH.
4.1 Environment
LUA_PATH is used directly by Lua to load and run required libraries. SNORT_LUA_PATH is used by Snort to load supplemental
configuration files.
export LUA_PATH=$my_path/include/snort/lua/\?.lua\;\;
export SNORT_LUA_PATH=$my_path/etc/snort
4.2 Help
Print the help summary:
snort --help
Get help on a specific module ("stream", for example):
snort --help-module stream
Get help on the "-A" command line option:
snort --help-options A
Grep for help on threads:
snort --help-config | grep thread
Output help on "rule" options in AsciiDoc format:
snort --markup --help-options rule
Note
Snort stops reading command-line options after the "--help-" and "--list-" options, so any other options should be placed before
them.
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4.3 Sniffing and Logging
Read a pcap:
snort -r /path/to/my.pcap
Dump the packets to stdout:
snort -r /path/to/my.pcap -L dump
Dump packets with application data and layer 2 headers
snort -r /path/to/my.pcap -L dump -d -e
Note
Command line options must be specified separately. "snort -de" won’t work. You can still concatenate options and their
arguments, however, so "snort -Ldump" will work.
Dump packets from all pcaps in a directory:
snort --pcap-dir /path/to/pcap/dir --pcap-filter ’*.pcap’ -L dump -d -e
Log packets to a directory:
snort --pcap-dir /path/to/pcap/dir --pcap-filter ’*.pcap’ -L dump -l /path/to/log/ ←-
dir
4.4 Configuration
Validate a configuration file:
snort -c $my_path/etc/snort/snort.lua
Validate a configuration file and a separate rules file:
snort -c $my_path/etc/snort/snort.lua -R $my_path/etc/snort/sample.rules
Read rules from stdin and validate:
snort -c $my_path/etc/snort/snort.lua --stdin-rules < $my_path/etc/snort/sample. ←-
rules
Enable warnings for Lua configurations and make warnings fatal:
snort -c $my_path/etc/snort/snort.lua --warn-all --pedantic
Tell Snort where to look for additional Lua scripts:
snort --script-path /path/to/script/dir
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4.5 IDS mode
Run Snort in IDS mode, reading packets from a pcap:
snort -c $my_path/etc/snort/snort.lua -r /path/to/my.pcap
Log any generated alerts to the console using the "-A" option:
snort -c $my_path/etc/snort/snort.lua -r /path/to/my.pcap -A alert_full
Capture separate stdout, stderr, and stdlog files (out has startup and shutdown output, err has warnings and errors, and log has
alerts):
snort -c $my_path/etc/snort/snort.lua -r /path/to/my.pcap -A csv \
1>out 2>err 3>log
Add or modify a configuration from the command line using the "--lua" option:
snort -c $my_path/etc/snort/snort.lua -r /path/to/my.pcap -A cmg \
--lua ’ips = { enable_builtin_rules = true }’
Note
The "--lua" option can be specified multiple times.
Run Snort in IDS mode on an entire directory of pcaps, processing each input source on a separate thread:
snort -c $my_path/etc/snort/snort.lua --pcap-dir /path/to/pcap/dir \
--pcap-filter ’*.pcap’ --max-packet-threads 8
Run Snort on 2 interfaces, eth0 and eth1:
snort -c $my_path/etc/snort/snort.lua -i "eth0 eth1" -z 2 -A cmg
Run Snort inline with the afpacket DAQ:
snort -c $my_path/etc/snort/snort.lua --daq afpacket -i "eth0:eth1" \
-A cmg
4.6 Plugins
Load external plugins and use the "ex" alert:
snort -c $my_path/etc/snort/snort.lua \
--plugin-path $my_path/lib/snort_extra \
-A alert_ex -r /path/to/my.pcap
Test the LuaJIT rule option find loaded from stdin:
snort -c $my_path/etc/snort/snort.lua \
--script-path $my_path/lib/snort_extra \
--stdin-rules -A cmg -r /path/to/my.pcap << END
alert tcp any any -> any 80 (
sid:3; msg:"found"; content:"GET";
find:"pat=’HTTP/1%.%d’" ; )
END
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4.7 Output Files
To make it simple to configure outputs when you run with multiple packet threads, output files are not explicitly configured.
Instead, you can use the options below to format the paths:
<logdir>/[<run_prefix>][<id#>][<X>]<name>
Log to unified in the current directory:
snort -c $my_path/etc/snort/snort.lua -r /path/to/my.pcap -A unified2
Log to unified in the current directory with a different prefix:
snort -c $my_path/etc/snort/snort.lua -r /path/to/my.pcap -A unified2 \
--run-prefix take2
Log to unified in /tmp:
snort -c $my_path/etc/snort/snort.lua -r /path/to/my.pcap -A unified2 -l /tmp
Run 4 packet threads and log with thread number prefix (0-3):
snort -c $my_path/etc/snort/snort.lua --pcap-dir /path/to/pcap/dir \
--pcap-filter ’*.pcap’ -z 4 -A unified2
Run 4 packet threads and log in thread number subdirs (0-3):
snort -c $my_path/etc/snort/snort.lua --pcap-dir /path/to/pcap/dir \
--pcap-filter ’*.pcap’ -z 4 -A unified2 --id-subdir
Note
subdirectories are created automatically if required. Log filename is based on module name that writes the file. All text mode
outputs default to stdout. These options can be combined.
4.8 DAQ Alternatives
Process hext packets from stdin:
snort -c $my_path/etc/snort/snort.lua \
--daq-dir $my_path/lib/snort/daqs --daq hext -i tty << END
$packet 10.1.2.3 48620 -> 10.9.8.7 80
"GET / HTTP/1.1\r\n"
"Host: localhost\r\n"
"\r\n"
END
Process raw ethernet from hext file:
snort -c $my_path/etc/snort/snort.lua \
--daq-dir $my_path/lib/snort/daqs --daq hext \
--daq-var dlt=1 -r <hext-file>
Process a directory of plain files (ie non-pcap) with 4 threads with 8K buffers:
snort -c $my_path/etc/snort/snort.lua \
--daq-dir $my_path/lib/snort/daqs --daq file \
--pcap-dir path/to/files -z 4 -s 8192
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Bridge two TCP connections on port 8000 and inspect the traffic:
snort -c $my_path/etc/snort/snort.lua \
--daq-dir $my_path/lib/snort/daqs --daq socket
4.9 Logger Alternatives
Dump TCP stream payload in hext mode:
snort -c $my_path/etc/snort/snort.lua -L hext
Output timestamp, pkt_num, proto, pkt_gen, dgm_len, dir, src_ap, dst_ap, rule, action for each alert:
snort -c $my_path/etc/snort/snort.lua -A csv
Output the old test format alerts:
snort -c $my_path/etc/snort/snort.lua \
--lua "alert_csv = { fields = ’pkt_num gid sid rev’, separator = ’\t’ }"
4.10 Shell
You must build with --enable-shell to make the command line shell available.
Enable shell mode:
snort --shell <args>
You will see the shell mode command prompt, which looks like this:
o")~
(The prompt can be changed with the SNORT_PROMPT environment variable.)
You can pause immediately after loading the configuration and again before exiting with:
snort --shell --pause <args>
In that case you must issue the resume() command to continue. Enter quit() to terminate Snort or detach() to exit the shell. You
can list the available commands with help().
To enable local telnet access on port 12345:
snort --shell -j 12345 <args>
The command line interface is still under development. Suggestions are welcome.
4.11 Signals
Note
The following examples assume that Snort is currently running and has a process ID of <pid>.
Modify and Reload Configuration:
echo ’suppress = { { gid = 1, sid = 2215 } }’ >> $my_path/etc/snort/snort.lua
kill -hup <pid>
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Dump stats to stdout:
kill -usr1 <pid>
Shutdown normally:
kill -term <pid>
Exit without flushing packets:
kill -quit <pid>
List available signals:
snort --help-signals
Note
The available signals may vary from platform to platform.
5 Features
This section explains how to use key features of Snort.
5.1 AppId
Network administrators need application awareness in order to fine tune their management of the ever-growing number of appli-
cations passing traffic over the network. Application awareness allows an administrator to create rules for applications as needed
by the business. The rules can be used to take action based on the application, such as block, allow or alert.
5.1.1 Overview
The AppId inspector provides an application level view when managing networks by providing the following features:
• Network control: The inspector works with Snort rules by providing a set of application identifiers (AppIds) to Snort rule
writers.
• Application usage awareness: The inspector outputs statistics to show how many times applications are being used on the
network.
• Custom applications: Administrators can create their own application detectors to detect new applications. The detectors are
written in Lua and interface with Snort using a well-defined C-Lua API.
• Open Detector Package (ODP): A set of pre-defined application detectors are provided by the Snort team and can be down-
loaded from snort.org.
5.1.2 Dependency Requirements
For proper functioning of the AppId inspector, at a minimum stream flow tracking must be enabled. In addition, to identify
TCP-based or UDP-based applications then the appropriate stream inspector must be enabled, e.g. stream_tcp or stream_udp.
In addition, in order to identify HTTP-based applications, the HTTP inspector must be enabled. Otherwise, only non-HTTP
applications will be identified.
AppId subscribes to the inspection events published by other inspectors, such as the HTTP and SSL inspectors, to gain access to
the data needed. It uses that data to help determine the application ID.
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5.1.3 Configuration
The AppId feature can be enabled via configuration. To enable it with the default settings use:
appid = { }
To use an AppId as a matching parameter in an IPS rule, use the appids keyword. For example, to block HTTP traffic that
contains a specific header:
block tcp any any -> 192.168.0.1 any ( msg:"Block Malicious HTTP header";
appids:"HTTP"; content:"X-Header: malicious"; sid:18000; )
Alternatively, the HTTP application can be specified in place of tcp instead of using the appids keyword. The AppId inspector
will set the service when it is discovered so it can be used in IPS rules like this. Note that this rule also does not specify the IPs
or ports which default to any.
block http ( msg:"Block Malicious HTTP header";
content:"X-Header: malicious"; sid:18000; )
It’s possible to specify multiple applications (as many as desired) with the appids keyword. A rule is considered a match if any
of the applications on the rule match. Note that this rule does not match specific content which will reduce performance.
alert tcp any any -> 192.168.0.1 any ( msg:"Alert ";
appids:"telnet,ssh,smtp,http";
Below is a minimal Snort configuration that is sufficient to block flows based on a specific HTTP header:
require("snort_config")
dir = os.getenv(’SNORT_LUA_PATH’)
if ( not dir ) then
dir = ’.’
end
dofile(dir .. ’/snort_defaults.lua’)
local_rules =
[[
block http ( msg:"openAppId: test content match for app http";
content:"X-Header: malicious"; sid:18760; rev:4; )
]]
stream = { }
stream_tcp = { }
binder =
{
{
when =
{
proto = ’tcp’,
ports = [[ 80 8080 ]],
},
use =
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{
type = ’http_inspect’,
},
},
}
http_inspect = { }
appid = { }
ips =
{
rules = local_rules,
}
5.1.4 Session Application Identifiers
There are up to four AppIds stored in a session as defined below:
• serviceAppId - An appId associated with server side of a session. Example: http server.
• clientAppId - An appId associated with application on client side of a session. Example: Firefox.
• payloadAppId - For services like http this appId is associated with a webserver host. Example: Facebook.
• miscAppId - For some encapsulated protocols, this is the highest encapsulated application.
For packets originating from the client, a payloadAppid in a session is matched with all AppIds listed on a rule. Thereafter
miscAppId, clientAppId and serviceAppId are matched. Since Alert Events contain one AppId, only the first match is reported.
If a rule without an appids option matches, then the most specific appId (in order of payload, misc, client, server) is reported.
The same logic is followed for packets originating from the server with one exception. The order of matching is changed to make
serviceAppId come before clientAppId.
5.1.5 AppId Usage Statistics
The AppId inspector prints application network usage periodically in the snort log directory in unified2 format. File name, time
interval for statistic and file rollover are controlled by appId inspection configuration.
5.1.6 Open Detector Package (ODP) Installation
Application detectors from Snort team will be delivered in a separate package called the Open Detector Package (ODP) that can
be downloaded from snort.org. ODP is a package that contains the following artifacts:
• Application detectors in the Lua language.
• Port detectors, which are port only application detectors, in meta-data in YAML format.
• appMapping.data file containing application metadata. This file should not be modified. The first column contains application
identifier and second column contains application name. Other columns contain internal information.
• Lua library files DetectorCommon.lua, flowTrackerModule.lua and hostServiceTrackerModule.lua
A user can install the ODP package in any directory and configure this directory via the app_detector_dir option in the appid
preprocessor configuration. Installing ODP will not modify any subdirectory named custom, where user-created detectors are
located.
When installed, ODP will create following sub-directories:
Snort 3 User Manual 27 / 284
• odp/port //Cisco port-only detectors
• odp/lua //Cisco Lua detectors
• odp/libs //Cisco Lua modules
5.1.7 User Created Application Detectors
Users can detect new applications by adding detectors in the Lua language. A document will be posted on the Snort Website
with details on API. Users can also copy over Snort team provided detectors and modify them. Users can also use the detector
creation tool described in the next section.
Users must organize their Lua detectors and libraries by creating the following directory structure, under the ODP installation
directory.
• custom/port //port-only detectors
• custom/lua //Lua detectors
• custom/libs //Lua modules
The root path is specified by the "app_detector_dir" parameter of the appid section of snort.conf:
appid =
{
app_detector_dir = ’/usr/local/lib/openappid’,
}
So the path to the user-created lua files would be /usr/local/lib/openappid/custom/lua/
None of the directories below /usr/local/lib/openappid/ would be added for you.
5.1.8 Application Detector Creation Tool
For rudimentary Lua detectors, there is a tool provided called appid_detector_builder.sh. This is a simple, menu-driven bash
script which creates .lua files in your current directory, based on your choices and on patterns you supply.
When you launch the script, it will prompt for the Application Id that you are giving for your detector. This is free-form ASCII
with minor restrictions. The Lua detector file will be named based on your Application Id. If the file name already exists you
will be prompted to overwrite it.
You will also be prompted for a description of your detector to be placed in the comments of the Lua source code. This is
optional.
You will then be asked a series of questions designed to construct Lua code based on the kind of pattern data, protocol, port(s),
etc.
When complete, the Protocol menu will be changed to include the option, "Save Detector". Instead of saving the file and exiting
the script, you are allowed to give additional criteria for another pattern which may also be incorporated in the detection scheme.
Then either pattern, when matched, will be considered a valid detection.
For example, your first choices might create an HTTP detection pattern of "example.com", and the next set of choices would add
the HTTP detection pattern of "example.uk.co" (an equally fictional British counterpart). They would then co-exist in the Lua
detector, and either would cause a detection with the name you give for your Application Id.
The resulting .lua file will need to be placed in the directory, "custom/lua", described in the previous section of the README
above called "User Created Application Detectors"
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5.2 Binder
One of the fundamental differences between Snort 2 and Snort 3 concerns configuration related to networks and ports. Here is a
brief review of Snort 2 configuration for network and service related components:
• Snort’s configuration has a default policy and optional policies selected by VLAN or network (with config binding).
• Each policy contains a user defined set of preprocessor configurations.
• Each preprocessor has a default configuration and some support non-default configurations selected by network.
• Most preprocessors have port configurations.
• The default policy may also contain a list of ports to ignore.
In Snort 3, the above configurations are done in a single module called the binder. Here is an example:
binder =
{
-- allow all tcp port 22:
-- (similar to Snort 2 config ignore_ports)
{ when = { proto = ’tcp’, ports = ’22’ }, use = { action = ’allow’ } },
-- select a config file by vlan
-- (similar to Snort 2 config binding by vlan)
{ when = { vlans = ’1024’ }, use = { file = ’vlan.lua’ } },
-- use a non-default HTTP inspector for port 8080:
-- (similar to a Snort 2 targeted preprocessor config)
{ when = { nets = ’192.168.0.0/16’, proto = ’tcp’, ports = ’8080’ },
use = { name = ’alt_http’, type = ’http_inspect’ } },
-- use the default inspectors:
-- (similar to a Snort 2 default preprocessor config)
{ when = { proto = ’tcp’ }, use = { type = ’stream_tcp’ } },
{ when = { service = ’http’ }, use = { type = ’http_inspect’ } },
-- figure out which inspector to run automatically:
{ use = { type = ’wizard’ } }
}
Bindings are evaluated when a session starts and again if and when service is identified on the session. Essentially, the bindings
are a list of when-use rules evaluated from top to bottom. The first matching network and service configurations are applied.
binder.when can contain any combination of criteria and binder.use can specify an action, config file, or inspector configuration.
5.3 Byte rule options
5.3.1 byte_test
This rule option tests a byte field against a specific value (with operator). Capable of testing binary values or converting repre-
sentative byte strings to their binary equivalent and testing them.
Snort uses the C operators for each of these operators. If the & operator is used, then it would be the same as using
if (data & value) { do_something(); }
Note: The bitmask option applies bitwise AND operator on the bytes converted. The result will be right-shifted by the number
of bits equal to the number of trailing zeros in the mask. This applies for the other rule options as well.
Snort 3 User Manual 29 / 284
Examples
alert tcp (byte_test:2, =, 568, 0, bitmask 0x3FF0;)
This example extracts 2 bytes at offset 0, performs bitwise and with bitmask 0x3FF0, shifts the result by 4 bits and compares to
568.
alert udp (byte_test:4, =, 1234, 0, string, dec;
msg:"got 1234!";)
alert udp (byte_test:8, =, 0xdeadbeef, 0, string, hex;
msg:"got DEADBEEF!";)
5.3.2 byte_jump
The byte_jump rule option allows rules to be written for length encoded protocols trivially. By having an option that reads the
length of a portion of data, then skips that far forward in the packet, rules can be written that skip over specific portions of
length-encoded protocols and perform detection in very specific locations.
Examples
alert tcp (content:"Begin";
byte_jump:0, 0, from_end, post_offset -6;
content:"end..", distance 0, within 5;
msg:"Content match from end of the payload";)
alert tcp (content:"catalog";
byte_jump:2, 1, relative, post_offset 2, bitmask 0x03f0;
byte_test:2, =, 968, 0, relative;
msg:"Bitmask applied on the 2 bytes extracted for byte_jump";)
5.3.3 byte_extract
The byte_extract keyword is another useful option for writing rules against length-encoded protocols. It reads in some number
of bytes from the packet payload and saves it to a variable. These variables can be referenced later in the rule, instead of using
hard-coded values.
Other options which use byte_extract variables
A byte_extract rule option detects nothing by itself. Its use is in extracting packet data for use in other rule options.
Here is a list of places where byte_extract variables can be used:
• content/uricontent: offset, depth, distance, within
• byte_test: offset, value
• byte_jump: offset
• isdataat: offset
Snort 3 User Manual 30 / 284
Examples
alert tcp (byte_extract:1, 0, str_offset;
byte_extract:1, 1, str_depth;
content:"bad stuff", offset str_offset, depth str_depth;
msg:"Bad Stuff detected within field";)
This example uses two variables.
The first variable keeps the offset of a string, read from a byte at offset 0. The second variable keeps the depth of a string, read
from a byte at offset 1. These values are used to constrain a pattern match to a smaller area.
alert tcp (content:"|04 63 34 35|", offset 4, depth 4;
byte_extract: 2, 0, var_match, relative, bitmask 0x03ff;
byte_test: 2, =, var_match, 2, relative;
msg:"Test value match, after applying bitmask on bytes extracted";)
5.3.4 byte_math
Perform a mathematical operation on an extracted value and a specified value or existing variable, and store the outcome in a
new resulting variable. These resulting variables can be referenced later in the rule, at the same places as byte_extract variables.
The syntax for this rule option is different. The order of the options is critical for the other rule options and can’t be changed. For
example, the first option is the number of bytes to extract. Here the name of the option is explicitly written, for example : bytes
2. The order is not important.
Note
Byte_math operations are performed on unsigned 32-bit values. When writing a rule it should be taken into consideration to
avoid wrap around.
Examples
alert tcp ( byte_math: bytes 2, offset 0, oper *, rvalue 10, result area;
byte_test:2,>,area,16;)
At the zero offset of the payload, extract 2 bytes and apply multiplication operation with value 10. Store result in variable area.
The area variable is given as input to byte_test value option.
Let’s consider 2 bytes of extracted data is 5. The rvalue is 10. Result variable area is 50 ( 5 * 10 ). Area variable can be used in
either byte_test offset/value options.
5.3.5 Testing Numerical Values
The rule options byte_test and byte_jump were written to support writing rules for protocols that have length encoded data. RPC
was the protocol that spawned the requirement for these two rule options, as RPC uses simple length based encoding for passing
data.
In order to understand why byte test and byte jump are useful, let’s go through an exploit attempt against the sadmind service.
This is the payload of the exploit:
89 09 9c e2 00 00 00 00 00 00 00 02 00 01 87 88 ................
00 00 00 0a 00 00 00 01 00 00 00 01 00 00 00 20 ...............
40 28 3a 10 00 00 00 0a 4d 45 54 41 53 50 4c 4f @(:.....metasplo
49 54 00 00 00 00 00 00 00 00 00 00 00 00 00 00 it..............
00 00 00 00 00 00 00 00 40 28 3a 14 00 07 45 df ........@(:...e.
Snort 3 User Manual 31 / 284
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 06 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 04 00 00 00 00 00 00 00 04 ................
7f 00 00 01 00 01 87 88 00 00 00 0a 00 00 00 04 ................
7f 00 00 01 00 01 87 88 00 00 00 0a 00 00 00 11 ................
00 00 00 1e 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 3b 4d 45 54 41 53 50 4c 4f .......;metasplo
49 54 00 00 00 00 00 00 00 00 00 00 00 00 00 00 it..............
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 06 73 79 73 74 65 6d 00 00 ........system..
00 00 00 15 2e 2e 2f 2e 2e 2f 2e 2e 2f 2e 2e 2f ....../../../../
2e 2e 2f 62 69 6e 2f 73 68 00 00 00 00 00 04 1e ../bin/sh.......
Let’s break this up, describe each of the fields, and figure out how to write a rule to catch this exploit.
There are a few things to note with RPC:
Numbers are written as uint32s, taking four bytes. The number 26 would show up as 0x0000001a.
Strings are written as a uint32 specifying the length of the string, the string, and then null bytes to pad the length of the string to
end on a 4-byte boundary. The string bob would show up as 0x00000003626f6200.
89 09 9c e2 - the request id, a random uint32, unique to each request
00 00 00 00 - rpc type (call = 0, response = 1)
00 00 00 02 - rpc version (2)
00 01 87 88 - rpc program (0x00018788 = 100232 = sadmind)
00 00 00 0a - rpc program version (0x0000000a = 10)
00 00 00 01 - rpc procedure (0x00000001 = 1)
00 00 00 01 - credential flavor (1 = auth_unix)
00 00 00 20 - length of auth_unix data (0x20 = 32)
## the next 32 bytes are the auth_unix data
40 28 3a 10 - unix timestamp (0x40283a10 = 1076378128 = feb 10 01:55:28 2004 gmt)
00 00 00 0a - length of the client machine name (0x0a = 10)
4d 45 54 41 53 50 4c 4f 49 54 00 00 - metasploit
00 00 00 00 - uid of requesting user (0)
00 00 00 00 - gid of requesting user (0)
00 00 00 00 - extra group ids (0)
00 00 00 00 - verifier flavor (0 = auth_null, aka none)
00 00 00 00 - length of verifier (0, aka none)
The rest of the packet is the request that gets passed to procedure 1 of sadmind.
However, we know the vulnerability is that sadmind trusts the uid coming from the client. sadmind runs any request where the
client’s uid is 0 as root. As such, we have decoded enough of the request to write our rule.
First, we need to make sure that our packet is an RPC call.
content:"|00 00 00 00|", offset 4, depth 4;
Then, we need to make sure that our packet is a call to sadmind.
content:"|00 01 87 88|", offset 12, depth 4;
Then, we need to make sure that our packet is a call to the procedure 1, the vulnerable procedure.
Snort 3 User Manual 32 / 284
content:"|00 00 00 01|", offset 20, depth 4;
Then, we need to make sure that our packet has auth_unix credentials.
content:"|00 00 00 01|", offset 24, depth 4;
We don’t care about the hostname, but we want to skip over it and check a number value after the hostname. This is where
byte_test is useful. Starting at the length of the hostname, the data we have is:
00 00 00 0a 4d 45 54 41 53 50 4c 4f 49 54 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00
We want to read 4 bytes, turn it into a number, and jump that many bytes forward, making sure to account for the padding that
RPC requires on strings. If we do that, we are now at:
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00
which happens to be the exact location of the uid, the value we want to check.
In English, we want to read 4 bytes, 36 bytes from the beginning of the packet, and turn those 4 bytes into an integer and jump
that many bytes forward, aligning on the 4-byte boundary. To do that in a Snort rule, we use:
byte_jump:4,36,align;
then we want to look for the uid of 0.
content:"|00 00 00 00|", within 4;
Now that we have all the detection capabilities for our rule, let’s put them all together.
content:"|00 00 00 00|", offset 4, depth 4;
content:"|00 01 87 88|", offset 12, depth 4;
content:"|00 00 00 01|", offset 20, depth 4;
content:"|00 00 00 01|", offset 24, depth 4;
byte_jump:4,36,align;
content:"|00 00 00 00|", within 4;
The 3rd and fourth string match are right next to each other, so we should combine those patterns. We end up with:
content:"|00 00 00 00|", offset 4, depth 4;
content:"|00 01 87 88|", offset 12, depth 4;
content:"|00 00 00 01 00 00 00 01|", offset 20, depth 8;
byte_jump:4,36,align;
content:"|00 00 00 00|", within 4;
If the sadmind service was vulnerable to a buffer overflow when reading the client’s hostname, instead of reading the length of
the hostname and jumping that many bytes forward, we would check the length of the hostname to make sure it is not too large.
To do that, we would read 4 bytes, starting 36 bytes into the packet, turn it into a number, and then make sure it is not too large
(let’s say bigger than 200 bytes). In Snort, we do:
byte_test:4,>,200,36;
Our full rule would be:
content:"|00 00 00 00|", offset 4, depth 4;
content:"|00 01 87 88|", offset 12, depth 4;
content:"|00 00 00 01 00 00 00 01|", offset 20, depth 8;
byte_test:4,>,200,36;
Snort 3 User Manual 33 / 284
5.4 DCE Inspectors
The main purpose of these inspector are to perform SMB desegmentation and DCE/RPC defragmentation to avoid rule evasion
using these techniques.
5.4.1 Overview
The following transports are supported for DCE/RPC: SMB, TCP, and UDP. New rule options have been implemented to improve
performance, reduce false positives and reduce the count and complexity of DCE/RPC based rules.
Different from Snort 2, the DCE-RPC preprocessor is split into three inspectors - one for each transport: dce_smb, dce_tcp,
dce_udp. This includes the configuration as well as the inspector modules. The Snort 2 server configuration is now split between
the inspectors. Options that are meaningful to all inspectors, such as policy and defragmentation, are copied into each inspector
configuration. The address/port mapping is handled by the binder. Autodetect functionality is replaced by wizard curses.
5.4.2 Quick Guide
A typical dcerpce configuration looks like this:
binder =
{
{
when =
{
proto = ’tcp’,
ports = ’139 445 1025’,
},
use =
{
type = ’dce_smb’,
},
},
{
when =
{
proto = ’tcp’,
ports = ’135 2103’,
},
use =
{
type = ’dce_tcp’,
},
},
{
when =
{
proto = ’udp’,
ports = ’1030’,
},
use =
{
type = ’dce_udp’,
},
}
}
Snort 3 User Manual 34 / 284
dce_smb = { }
dce_tcp = { }
dce_udp = { }
In this example, it defines smb, tcp and udp inspectors based on port. All the configurations are default.
5.4.3 Target Based
There are enough important differences between Windows and Samba versions that a target based approach has been imple-
mented. Some important differences:
• Named pipe instance tracking
• Accepted SMB commands
• AndX command chaining
• Transaction tracking
• Multiple Bind requests
• DCE/RPC Fragmented requests - Context ID
• DCE/RPC Fragmented requests - Operation number
• DCE/RPC Stub data byte order
Because of those differences, each inspector can be configured to different policy. Here are the list of policies supported:
• WinXP (default)
• Win2000
• WinVista
• Win2003
• Win2008
• Win7
• Samba
• Samba-3.0.37
• Samba-3.0.22
• Samba-3.0.20
5.4.4 Reassembling
Both SMB inspector and TCP inspector support reassemble. Reassemble threshold specifies a minimum number of bytes in the
DCE/RPC desegmentation and defragmentation buffers before creating a reassembly packet to send to the detection engine. This
option is useful in inline mode so as to potentially catch an exploit early before full defragmentation is done. A value of 0 s
supplied as an argument to this option will, in effect, disable this option. Default is disabled.
Snort 3 User Manual 35 / 284
5.4.5 SMB
SMB inspector is one of the most complex inspectors. In addition to supporting rule options and lots of inspector rule events, it
also supports file processing for both SMB version 1, 2, and 3.
Finger Print Policy
In the initial phase of an SMB session, the client needs to authenticate with a SessionSetupAndX. Both the request and response
to this command contain OS and version information that can allow the inspector to dynamically set the policy for a session
which allows for better protection against Windows and Samba specific evasions.
File Inspection
SMB inspector supports file inspection. A typical configuration looks like this:
binder =
{
{
when =
{
proto = ’tcp’,
ports = ’139 445’,
},
use =
{
type = ’dce_smb’,
},
},
}
dce_smb =
{
smb_file_inspection = ’on’,
smb_file_depth = 0,
}
file_id =
{
enable_type = true,
enable_signature = true,
enable_capture = true,
file_rules = magics,
}
First, define a binder to map tcp port 139 and 445 to smb. Then, enable file inspection in smb inspection and set the file depth as
unlimited. Lastly, enable file inspector to inspect file type, calculate file signature, and capture file. The details of file inspector
are explained in file processing section.
SMB inspector does inspection of normal SMB file transfers. This includes doing file type and signature through the file pro-
cessing as well as setting a pointer for the "file_data" rule option. Note that the "file_depth" option only applies to the maximum
amount of file data for which it will set the pointer for the "file_data" rule option. For file type and signature it will use the
value configured for the file API. If "only" is specified, the inspector will only do SMB file inspection, i.e. it will not do any
DCE/RPC tracking or inspection. If "on" is specified with no arguments, the default file depth is 16384 bytes. An argument of
-1 to "file-depth" disables setting the pointer for "file_data", effectively disabling SMB file inspection in rules. An argument of 0
to "file_depth" means unlimited. Default is "off", i.e. no SMB file inspection is done in the inspector.
Snort 3 User Manual 36 / 284
5.4.6 TCP
dce_tcp inspector supports defragmentation, reassembling, and policy that is similar to SMB.
5.4.7 UDP
dce_udp is a very simple inspector that only supports defragmentation
5.4.8 Rule Options
New rule options are supported by enabling the dcerpc2 inspectors:
• dce_iface
• dce_opnum
• dce_stub_data
New modifiers to existing byte_test and byte_jump rule options:
• byte_test: dce
• byte_jump: dce
dce_iface
For DCE/RPC based rules it has been necessary to set flow-bits based on a client bind to a service to avoid false positives. It is
necessary for a client to bind to a service before being able to make a call to it. When a client sends a bind request to the server,
it can, however, specify one or more service interfaces to bind to. Each interface is represented by a UUID. Each interface UUID
is paired with a unique index (or context id) that future requests can use to reference the service that the client is making a call to.
The server will respond with the interface UUIDs it accepts as valid and will allow the client to make requests to those services.
When a client makes a request, it will specify the context id so the server knows what service the client is making a request
to. Instead of using flow-bits, a rule can simply ask the inspector, using this rule option, whether or not the client has bound
to a specific interface UUID and whether or not this client request is making a request to it. This can eliminate false positives
where more than one service is bound to successfully since the inspector can correlate the bind UUID to the context id used in
the request. A DCE/RPC request can specify whether numbers are represented as big endian or little endian. The representation
of the interface UUID is different depending on the endianness specified in the DCE/RPC previously requiring two rules - one
for big endian and one for little endian. The inspector eliminates the need for two rules by normalizing the UUID. An interface
contains a version. Some versions of an interface may not be vulnerable to a certain exploit. Also, a DCE/RPC request can be
broken up into 1 or more fragments. Flags (and a field in the connectionless header) are set in the DCE/RPC header to indicate
whether the fragment is the first, a middle or the last fragment. Many checks for data in the DCE/RPC request are only relevant if
the DCE/RPC request is a first fragment (or full request), since subsequent fragments will contain data deeper into the DCE/RPC
request. A rule which is looking for data, say 5 bytes into the request (maybe it’s a length field), will be looking at the wrong data
on a fragment other than the first, since the beginning of subsequent fragments are already offset some length from the beginning
of the request. This can be a source of false positives in fragmented DCE/RPC traffic. By default it is reasonable to only evaluate
if the request is a first fragment (or full request). However, if the "any_frag" option is used to specify evaluating on all fragments.
Examples:
dce_iface: 4b324fc8-1670-01d3-1278-5a47bf6ee188;
dce_iface: 4b324fc8-1670-01d3-1278-5a47bf6ee188,<2;
dce_iface: 4b324fc8-1670-01d3-1278-5a47bf6ee188,any_frag;
dce_iface: 4b324fc8-1670-01d3-1278-5a47bf6ee188,=1,any_frag;
Snort 3 User Manual 37 / 284
This option is used to specify an interface UUID. Optional arguments are an interface version and operator to specify that the
version be less than (<), greater than (>), equal to (=) or not equal to (!) the version specified. Also, by default the rule will
only be evaluated for a first fragment (or full request, i.e. not a fragment) since most rules are written to start at the beginning of
a request. The "any_frag" argument says to evaluate for middle and last fragments as well. This option requires tracking client
Bind and Alter Context requests as well as server Bind Ack and Alter Context responses for connection-oriented DCE/RPC in
the inspector. For each Bind and Alter Context request, the client specifies a list of interface UUIDs along with a handle (or
context id) for each interface UUID that will be used during the DCE/RPC session to reference the interface. The server response
indicates which interfaces it will allow the client to make requests to - it either accepts or rejects the client’s wish to bind to a
certain interface. This tracking is required so that when a request is processed, the context id used in the request can be correlated
with the interface UUID it is a handle for.
hexlong and hexshort will be specified and interpreted to be in big endian order (this is usually the default way an interface UUID
will be seen and represented). As an example, the following Messenger interface UUID as taken off the wire from a little endian
Bind request:
|f8 91 7b 5a 00 ff d0 11 a9 b2 00 c0 4f b6 e6 fc|
must be written as:
5a7b91f8-ff00-11d0-a9b2-00c04fb6e6fc
The same UUID taken off the wire from a big endian Bind request:
|5a 7b 91 f8 ff 00 11 d0 a9 b2 00 c0 4f b6 e6 fc|
must be written the same way:
5a7b91f8-ff00-11d0-a9b2-00c04fb6e6fc
This option matches if the specified interface UUID matches the interface UUID (as referred to by the context id) of the DCE/RPC
request and if supplied, the version operation is true. This option will not match if the fragment is not a first fragment (or full
request) unless the "any_frag" option is supplied in which case only the interface UUID and version need match. Note that a
defragmented DCE/RPC request will be considered a full request.
Using this rule option will automatically insert fast pattern contents into the fast pattern matcher. For UDP rules, the inter-
face UUID, in both big and little endian format will be inserted into the fast pattern matcher. For TCP rules, (1) if the rule
option "flow:to_server|from_client" is used, |05 00 00| will be inserted into the fast pattern matcher, (2) if the rule option
"flow:from_server|to_client" is used, |05 00 02| will be inserted into the fast pattern matcher and (3) if the flow isn’t known,
|05 00| will be inserted into the fast pattern matcher. Note that if the rule already has content rule options in it, the best (meaning
longest) pattern will be used. If a content in the rule uses the fast_pattern rule option, it will unequivocally be used over the above
mentioned patterns.
dce_opnum
The opnum represents a specific function call to an interface. After is has been determined that a client has bound to a specific
interface and is making a request to it (see above - dce_iface) usually we want to know what function call it is making to that
service. It is likely that an exploit lies in the particular DCE/RPC function call.
Examples:
dce_opnum: 15;
dce_opnum: 15-18;
dce_opnum: 15,18-20;
dce_opnum: 15,17,20-22;
This option is used to specify an opnum (or operation number), opnum range or list containing either or both opnum and/or
opnum-range. The opnum of a DCE/RPC request will be matched against the opnums specified with this option. This option
matches if any one of the opnums specified match the opnum of the DCE/RPC request.
Snort 3 User Manual 38 / 284
dce_stub_data
Since most DCE/RPC based rules had to do protocol decoding only to get to the DCE/RPC stub data, i.e. the remote procedure
call or function call data, this option will alleviate this need and place the cursor at the beginning of the DCE/RPC stub data. This
reduces the number of rule option checks and the complexity of the rule.
This option takes no arguments.
Example:
dce_stub_data;
This option is used to place the cursor (used to walk the packet payload in rules processing) at the beginning of the DCE/RPC
stub data, regardless of preceding rule options. There are no arguments to this option. This option matches if there is DCE/RPC
stub data.
The cursor is moved to the beginning of the stub data. All ensuing rule options will be considered "sticky" to this buffer. The first
rule option following dce_stub_data should use absolute location modifiers if it is position-dependent. Subsequent rule options
should use a relative modifier if they are meant to be relative to a previous rule option match in the stub data buffer. Any rule
option that does not specify a relative modifier will be evaluated from the start of the stub data buffer. To leave the stub data
buffer and return to the main payload buffer, use the "pkt_data" rule option.
byte_test and byte_jump
A DCE/RPC request can specify whether numbers are represented in big or little endian. These rule options will take as a new
argument "dce" and will work basically the same as the normal byte_test/byte_jump, but since the DCE/RPC inspector will know
the endianness of the request, it will be able to do the correct conversion.
Examples:
byte_test: 4,>,35000,0,relative,dce;
byte_test: 2,!=,2280,-10,relative,dce;
When using the "dce" argument to a byte_test, the following normal byte_test arguments will not be allowed: "big", "little",
"string", "hex", "dec" and "oct".
Examples:
byte_jump:4,-4,relative,align,multiplier 2,post_offset -4,dce;
When using the dce argument to a byte_jump, the following normal byte_jump arguments will not be allowed: "big", "little",
"string", "hex", "dec", "oct" and "from_beginning"
5.5 File Processing
With the volume of malware transferred through network increasing, network file inspection becomes more and more important.
This feature will provide file type identification, file signature creation, and file capture capabilities to help users deal with those
challenges.
5.5.1 Overview
There are two parts of file services: file APIs and file policy. File APIs provides all the file inspection functionalities, such as file
type identification, file signature calculation, and file capture. File policy provides users ability to control file services, such as
enable/disable/configure file type identification, file signature, or file capture.
In addition to all capabilities from Snort 2, we support customized file policy along with file event log.
• Supported protocols: HTTP, SMTP, IMAP, POP3, FTP, and SMB.
• Supported file signature calculation: SHA256
Snort 3 User Manual 39 / 284
5.5.2 Quick Guide
A very simple configuration has been included in lua/snort.lua file. A typical file configuration looks like this:
dofile(’magic.lua’)
my_file_policy =
{
{ when = { file_type_id = 0 }, use = { verdict = ’log’, enable_file_signature ←-
= true, enable_file_capture = true } }
{ when = { file_type_id = 22 }, use = { verdict = ’log’, ←-
enable_file_signature = true } },
{ when = { sha256 = " ←-
F74DC976BC8387E7D4FC0716A069017A0C7ED13F309A523CC41A8739CCB7D4B6" }, use = ←-
{ verdict = ’block’} },
}
file_id =
{
enable_type = true,
enable_signature = true,
enable_capture = true,
file_rules = magics,
trace_type = true,
trace_signature = true,
trace_stream = true,
file_policy = my_file_policy,
}
file_log =
{
log_pkt_time = true,
log_sys_time = false,
}
There are 3 steps to enable file processing:
• First, you need to include the file magic rules.
• Then, define the file policy and configure the inspector
• At last, enable file_log to get detailed information about file event
5.5.3 Pre-packaged File Magic Rules
A set of file magic rules is packaged with Snort. They can be located at "lua/file_magic.lua". To use this feature, it is recom-
mended that these pre-packaged rules are used; doing so requires that you include the file in your Snort configuration as such
(already in snort.lua):
dofile(’magic.lua’)
Example:
{ type = "GIF", id = 62, category = "Graphics", rev = 1,
magic = { { content = "| 47 49 46 38 37 61 |",offset = 0 } } },
Snort 3 User Manual 40 / 284
{ type = "GIF", id = 63, category = "Graphics", rev = 1,
magic = { { content = "| 47 49 46 38 39 61 |",offset = 0 } } },
The previous two rules define GIF format, because two file magics are different. File magics are specified by content and offset,
which look at content at particular file offset to identify the file type. In this case, two magics look at the beginning of the file.
You can use character if it is printable or hex value in between "|".
5.5.4 File Policy
You can enabled file type, file signature, or file capture by configuring file_id. In addition, you can enable trace to see file stream
data, file type, and file signature information.
Most importantly, you can configure a file policy that can block/alert some file type or an individual file based on SHA. This
allows you build a file blacklist or whitelist.
Example:
file_policy =
{
{ when = { file_type_id = 22 }, use = { verdict = ’log’, ←-
enable_file_signature = true } },
{ when = { sha256 = " ←-
F74DC976BC8387E7D4FC0716A069017A0C7ED13F309A523CC41A8739CCB7D4B6" }, use = ←-
{ verdict = ’block’} },
{ when = { file_type_id = 0 }, use = { verdict = ’log’, enable_file_signature ←-
= true, enable_file_capture = true } }
}
In this example, it enables this policy:
• For PDF files, they will be logged with signatures.
• For the file matching this SHA, it will be blocked
• For all file types identified, they will be logged with signature, and also captured onto log folder.
5.5.5 File Capture
File can be captured and stored to log folder. We use SHA as file name instead of actual file name to avoid conflicts. You can
capture either all files, some file type, or a particular file based on SHA.
You can enable file capture through this config:
enable_capture = true,
or enable it for some file or file type in your file policy:
{ when = { file_type_id = 22 }, use = { verdict = ’log’, enable_file_capture = ←-
true } },
The above rule will enable PDF file capture.
Snort 3 User Manual 41 / 284
5.5.6 File Events
File inspect preprocessor also works as a dynamic output plugin for file events. It logs basic information about file. The log file
is in the same folder as other log files with name starting with "file.log".
Example:
file_log = { log_pkt_time = true, log_sys_time = false }
All file events will be logged in packet time, system time is not logged.
File event example:
08/14-19:14:19.100891 10.22.75.72:33734 -> 10.22.75.36:80,
[Name: "malware.exe"] [Verdict: Block] [Type: MSEXE]
[SHA: 6F26E721FDB1AAFD29B41BCF90196DEE3A5412550615A856DAE8E3634BCE9F7A]
[Size: 1039328]
5.6 High Availability
High Availability includes the HA flow synchronization and the SideChannel messaging subsystems.
5.6.1 HA
HighAvailability (or HA) is a Snort module that provides state coherency between two partner snort instances. It uses SideChan-
nel for messaging.
There can be multiple types of HA within Snort and Snort plugins. HA implements an extensible architecture to enable plugins
to subscribe to the base flow HA messaging. These plugins can then include their own messages along with the flow cache HA
messages.
HA produces and consumes two type of messages:
• Update - Update flow status. Plugins may add their own data to the messages
• Delete - A flow has been removed from the cache
The HA module is configured with these items:
high_availability =
{
ports = "1",
enable = true,
min_age = 0.0,
min_sync = 0.0
}
The ports item maps to the SideChannel port to use for the HA messaging.
The enabled item controls the overall HA operation.
The items min_age and min_sync are used in the stream HA logic. min_age is the number of seconds that a flow must exist
in the flow cache before sending HA messages to the partner. min_sync is the minimum time between HA status updates. HA
messages for a particular flow will not be sent faster than min_sync. Both are expressed as a floating point number of seconds.
HA messages are composed of the base stream information plus any content from additional modules. Modules subscribe HA
in order to add message content. The stream HA content is always present in the messages while the ancillary module content is
only present when requested via a status change request.
Snort 3 User Manual 42 / 284
5.6.2 Connector
Connectors are a set of modules that are used to exchange message-oriented data among Snort threads and the external world.
A typical use-case is HA (High Availability) message exchange. Connectors serve to decouple the message transport from the
message creation/consumption. Connectors expose a common API for several forms of message transport.
Connectors are a Snort plugin type.
Connector (parent plugin class)
Connectors may either be a simplex channel and perform unidirectional communications. Or may be duplex and perform bidi-
rectional communications. The TcpConnector is duplex while the FileConnector is simplex.
All subtypes of Connector have a direction configuration element and a connector element. The connector string is the key used to
identify the element for sidechannel configuration. The direction element may have a default value, for instance TcpConnector’s
are duplex.
There are currently two implementations of Connectors:
• TcpConnector - Exchange messages over a tcp channel.
• FileConnector - Write messages to files and read messages from files.
TcpConnector
TcpConnector is a subclass of Connector and implements a DUPLEX type Connector, able to send and receive messages over a
tcp session.
TcpConnector adds a few session setup configuration elements:
• setup = call or answer -call is used to have TcpConnector initiate the connection. answer is used to have TcpConnector accept
incoming connections.
• address = <addr> - used for call setup to specify the partner
• base_port = port - used to contruct the actual port number for call and answer modes. Actual port used is (base_port +
instance_id).
An example segment of TcpConnector configuration:
tcp_connector =
{
{
connector = ’tcp_1’,
address = ’127.0.0.1’,
setup = ’call’,
base_port = 11000
},
}
FileConnector
FileConnector implements a Connector that can either read from files or write to files. FileConnector’s are simplex and must be
configured to be CONN_TRANSMIT or CONN_RECEIVE.
FileConnector configuration adds two additional element:
• name = string - used as part of the message file name
Snort 3 User Manual 43 / 284
• format = text or binary - FileConnector supports two file types
The configured name string is used to construct the actual names as in:
• file_connector_NAME_transmit and file_connector_NAME_receive
All messages for one Snort invocation are read and written to one file.
In the case of a receive FileConnector, all messages are read from the file prior to the start of packet processing. This allows the
messages to establish state information for all processed packets.
Connectors are used solely by SideChannel
An example segment of FileConnector configuration:
file_connector =
{
{
connector = ’file_tx_1’,
direction = ’transmit’,
format = ’text’,
name = ’HA’
},
{
connector = ’file_rx_1’,
direction = ’receive’,
format = ’text’,
name = ’HA’
},
}
5.6.3 Side Channel
SideChannel is a Snort module that uses Connectors to implement a messaging infrastructure that is used to communicate between
Snort threads and the outside world.
SideChannel adds functionality onto the Connector as:
• message multiplexing/demultiplexing - An additional protocol layer is added to the messages. This port number is used to
direct message to/from various SideClass instancs.
• application receive processing - handler for received messages on a specific port.
SideChannel’s are always implement a duplex (bidirectional) messaging model and can map to separate transmit and receive
Connectors.
The message handling model leverages the underlying Connector handling. So please refer to the Connector documentation.
SideChannel’s are instantiated by various applications. The SideChannel port numbers are the configuration element used to map
SideChannel’s to applications.
The SideChannel configuration mostly serves to map a port number to a Connector or set of connectors. Each port mapping can
have at most one transmit plus one receive connector or one duplex connector. Multiple SideChannel’s may be configured and
instantiated to support multiple applications.
An example SideChannel configuration along with the corresponding Connector configuration:
side_channel =
{
{
Snort 3 User Manual 44 / 284
ports = ’1’,
connectors =
{
{
connector = ’file_rx_1’,
},
{
connector = ’file_tx_1’,
}
},
},
}
file_connector =
{
{
connector = ’file_tx_1’,
direction = ’transmit’,
format = ’text’,
name = ’HA’
},
{
connector = ’file_rx_1’,
direction = ’receive’,
format = ’text’,
name = ’HA’
},
}
5.7 HTTP Inspector
One of the major undertakings for Snort 3 is developing a completely new HTTP inspector.
5.7.1 Overview
You can configure it by adding:
http_inspect = {}
to your snort.lua configuration file. Or you can read about it in the source code under src/service_inspectors/http_inspect.
The classic HTTP preprocessor is still available in the alpha release under extra. It has been renamed http_server. Be sure not to
configure both old and new HTTP inspectors at the same time.
So why a new HTTP inspector?
For starters it is object-oriented. That’s good for us because we maintain this software. But it should also be really nice for
open-source developers. You can make meaningful changes and additions to HTTP processing without having to understand the
whole thing. In fact much of the new HTTP inspector’s knowledge of HTTP is centralized in a series of tables where it can be
easily reviewed and modified. Many significant changes can be made just by updating these tables.
http_inspect is the first inspector written specifically for the new Snort 3 architecture. This provides access to one of the very best
features of Snort 3: purely PDU-based inspection. The classic preprocessor processes HTTP messages, but even while doing so
it is constantly aware of IP packets and how they divide up the TCP data stream. The same HTTP message might be processed
differently depending on how the sender (bad guy) divided it up into IP packets.
Snort 3 User Manual 45 / 284
http_inspect is free of this burden and can focus exclusively on HTTP. This makes it much simpler, easier to test, and less prone
to false positives. It also greatly reduces the opportunity for adversaries to probe the inspector for weak spots by adjusting packet
boundaries to disguise bad behavior.
Dealing solely with HTTP messages also opens the door for developing major new features. The http_inspect design supports
true stateful processing. Want to ask questions that involve both the client request and the server response? Or different requests
in the same session? These things are possible.
Another new feature on the horizon is HTTP/2 analysis. HTTP/2 derives from Google’s SPDY project and is in the process of
being standardized. Despite the name, it is better to think of HTTP/2 not as a newer version of HTTP/1.1, but rather a separate
protocol layer that runs under HTTP/1.1 and on top of TLS or TCP. It’s a perfect fit for the new Snort 3 architecture because a
new HTTP/2 inspector would naturally output HTTP/1.1 messages but not any underlying packets. Exactly what http_inspect
wants to input.
http_inspect is taking a very different approach to HTTP header fields. The classic preprocessor divides all the HTTP headers
following the start line into cookies and everything else. It normalizes the two pieces using a generic process and puts them in
buffers that one can write rules against. There is some limited support for examining individual headers within the inspector but
it is very specific.
The new concept is that every header should be normalized in an appropriate and specific way and individually made available
for the user to write rules against it. If for example a header is supposed to be a date then normalization means put that date in a
standard format.
5.7.2 Configuration
Configuration can be as simple as adding:
http_inspect = {}
to your snort.lua file. The default configuration provides a thorough inspection and may be all that you need. But there are some
options that provide extra features, tweak how things are done, or conserve resources by doing less.
request_depth and response_depth
These replace the flow depth parameters used by the old HTTP inspector but they work differently.
The default is to inspect the entire HTTP message body. That’s a very sound approach but if your HTTP traffic includes many very
large files such as videos the load on Snort can become burdensome. Setting the request_depth and response_depth parameters
will limit the amount of body data that is sent to the rule engine. For example:
request_depth = 10000,
response_depth = 80000,
would examine only the first 10000 bytes of POST, PUT, and other message bodies sent by the client. Responses from the server
would be limited to 80000 bytes.
These limits apply only to the message bodies. HTTP headers are always completely inspected.
If you want to only inspect headers and no body, set the depth to 0. If you want to inspect the entire body set the depth to -1 or
simply omit the depth parameter entirely because that is the default.
These limits have no effect on how much data is forwarded to file processing.
gzip
http_inspect by default decompresses deflate and gzip message bodies before inspecting them. This feature can be turned off by
unzip = false. Turning off decompression provides a substantial performance improvement but at a very high price. It is unlikely
that any meaningful inspection of message bodies will be possible. Effectively HTTP processing would be limited to the headers.
Snort 3 User Manual 46 / 284
normalize_utf
http_inspect will decode utf-8, utf-7, utf-16le, utf-16be, utf-32le, and utf-32be in response message bodies based on the Content-
Type header. This feature is on by default: normalize_utf = false will deactivate it.
decompress_pdf
decompress_pdf = true will enable decompression of compressed portions of PDF files encountered in a response body. http_inspect
will examine the response body for PDF files that are then parsed to locate PDF streams with a single /FlateDecode filter. The
compressed content is decompressed and made available through the file data rule option.
decompress_swf
decompress_swf = true will enable decompression of compressed SWF (Adobe Flash content) files encountered in a response
body. The available decompression modes are ’deflate’ and ’lzma’. http_inspect will search for the file signatures CWS for
Deflate/ZLIB and ZWS for LZMA. The compressed content is decompressed and made available through the file data rule
option. The compressed SWF file signature is converted to FWS to indicate an uncompressed file.
normalize_javascript
normalize_javascript = true will enable normalization of JavaScript within the HTTP response body. http_inspect looks for
JavaScript by searching for the <script> tag without a type. Obfuscated data within the JavaScript functions such as unescape,
String.fromCharCode, decodeURI, and decodeURIComponent are normalized. The different encodings handled within the un-
escape, decodeURI, or decodeURIComponent are %XX, %uXXXX, XX and uXXXXi. http_inspect also replaces consecutive
whitespaces with a single space and normalizes the plus by concatenating the strings.
URI processing
Normalization and inspection of the URI in the HTTP request message is a key aspect of what http_inspect does. The best way
to normalize a URI is very dependent on the idiosyncrasies of the HTTP server being accessed. The goal is to interpret the URI
the same way as the server will so that nothing the server will see can be hidden from the rule engine.
The default URI inspection parameters are oriented toward following the HTTP RFCs—reading the URI the way the standards
say it should be read. Most servers deviate from this ideal in various ways that can be exploited by an attacker. The options
provide tools for the user to cope with that.
utf8 = true
plus_to_space = true
percent_u = false
utf8_bare_byte = false
iis_unicode = false
iis_double_decode = false
The HTTP inspector normalizes percent encodings found in URIs. For instance it will convert "%48%69%64%64%65%6e" to
"Hidden". All the options listed above control how this is done. The options listed as true are fairly standard features that are
decoded by default. You don’t need to list them in snort.lua unless you want to turn them off by setting them to false. But that is
not recommended unless you know what you are doing and have a definite reason.
The other options are primarily for the protection of servers that support irregular forms of decoding. These features are off by
default but you can activate them if you need to by setting them to true in snort.lua.
bad_characters = "0x25 0x7e 0x6b 0x80 0x81 0x82 0x83 0x84"
That’s a list of 8-bit Ascii characters that you don’t want present in any normalized URI after the percent decoding is done. For
example 0x25 is a hexadecimal number (37 in decimal) which stands for the %character. The % character is legitimately used
for encoding special characters in a URI. But if there is still a percent after normalization one might conclude that something is
wrong. If you choose to configure 0x25 as a bad character there will be an alert whenever this happens.
Snort 3 User Manual 47 / 284
Another example is 0x00 which signifies the null character zero. Null characters in a URI are generally wrong and very suspi-
cious.
The default is not to alert on any of the 256 8-bit Ascii characters. Add this option to your configuration if you want to define
some bad characters.
ignore_unreserved = "abc123"
Percent encoding common characters such as letters and numbers that have no special meaning in HTTP is suspicious. It’s legal
but why would you do it unless you have something to hide? http_inspect will alert whenever an upper-case or lower-case letter,
a digit, period, underscore, tilde, or minus is percent-encoded. But if a legitimate application in your environment encodes some
of these characters for some reason this allows you to create exemptions for those characters.
In the example, the lower-case letters a, b, and c and the digits 1, 2, and 3 are exempted. These may be percent-encoded without
generating an alert.
simplify_path = true
backslash_to_slash = false
HTTP inspector simplifies directory paths in URIs by eliminating extra traversals using ., .., and /.
For example I can take a simple URI such as
/very/easy/example
and complicate it like this:
/very/../very/././././easy//////detour/to/nowhere/../.././../example
which may be very difficult to match with a detection rule. simplify_path is on by default and you should not turn it off unless
you have no interest in URI paths.
backslash_to_slash is a tweak to path simplification for servers that allow directories to be separated by backslashes:
/this/is/the/normal/way/to/write/a/path
\this\is\the\other\way\to\write\a\path
backslash_to_slash is turned off by default. If you are protecting such a server then set backslash_to_slash = true and all the
backslashes will be replaced with slashes during normalization.
5.7.3 Detection rules
http_inspect parses HTTP messages into their components and makes them available to the detection engine through rule options.
Let’s start with an example:
alert tcp any any -> any any ( msg:"URI example"; flow:established,
to_server; http_uri; content:"chocolate"; sid:1; rev:1; )
This rule looks for chocolate in the URI portion of the request message. Specifically, the http_uri rule option is the normalized
URI with all the percent encodings removed. It will find chocolate in both:
GET /chocolate/cake HTTP/1.1
and
GET /%63%68$6F%63%6F%6C%61%74%65/%63%61%6B%65 HTTP/1.1
It is also possible to search the unnormalized URI
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alert tcp any any -> any any ( msg:"Raw URI example"; flow:established,
to_server; http_raw_uri; content:"chocolate"; sid:2; rev:1; )
will match the first message but not the second. If you want to detect someone who is trying to hide his request for chocolate
then
alert tcp any any -> any any ( msg:"Raw URI example"; flow:established,
to_server; http_raw_uri; content:"%63%68$6F%63%6F%6C%61%74%65";
sid:3; rev:1; )
will do the trick.
Let’s look at possible ways of writing a rule to match HTTP response messages with the Content-Language header set to "da"
(Danish). You could write:
alert tcp any any -> any any ( msg:"whole header search";
flow:established, to_client; http_header; content:
"Content-Language: da", nocase; sid:4; rev:1; )
This rule leaves much to be desired. Modern headers are often thousands of bytes and seem to get longer every year. Searching
all of the headers consumes a lot of resources. Furthermore this rule is easily evaded:
HTTP/1.1 ... Content-Language: da ...
the extra space before the "da" throws the rule off. Or how about:
HTTP/1.1 ... Content-Language: xx,da ...
By adding a made up second language the attacker has once again thwarted the match.
A better way to write this rule is:
alert tcp any any -> any any ( msg:"individual header search";
flow:established, to_client; http_header: field content-language;
content:"da", nocase; sid:4; rev:2; )
The field option improves performance by narrowing the search to the Content-Language field of the header. Because it uses the
header parsing abilities of http_inspect to find the field of interest it will not be thrown off by extra spaces or other languages in
the list.
In addition to the headers there are rule options for virtually every part of the HTTP message.
http_uri and http_raw_uri
These provide the URI of the request message. The raw form is exactly as it appeared in the message and the normalized form is
determined by the URI normalization options you selected. In addition to searching the entire URI there are six components that
can be searched individually:
alert tcp any any -> any any ( msg:"URI path"; flow:established,
to_server; http_uri: path; content:"chocolate"; sid:1; rev:2; )
By specifying "path" the search is limited to the path portion of the URI. Informally this is the part consisting of the directory
path and file name. Thus it will match:
GET /chocolate/cake HTTP/1.1
but not:
GET /book/recipes?chocolate+cake HTTP/1.1
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The question mark ends the path and begins the query portion of the URI. Informally the query is where parameter values are set
and often contains a search to be performed.
The six components are:
1. path: directory and file
2. query: user parameters
3. fragment: part of the file requested, normally found only inside a browser and not transmitted over the network
4. host: domain name of the server being addressed
5. port: TCP port number being addressed
6. scheme: normally "http" or "https" but others are possible such as "ftp"
Here is an example with all six:
GET https://www.samplehost.com:287/basic/example/of/path?with-query
#and-fragment HTTP/1.1\r\n
The URI is everything between the first space and the last space. "https" is the scheme, "www.samplehost.com" is the host, "287"
is the port, "/basic/example/of/path" is the path, "with-query" is the query, and "and-fragment" is the fragment.
Note: this section uses informal language to explain some things. Nothing here is intended to conflict with the technical language
of the HTTP RFCs and the implementation follows the RFCs.
http_header and http_raw_header
These cover all the header lines except the first one. You may specify an individual header by name using the field option as
shown in this earlier example:
alert tcp any any -> any any ( msg:"individual header search";
flow:established, to_client; http_header: field content-language;
content:"da", nocase; sid:4; rev:2; )
This rule searches the value of the Content-Language header. Header names are not case sensitive and may be written in the rule
in any mixture of upper and lower case.
With http_header the individual header value is normalized in a way that is appropriate for that header.
Specifying an individual header is not available for http_raw_header.
If you don’t specify a header you get all of the headers except for the cookie headers Cookie and Set-Cookie. http_raw_header
includes the unmodified header names and values as they appeared in the original message. http_header is the same except
percent encodings are removed and paths are simplified exactly as if the headers were a URI.
In most cases specifying individual headers creates a more efficient and accurate rule. It is recommended that new rules be
written using individual headers whenever possible.
http_trailer and http_raw_trailer
HTTP permits header lines to appear after a chunked body ends. Typically they contain information about the message content
that was not available when the headers were created. For convenience we call them trailers.
http_trailer and http_raw_trailer are identical to their header counterparts except they apply to these end headers. If you want a
rule to inspect both kinds of headers you need to write two rules, one using header and one using trailer.
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http_cookie and http_raw_cookie
These provide the value of the Cookie header for a request message and the Set-Cookie for a response message. If multiple
cookies are present they will be concatenated into a comma-separated list.
Normalization for http_cookie is the same URI-style normalization applied to http_header when no specific header is specified.
http_true_ip
This provides the original IP address of the client sending the request as it was stored by a proxy in the request message headers.
Specifically it is the last IP address listed in the X-Forwarded-For or True-Client-IP header. If both headers are present the former
is used.
http_client_body
This is the body of a request message such as POST or PUT. Normalization for http_client_body is the same URI-like normal-
ization applied to http_header when no specific header is specified.
http_raw_body
This is the body of a request or response message. It will be dechunked and unzipped if applicable but will not be normalized in
any other way. The difference between http_raw_body and packet data is a rule that uses packet data will search and may match
an HTTP header, but http_raw_body is limited to the message body. Thus the latter is more efficient and more accurate for most
uses.
http_method
The method field of a request message. Common values are "GET", "POST", "OPTIONS", "HEAD", "DELETE", "PUT",
"TRACE", and "CONNECT".
http_stat_code
The status code field of a response message. This is normally a 3-digit number between 100 and 599. In this example it is 200.
HTTP/1.1 200 OK
http_stat_msg
The reason phrase field of a response message. This is the human-readable text following the status code. "OK" in the previous
example.
http_version
The protocol version information that appears on the first line of an HTTP message. This is usually "HTTP/1.0" or "HTTP/1.1".
http_raw_request and http_raw_status
These are the unmodified first header line of the HTTP request and response messages respectively. These rule options are a
safety valve in case you need to do something you cannot otherwise do. In most cases it is better to use a rule option for a
specific part of the first header line. For a request message those are http_method, http_raw_uri, and http_version. For a response
message those are http_version, http_stat_code, and http_stat_msg.
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file_data and packet data
file_data contains the normalized message body. This is the normalization described above under gzip, normalize_utf, decom-
press_pdf, decompress_swf, and normalize_javascript.
The unnormalized message content is available in the packet data. If gzip is configured the packet data will be unzipped.
5.7.4 Timing issues and combining rule options
HTTP inspector is stateful. That means it is aware of a bigger picture than the packet in front of it. It knows what all the pieces of
a message are, the dividing lines between one message and the next, which request message triggered which response message,
pipelines, and how many messages have been sent over the current connection.
Some rules use a single rule option:
alert tcp any any -> any any ( msg:"URI example"; flow:established,
to_server; http_uri; content:"chocolate"; sid:1; rev:1; )
Whenever a new URI is available this rule will be evaluated. Nothing complicated about that, but suppose we use more than one
rule option:
alert tcp any any -> any any ( msg:"combined example"; flow:established,
to_server; http_uri; content:"chocolate"; file_data;
content:"sinister POST data"; sid:5; rev:1; )
This rule requires both the URI and the request message body. That sounds simple until one considers that the message body
may be millions of bytes long. The headers with the URI may be long gone by that time.
Is this rule going to work or do we need to do something different?
It is helpful to understand when things happen. All the message headers and the first few thousand bytes of the body go through
detection at the same time. Commonly this is about 16K bytes but there are several exceptions and there is no guaranteed
minimum amount.
That may be all you need. In many cases that will be the entire message. Or it may be more than your request_depth/response_depth.
Or this rule may simply not care what happens after that in a very long message body.
Beyond that the message body will continue to be subdivided into roughly 16K-byte sections and inspected. But the previous
rule will not be able to see the URI and hence will not work unless we rewrite it:
alert tcp any any -> any any ( msg:"URI with_body"; flow:established,
to_server; http_uri: with_body; content:"chocolate"; file_data;
content:"sinister POST data"; sid:5; rev:2; )
The with_body option to http_uri causes the URI to be made available with every body section, not just the first one. These extra
inspections have a performance cost which is why they are not done automatically. with_body is an option to be used when you
actually need it.
The with_trailer option is analogous and causes an earlier message element to be made available at the end of the message when
the trailers following a chunked body arrive.
alert tcp any any -> any any ( msg:"double content-language";
flow:established, to_client; http_header: with_trailer, field
content-language; content:"da", nocase; http_trailer: field
content-language; content:"en", nocase; sid:6; rev:1; )
This rule will alert if the Content-Language changes from Danish in the headers to English in the trailers. The with_trailer option
is essential to make this rule work.
It is also possible to write rules that examine both the client request and the server response to it.
Snort 3 User Manual 52 / 284
alert tcp any any -> any any ( msg:"request and response example";
flow:established, to_client; http_uri: with_body; content:"chocolate";
file_data; content:"white chocolate"; sid:7; rev:1; )
This rule looks for white chocolate in a response message body where the URI of the request contained chocolate. Note that this
is a "to_client" rule that will alert on and potentially block a server response containing white chocolate, but only if the client
URI requested chocolate. If the rule were rewritten "to_server" it would be nonsense and not work. Snort cannot block a client
request based on what the server response will be because that has not happened yet.
Another point is "with_body" for http_uri. This ensures the rule works on the entire response body. If we were looking for white
chocolate in the response headers this would not be necessary.
Response messages do not have a URI so there was only one thing http_uri could have meant in the previous rule. It had to be
referring to the request message. Sometimes that is not so clear.
alert tcp any any -> any any ( msg:"header ambiguity example 1";
flow:established, to_client; http_header: with_body; content:
"chocolate"; file_data; content:"white chocolate"; sid:8; rev:1; )
alert tcp any any -> any any ( msg:"header ambiguity example 2";
flow:established, to_client; http_header: with_body, request; content:
"chocolate"; file_data; content:"white chocolate"; sid:8; rev:2; )
Our search for chocolate has moved from the URI to the message headers. Both the request and response messages have
headers—which one are we asking about? Ambiguity is always resolved in favor of looking in the current message which is the
response. The first rule is looking for a server response containing chocolate in the headers and white chocolate in the body.
The second rule uses the "request" option to explicitly say that the http_header to be searched is the request header.
Let’s put all of this together. There are six opportunities to do detection:
1. When the first part of the request message body arrives. The request line, all of the headers, and the first part of the body
all go through detection at the same time. Of course most requests don’t have a body. In that case the request line and the
headers are the whole message and get done at the same time.
2. When subsequent sections of the request message body arrive. If you want to combine this with something from the request
line or headers you must use the with_body option.
3. When the request trailers arrive. If you want to combine this with something from the request line or headers you must use
the with_trailer option.
4. When the first part of the response message body arrives. The status line, all of the headers, and the first part of the body
all go through detection at the same time. These may be combined with elements from the request line, request headers,
or request trailers. Where ambiguity arises use the request option.
5. When subsequent sections of the response message body arrive. These may be combined with the status line, response
headers, request line, request headers, or request trailers as described above.
6. When the response trailers arrive. Again these may be combined as described above.
Message body data can only go through detection at the time it is received. Headers may be combined with later items but the
body cannot.
5.8 Performance Monitor
The new and improved performance monitor! Is your sensor being bogged down by too many flows? perf_monitor! Why are
certain TCP segments being dropped without hitting a rule? perf_monitor! Why is a sensor leaking water? Not perf_monitor,
check with stream. . .
Snort 3 User Manual 53 / 284
5.8.1 Overview
The Snort performance monitor is the built-in utility for monitoring system and traffic statistics. All statistics are separated by
processing thread. perf_monitor supports several trackers for monitoring such data:
5.8.2 Base Tracker
The base tracker is used to gather running statistics about Snort and its running modules. All Snort modules gather, at the very
least, counters for the number of packets reaching it. Most supplement these counts with those for domain specific functions,
such as http_inspect’s number of GET requests seen.
Statistics are gathered live and can be reported at regular intervals. The stats reported correspond only to the interval in question
and are reset at the beginning of each interval.
These are the same counts displayed when Snort shuts down, only sorted amongst the discrete intervals in which they occurred.
Base differs from prior implementations in Snort in that all stats gathered are only raw counts, allowing the data to be evaluated
as needed. Additionally, base is entirely pluggable. Data from new Snort plugins can be added to the existing stats either
automatically or, if specified, by name and function.
All plugins and counters can be enabled or disabled individually, allowing for only the data that is actually desired instead of
overly verbose performance logs.
To enable everything:
perf_monitor = { modules = {} }
To enable everything within a module:
perf_monitor =
{
modules =
{
{
name = ’stream_tcp’,
pegs = [[ ]]
},
}
}
To enable specific counts within modules:
perf_monitor =
{
modules =
{
{
name = ’stream_tcp’,
pegs = [[ overlaps gaps ]]
},
}
Note: Event stats from prior Snorts are now located within base statistics.
5.8.3 Flow Tracker
Flow tracks statistics regarding traffic and L3/L4 protocol distributions. This data can be used to build a profile of traffic for
inspector tuning and for identifying where Snort may be stressed.
To enable:
perf_monitor = { flow = true }
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5.8.4 FlowIP Tracker
FlowIP provides statistics for individual hosts within a network. This data can be used for identifying communication habits,
such as generating large or small amounts of data, opening a small or large number of sessions, and tendency to send smaller or
larger IP packets.
To enable:
perf_monitor = { flow_ip = true }
5.8.5 CPU Tracker
This tracker monitors the CPU and wall time spent by a given processing thread.
To enable:
perf_monitor = { cpu = true }
5.8.6 Formatters
Performance monitor allows statistics to be output in a few formats. Along with human readable text (as seen at shutdown) and
csv formats, a Flatbuffers binary format is also available if Flatbuffers is present at build. A utility for accessing the statistics
generated in this format has been included for convenience (see fbstreamer in tools). This tool generates a YAML array of records
found, allowing the data to be read by humans or passed into other analysis tools. For information on working directly with the
Flatbuffers file format used by Performance monitor, see the developer notes for Performance monitor or the code provided for
fbstreamer.
5.9 POP and IMAP
POP inspector is a service inspector for POP3 protocol and IMAP inspector is for IMAP4 protocol.
5.9.1 Overview
POP and IMAP inspectors examine data traffic and find POP and IMAP commands and responses. The inspectors also identify
the command, header, body sections and extract the MIME attachments and decode it appropriately. The pop and imap also
identify and whitelist the pop and imap traffic.
5.9.2 Configuration
POP inspector and IMAP inspector offer same set of configuration options for MIME decoding depth:
b64_decode_depth
This config option is used to turn off/on or set the base64 decoding depth used to decode the base64 encoded MIME attachments.
The value ranges from -1 to 65535. A value of -1 turns off the base64 decoding of MIME attachments. The value of 0 sets the
decoding of base64 encoded MIME attachments to unlimited. A value other than 0 or -1 restricts the decoding of base64 MIME
attachments, and applies per attachment. The default value is 1460.
qp_decode_depth
This config option is used to turn off/on or set the Quoted-Printable decoding depth used to decode the Quoted-Printable(QP)
encoded MIME attachments. The value ranges from -1 to 65535. A value of -1 turns off the QP decoding of MIME attachments.
The value of 0 sets the decoding of QP encoded MIME attachments to unlimited. A value other than 0 or -1 restricts the decoding
of QP MIME attachments, and applies per attachment.
Snort 3 User Manual 55 / 284
bitenc_decode_depth
This config option is used to turn off/on or set the non-encoded MIME extraction depth used to extract the non-encoded MIME
attachments. The value ranges from -1 to 65535. A value of -1 turns off the extraction of these MIME attachments. The value of
0 sets the extraction of these MIME attachments to unlimited. A value other than 0 or -1 restricts the extraction of these MIME
attachments, and applies per attachment.
uu_decode_depth
This config option is used to turn off/on or set the Unix-to-Unix decoding depth used to decode the Unix-to-Unix(UU) encoded
attachments. The value ranges from -1 to 65535. A value of -1 turns off the UU decoding of POP attachments. The value of 0
sets the decoding of UU encoded POP attachments to unlimited. A value other than 0 or -1 restricts the decoding of UU POP
attachments, and applies per attachment.
Examples
stream = { }
stream_tcp = { }
stream_ip = { }
binder =
{
{
{
when = { proto = ’tcp’, ports = ’110’, },
use = { type = ’pop’, },
},
{
when = { proto = ’tcp’, ports = ’143’, },
use = { type = ’imap’, },
},
},
}
imap =
{
qp_decode_depth = 15,
}
pop =
{
qp_decode_depth = 0,
b64_decode_depth = 10,
}
5.10 Port Scan
A module to detect port scanning
Snort 3 User Manual 56 / 284
5.10.1 Overview
This module is designed to detect the first phase in a network attack: Reconnaissance. In the Reconnaissance phase, an attacker
determines what types of network protocols or services a host supports. This is the traditional place where a portscan takes place.
This phase assumes the attacking host has no prior knowledge of what protocols or services are supported by the target, otherwise
this phase would not be necessary.
As the attacker has no beforehand knowledge of its intended target, most queries sent by the attacker will be negative (meaning
that the services are closed). In the nature of legitimate network communications, negative responses from hosts are rare, and
rarer still are multiple negative responses within a given amount of time. Our primary objective in detecting portscans is to detect
and track these negative responses.
One of the most common portscanning tools in use today is Nmap. Nmap encompasses many, if not all, of the current portscan-
ning techniques. Portscan was designed to be able to detect the different types of scans Nmap can produce.
The following are a list of the types of Nmap scans Portscan will currently alert for.
• TCP Portscan
• UDP Portscan
• IP Portscan
These alerts are for one to one portscans, which are the traditional types of scans; one host scans multiple ports on another host.
Most of the port queries will be negative, since most hosts have relatively few services available.
• TCP Decoy Portscan
• UDP Decoy Portscan
• IP Decoy Portscan
Decoy portscans are much like regular, only the attacker has spoofed source address inter-mixed with the real scanning address.
This tactic helps hide the true identity of the attacker.
• TCP Distributed Portscan
• UDP Distributed Portscan
• IP Distributed Portscan
These are many to one portscans. Distributed portscans occur when multiple hosts query one host for open services. This is used
to evade an IDS and obfuscate command and control hosts.
Note
Negative queries will be distributed among scanning hosts, so we track this type of scan through the scanned host.
• TCP Portsweep
• UDP Portsweep
• IP Portsweep
• ICMP Portsweep
These alerts are for one to many portsweeps. One host scans a single port on multiple hosts. This usually occurs when a new
exploit comes out and the attacker is looking for a specific service.
Snort 3 User Manual 57 / 284
Note
The characteristics of a portsweep scan may not result in many negative responses. For example, if an attacker portsweeps a
web farm for port 80, we will most likely not see many negative responses.
• TCP Filtered Portscan
• UDP Filtered Portscan
• IP Filtered Portscan
• TCP Filtered Decoy Portscan
• UDP Filtered Decoy Portscan
• IP Filtered Decoy Portscan
• TCP Filtered Portsweep
• UDP Filtered Portsweep
• IP Filtered Portsweep
• ICMP Filtered Portsweep
• TCP Filtered Distributed Portscan
• UDP Filtered Distributed Portscan
• IP Filtered Distributed Portscan
"Filtered" alerts indicate that there were no network errors (ICMP unreachables or TCP RSTs) or responses on closed ports have
been suppressed. It’s also a good indicator on whether the alert is just a very active legitimate host. Active hosts, such as NATs,
can trigger these alerts because they can send out many connection attempts within a very small amount of time. A filtered alert
may go off before responses from the remote hosts are received.
Portscan only generates one alert for each host pair in question during the time window. On TCP scan alerts, Portscan will also
display any open ports that were scanned. On TCP sweep alerts however, Portscan will only track open ports after the alert has
been triggered. Open port events are not individual alerts, but tags based off the original scan alert.
5.10.2 Scan levels
There are 3 default scan levels that can be set.
1) default_hi_port_scan
2) default_med_port_scan
3) default_low_port_scan
Each of these default levels have separate options that can be edited to alter the scan sensitivity levels (scans, rejects, nets or
ports)
Example:
port_scan = default_low_port_scan
port_scan.tcp_decoy.ports = 1
port_scan.tcp_decoy.scans = 1
port_scan.tcp_decoy.rejects = 1
port_scan.tcp_ports.nets = 1
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The example above would change each of the individual settings to 1.
NOTE:The default levels for scans, rejects, nets and ports can be seen in the snort_defaults.lua file.
The counts can be seen in the alert outputs (-Acmg shown below):
50 72 69 6F 72 69 74 79 20 43 6F 75 6E 74 3A 20 Priority Count:
30 0A 43 6F 6E 6E 65 63 74 69 6F 6E 20 43 6F 75 0.Connec tion Cou
6E 74 3A 20 34 35 0A 49 50 20 43 6F 75 6E 74 3A nt: 45.I P Count:
20 31 0A 53 63 61 6E 6E 65 72 20 49 50 20 52 61 1.Scann er IP Ra
6E 67 65 3A 20 31 2E 32 2E 33 2E 34 3A 31 2E 32 nge: 1.2 .3.4:1.2
2E 33 2E 34 0A 50 6F 72 74 2F 50 72 6F 74 6F 20 .3.4.Por t/Proto
43 6F 75 6E 74 3A 20 33 37 0A 50 6F 72 74 2F 50 Count: 3 7.Port/P
72 6F 74 6F 20 52 61 6E 67 65 3A 20 31 3A 39 0A roto Ran ge: 1:9.
"Low" alerts are only generated on error packets sent from the target host, and because of the nature of error responses, this
setting should see very few false positives. However, this setting will never trigger a Filtered Scan alert because of a lack of error
responses. This setting is based on a static time window of 60 seconds, after which this window is reset.
"Medium" alerts track Connection Counts, and so will generate Filtered Scan alerts. This setting may false positive on active
hosts (NATs, proxies, DNS caches, etc), so the user may need to deploy the use of Ignore directives to properly tune this directive.
"High" alerts continuously track hosts on a network using a time window to evaluate portscan statistics for that host. A "High"
setting will catch some slow scans because of the continuous monitoring, but is very sensitive to active hosts. This most definitely
will require the user to tune Portscan.
5.10.3 Tuning Portscan
The most important aspect in detecting portscans is tuning the detection engine for your network(s). Here are some tuning tips:
Use the watch_ip, ignore_scanners, and ignore_scanned options. It’s important to correctly set these options. The watch_ip
option is easy to understand. The analyst should set this option to the list of CIDR blocks and IPs that they want to watch. If no
watch_ip is defined, Portscan will watch all network traffic. The ignore_scanners and ignore_scanned options come into play in
weeding out legitimate hosts that are very active on your network. Some of the most common examples are NAT IPs, DNS cache
servers, syslog servers, and nfs servers. Portscan may not generate false positives for these types of hosts, but be aware when first
tuning Portscan for these IPs. Depending on the type of alert that the host generates, the analyst will know which to ignore it as.
If the host is generating portsweep events, then add it to the ignore_scanners option. If the host is generating portscan alerts (and
is the host that is being scanned), add it to the ignore_scanned option.
Filtered scan alerts are much more prone to false positives. When determining false positives, the alert type is very important.
Most of the false positives that Portscan may generate are of the filtered scan alert type. So be much more suspicious of filtered
portscans. Many times this just indicates that a host was very active during the time period in question. If the host continually
generates these types of alerts, add it to the ignore_scanners list or use a lower sensitivity level.
Make use of the Priority Count, Connection Count, IP Count, Port Count, IP range, and Port range to determine false positives.
The portscan alert details are vital in determining the scope of a portscan and also the confidence of the portscan. In the future,
we hope to automate much of this analysis in assigning a scope level and confidence level, but for now the user must manually do
this. The easiest way to determine false positives is through simple ratio estimations. The following is a list of ratios to estimate
and the associated values that indicate a legitimate scan and not a false positive.
Connection Count / IP Count: This ratio indicates an estimated average of connections per IP. For portscans, this ratio should be
high, the higher the better. For portsweeps, this ratio should be low.
Port Count / IP Count: This ratio indicates an estimated average of ports connected to per IP. For portscans, this ratio should
be high and indicates that the scanned host’s ports were connected to by fewer IPs. For portsweeps, this ratio should be low,
indicating that the scanning host connected to few ports but on many hosts.
Connection Count / Port Count: This ratio indicates an estimated average of connections per port. For portscans, this ratio should
be low. This indicates that each connection was to a different port. For portsweeps, this ratio should be high. This indicates that
there were many connections to the same port.
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The reason that Priority Count is not included, is because the priority count is included in the connection count and the above
comparisons take that into consideration. The Priority Count play an important role in tuning because the higher the priority
count the more likely it is a real portscan or portsweep (unless the host is firewalled).
If all else fails, lower the sensitivity level. If none of these other tuning techniques work or the analyst doesn’t have the time
for tuning, lower the sensitivity level. You get the best protection the higher the sensitivity level, but it’s also important that the
portscan detection engine generates alerts that the analyst will find informative. The low sensitivity level only generates alerts
based on error responses. These responses indicate a portscan and the alerts generated by the low sensitivity level are highly
accurate and require the least tuning. The low sensitivity level does not catch filtered scans, since these are more prone to false
positives.
5.11 Sensitive Data Filtering
The sd_pattern IPS option provides detection and filtering of Personally Identifiable Information (PII). This information
includes credit card numbers, U.S. Social Security numbers, and email addresses. A rich regular expression syntax is available
for defining your own PII.
5.11.1 Hyperscan
The sd_pattern rule option is powered by the open source Hyperscan library from Intel. It provides a regex grammar which
is mostly PCRE compatible. To learn more about Hyperscan see http://01org.github.io/hyperscan/dev-reference/
5.11.2 Syntax
Snort provides sd_pattern as IPS rule option with no additional inspector overhead. The Rule option takes the following
syntax.
sd_pattern: "<pattern>"[, threshold <count>];
Pattern
Pattern is the most important and is the only required parameter to sd_pattern. It supports 3 built in patterns which are
configured by name: "credit_card", "us_social" and "us_social_nodashes", as well as user defined regular expressions of the
Hyperscan dialect (see http://01org.github.io/hyperscan/dev-reference/compilation.html#pattern-support).
sd_pattern:"credit_card";
When configured, Snort will replace the pattern credit_card with the built in pattern. In addition to pattern matching, Snort will
validate that the matched digits will pass the Luhn-check algorithm. Currently the only pattern that performs extra verification.
sd_pattern:"us_social";
sd_pattern:"us_social_nodashes";
These special patterns will also be replaced with a built in pattern. Naturally, "us_social" is a pattern of 9 digits separated by -’s
in the canonical form.
sd_pattern:"\b\w+@ourdomain\.com\b"
This is a user defined pattern which matches what is most likely email addresses for the site "ourdomain.com". The pattern is
a PCRE compatible regex, \b matches a word boundary (whitespace, end of line, non-word characters) and \w+ matches one or
more word characters. \. matches a literal ..
The above pattern would match "a@ourdomain.com", "aa@ourdomain.com" but would not match 1@ourdomain.com ab12@
ourdomain.com or @ourdomain.com.
Note: This is just an example, this pattern is not suitable to detect many correctly formatted emails.
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Threshold
Threshold is an optional parameter allowing you to change built in default value (default value is 1). The following two instances
are identical. The first will assume the default value of 1the second declaration explicitly sets the threshold to 1.
sd_pattern:"This rule requires 1 match";
sd_pattern:"This rule requires 1 match", threshold 1;
That’s pretty easy, but here is one more example anyway.
sd_pattern:"This is a string literal", threshold 300;
This example requires 300 matches of the pattern "This is a string literal" to qualify as a positive match. That is, if the string only
occurred 299 times in a packet, you will not see an event.
Obfuscating Credit Cards and Social Security Numbers
Snort provides discreet logging for the built in patterns "credit_card", "us_social" and "us_social_nodashes". Enabling output.
obfuscate_pii makes Snort obfuscate the suspect packet payload which was matched by the patterns. This configuration is
disabled by default.
output =
{
obfuscate_pii = true
}
5.11.3 Example
A complete Snort IPS rule
alert tcp ( sid:1; msg:"Credit Card"; sd_pattern:"credit_card"; )
Logged output when running Snort in "cmg" alert format.
02/25-21:19:05.125553 [**] [1:1:0] "Credit Card" [**] [Priority: 0] {TCP} ←-
10.1.2.3:48620 -> 10.9.8.7:8
02:01:02:03:04:05 -> 02:09:08:07:06:05 type:0x800 len:0x46
10.1.2.3:48620 -> 10.9.8.7:8 TCP TTL:64 TOS:0x0 ID:14 IpLen:20 DgmLen:56
***A**** Seq: 0xB2 Ack: 0x2 Win: 0x2000 TcpLen: 20
---raw[16]----------------------------------
58 58 58 58 58 58 58 58 58 58 58 58 39 32 39 34 XXXXXXXXXXXX9294
-----------------------------------------
5.11.4 Caveats
1. Snort currently requires setting the fast pattern engine to use "hyperscan" in order for sd_pattern ips option to function
correctly.
search_engine = { search_method = ’hyperscan’ }
2. Log obfuscation is only applicable to CMG and Unified2 logging formats.
3. Log obfuscation doesn’t support user defined PII patterns. It is currently only supported for the built in patterns for Credit
Cards and US Social Security numbers.
4. Log obfuscation doesn’t work with stream rebuilt packet payloads. (This is a known bug).
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5.12 SMTP
SMTP inspector is a service inspector for SMTP protocol.
5.12.1 Overview
The SMTP inspector examines SMTP connections looking for commands and responses. It also identifies the command, header
and body sections, TLS data and extracts the MIME attachments. This inspector also identifies and whitelists the SMTP traffic.
SMTP inspector logs the filename, email addresses, attachment names when configured.
5.12.2 Configuration
SMTP command lines can be normalized to remove extraneous spaces. TLS-encrypted traffic can be ignored, which improves
performance. In addition, plain-text mail data can be ignored for an additional performance boost.
The configuration options are described below:
normalize and normalize_cmds
Normalization checks for more than one space character after a command. Space characters are defined as space (ASCII 0x20)
or tab (ASCII 0x09). "normalize" provides options all|none|cmds, all checks all commands, none turns off normalization for all
commands. cmds just checks commands listed with the "normalize_cmds" parameter. For example:
smtp = { normalize = ’cmds’, normalize_cmds = ’RCPT VRFY EXPN’ }
ignore_data
Set it to true to ignore data section of mail (except for mail headers) when processing rules.
ignore_tls_data
Set it to true to ignore TLS-encrypted data when processing rules.
max_command_line_len
Alert if an SMTP command line is longer than this value. Absence of this option or a "0" means never alert on command line
length. RFC 2821 recommends 512 as a maximum command line length.
max_header_line_len
Alert if an SMTP DATA header line is longer than this value. Absence of this option or a "0" means never alert on data header
line length. RFC 2821 recommends 1024 as a maximum data header line length.
max_response_line_len
Alert if an SMTP response line is longer than this value. Absence of this option or a "0" means never alert on response line
length. RFC 2821 recommends 512 as a maximum response line length.
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alt_max_command_line_len
Overrides max_command_line_len for specific commands For example:
alt_max_command_line_len =
{
{
command = ’MAIL’,
length = 260,
},
{
command = ’RCPT’,
length = 300,
},
}
invalid_cmds
Alert if this command is sent from client side.
valid_cmds
List of valid commands. We do not alert on commands in this list.
DEFAULT empty list, but SMTP inspector has this list hard-coded: [[ ATRN AUTH BDAT DATA DEBUG EHLO EMAL ESAM
ESND ESOM ETRN EVFY EXPN HELO HELP IDENT MAIL NOOP ONEX QUEU QUIT RCPT RSET SAML SEND SIZE
STARTTLS SOML TICK TIME TURN TURNME VERB VRFY X-EXPS X-LINK2STATE XADR XAUTH XCIR XEXCH50
XGEN XLICENSE XQUE XSTA XTRN XUSR ]]
data_cmds
List of commands that initiate sending of data with an end of data delimiter the same as that of the DATA command per RFC
5321 - "<CRLF>.<CRLF>".
binary_data_cmds
List of commands that initiate sending of data and use a length value after the command to indicate the amount of data to be sent,
similar to that of the BDAT command per RFC 3030.
auth_cmds
List of commands that initiate an authentication exchange between client and server.
xlink2state
Enable/disable xlink2state alert, options are {disable | alert | drop}. See CVE-2005-0560 for a description of the vulnerability.
b64_decode_depth
This config option is used to turn off/on or set the base64 decoding depth used to decode the base64 encoded MIME attachments.
The value ranges from -1 to 65535. A value of -1 turns off the base64 decoding of MIME attachments. The value of 0 sets the
decoding of base64 encoded MIME attachments to unlimited. A value other than 0 or -1 restricts the decoding of base64 MIME
attachments, and applies per attachment.
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qp_decode_depth
This config option is used to turn off/on or set the Quoted-Printable decoding depth used to decode the Quoted-Printable(QP)
encoded MIME attachments. The value ranges from -1 to 65535. A value of -1 turns off the QP decoding of MIME attachments.
The value of 0 sets the decoding of QP encoded MIME attachments to unlimited. A value other than 0 or -1 restricts the decoding
of QP MIME attachments, and applies per attachment.
bitenc_decode_depth * default to 25
This config option is used to turn off/on or set the non-encoded MIME extraction depth used to extract the non-encoded MIME
attachments. The value ranges from -1 to 65535. A value of -1 turns off the extraction of these MIME attachments. The value of
0 sets the extraction of these MIME attachments to unlimited. A value other than 0 or -1 restricts the extraction of these MIME
attachments, and applies per attachment.
uu_decode_depth
This config option is used to turn off/on or set the Unix-to-Unix decoding depth used to decode the Unix-to-Unix(UU) encoded
attachments. The value ranges from -1 to 65535. A value of -1 turns off the UU decoding of SMTP attachments. The value of 0
sets the decoding of UU encoded SMTP attachments to unlimited. A value other than 0 or -1 restricts the decoding of UU SMTP
attachments, and applies per attachment.
Log Options
Following log options allow SMTP inspector to log email addresses and filenames. Please note, this is logged only with the
unified2 output and is not logged with the console output (-A cmg). u2spewfoo can be used to read this data from the unified2.
log_mailfrom
This option enables SMTP inspector to parse and log the sender’s email address extracted from the "MAIL FROM" command
along with all the generated events for that session. The maximum number of bytes logged for this option is 1024.
log_rcptto
This option enables SMTP inspector to parse and log the recipient email addresses extracted from the "RCPT TO" command
along with all the generated events for that session. Multiple recipients are appended with commas. The maximum number of
bytes logged for this option is 1024.
log_filename
This option enables SMTP inspector to parse and log the MIME attachment filenames extracted from the Content-Disposition
header within the MIME body along with all the generated events for that session. Multiple filenames are appended with commas.
The maximum number of bytes logged for this option is 1024.
log_email_hdrs
This option enables SMTP inspector to parse and log the SMTP email headers extracted from SMTP data along with all generated
events for that session. The number of bytes extracted and logged depends upon the email_hdrs_log_depth.
email_hdrs_log_depth
This option specifies the depth for logging email headers. The allowed range for this option is 0 - 20480. A value of 0 will
disable email headers logging. The default value for this option is 1464.
5.12.3 Example
smtp =
{
normalize = ’cmds’,
normalize_cmds = ’EXPN VRFY RCPT’,
b64_decode_depth = 0,
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qp_decode_depth = 0,
bitenc_decode_depth = 0,
uu_decode_depth = 0,
log_mailfrom = true,
log_rcptto = true,
log_filename = true,
log_email_hdrs = true,
max_command_line_len = 512,
max_header_line_len = 1000,
max_response_line_len = 512,
max_auth_command_line_len = 50,
xlink2state = ’alert’,
alt_max_command_line_len =
{
{
command = ’MAIL’,
length = 260,
},
{
command = ’RCPT’,
length = 300,
},
{
command = ’HELP’,
length = 500,
},
{
command = ’HELO’,
length = 500,
},
{
command = ’ETRN’,
length = 500,
},
{
command = ’EXPN’,
length = 255,
},
{
command = ’VRFY’,
length = 255,
},
},
}
5.13 Wizard
Using the wizard enables port-independent configuration and the detection of malware command and control channels. If the
wizard is bound to a session, it peeks at the initial payload to determine the service. For example, GET would indicate HTTP
and HELO would indicate SMTP. Upon finding a match, the service bindings are reevaluated so the session can be handed off to
the appropriate inspector. The wizard is still under development; if you find you need to tweak the defaults please let us know.
Additional Details:
• If the wizard and one or more service inspectors are configured w/o explicitly configuring the binder, default bindings will be
generated which should work for most common cases.
Snort 3 User Manual 65 / 284
• Also note that while Snort 2 bindings can only be configured in the default policy, each Snort 3 policy can contain a binder
leading to an arbitrary hierarchy.
• The entire configuration can be reloaded and hot-swapped during run-time via signal or command in both Snort 2 and Snort
3. Ultimately, Snort 3 will support commands to update the binder on the fly, thus enabling incremental reloads of individual
inspectors.
• Both Snort 2 and Snort 3 support server specific configurations via a hosts table (XML in Snort 2 and Lua in Snort 3). The table
allows you to map network, protocol, and port to a service and policy. This table can be reloaded and hot-swapped separately
from the config file.
• You can find the specifics on the binder, wizard, and hosts tables in the manual or command line like this: snort --help-module
binder, etc.
6 Basic Modules
Internal modules which are not plugins are termed "basic". These include configuration for core processing.
6.1 active
What: configure responses
Type: basic
Usage: global
Configuration:
• int active.attempts = 0: number of TCP packets sent per response (with varying sequence numbers) { 0:20 }
• string active.device: use ip for network layer responses or eth0 etc for link layer
• string active.dst_mac: use format 01:23:45:67:89:ab
• int active.max_responses = 0: maximum number of responses { 0: }
• int active.min_interval = 255: minimum number of seconds between responses { 1: }
6.2 alerts
What: configure alerts
Type: basic
Usage: global
Configuration:
• bool alerts.alert_with_interface_name = false: include interface in alert info (fast, full, or syslog only)
• bool alerts.default_rule_state = true: enable or disable ips rules
• int alerts.detection_filter_memcap = 1048576: set available bytes of memory for detection_filters { 0: }
• int alerts.event_filter_memcap = 1048576: set available bytes of memory for event_filters { 0: }
• bool alerts.log_references = false: include rule references in alert info (full only)
• string alerts.order = pass drop alert log: change the order of rule action application
• int alerts.rate_filter_memcap = 1048576: set available bytes of memory for rate_filters { 0: }
• string alerts.reference_net: set the CIDR for homenet (for use with -l or -B, does NOT change $HOME_NET in IDS mode)
• bool alerts.stateful = false: don’t alert w/o established session (note: rule action still taken)
• string alerts.tunnel_verdicts: let DAQ handle non-allow verdicts for gtp|teredo|6in4|4in6|4in4|6in6|gre|mpls traffic
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6.3 attribute_table
What: configure hosts loading
Type: basic
Usage: global
Configuration:
• int attribute_table.max_hosts = 1024: maximum number of hosts in attribute table { 32:207551 }
• int attribute_table.max_services_per_host = 8: maximum number of services per host entry in attribute table { 1:65535 }
• int attribute_table.max_metadata_services = 8: maximum number of services in rule metadata { 1:256 }
6.4 classifications
What: define rule categories with priority
Type: basic
Usage: global
Configuration:
• string classifications[].name: name used with classtype rule option
• int classifications[].priority = 1: default priority for class { 0: }
• string classifications[].text: description of class
6.5 daq
What: configure packet acquisition interface
Type: basic
Usage: global
Configuration:
• string daq.module_dirs[].str: string parameter
• string daq.input_spec: input specification
• string daq.module: DAQ module to use
• string daq.variables[].str: string parameter
• int daq.instances[].id: instance ID (required) { 0: }
• string daq.instances[].input_spec: input specification
• string daq.instances[].variables[].str: string parameter
• int daq.snaplen: set snap length (same as -s) { 0:65535 }
• bool daq.no_promisc = false: whether to put DAQ device into promiscuous mode
Peg counts:
•daq.pcaps: total files and interfaces processed (sum)
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•daq.received: total packets received from DAQ (sum)
•daq.analyzed: total packets analyzed from DAQ (sum)
•daq.dropped: packets dropped (sum)
•daq.filtered: packets filtered out (sum)
•daq.outstanding: packets unprocessed (sum)
•daq.injected: active responses or replacements (sum)
•daq.allow: total allow verdicts (sum)
•daq.block: total block verdicts (sum)
•daq.replace: total replace verdicts (sum)
•daq.whitelist: total whitelist verdicts (sum)
•daq.blacklist: total blacklist verdicts (sum)
•daq.ignore: total ignore verdicts (sum)
•daq.retry: total retry verdicts (sum)
•daq.internal_blacklist: packets blacklisted internally due to lack of DAQ support (sum)
•daq.internal_whitelist: packets whitelisted internally due to lack of DAQ support (sum)
•daq.skipped: packets skipped at startup (sum)
•daq.idle: attempts to acquire from DAQ without available packets (sum)
•daq.rx_bytes: total bytes received (sum)
6.6 decode
What: general decoder rules
Type: basic
Usage: context
Rules:
•116:450 (decode) bad IP protocol
•116:293 (decode) two or more IP (v4 and/or v6) encapsulation layers present
•116:459 (decode) fragment with zero length
•116:150 (decode) loopback IP
•116:151 (decode) same src/dst IP
•116:449 (decode) unassigned/reserved IP protocol
•116:472 (decode) too many protocols present
•116:473 (decode) ether type out of range
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6.7 detection
What: configure general IPS rule processing parameters
Type: basic
Usage: global
Configuration:
• int detection.asn1 = 256: maximum decode nodes { 1: }
• int detection.offload_limit = 99999: minimum sizeof PDU to offload fast pattern search (defaults to disabled) { 0: }
• int detection.offload_threads = 0: maximum number of simultaneous offloads (defaults to disabled) { 0: }
• bool detection.pcre_enable = true: disable pcre pattern matching
• int detection.pcre_match_limit = 1500: limit pcre backtracking, -1 = max, 0 = off { -1:1000000 }
• int detection.pcre_match_limit_recursion = 1500: limit pcre stack consumption, -1 = max, 0 = off { -1:10000 }
• int detection.trace: mask for enabling debug traces in module
Peg counts:
•detection.analyzed: packets sent to detection (sum)
•detection.hard_evals: non-fast pattern rule evaluations (sum)
•detection.raw_searches: fast pattern searches in raw packet data (sum)
•detection.cooked_searches: fast pattern searches in cooked packet data (sum)
•detection.pkt_searches: fast pattern searches in packet data (sum)
•detection.alt_searches: alt fast pattern searches in packet data (sum)
•detection.key_searches: fast pattern searches in key buffer (sum)
•detection.header_searches: fast pattern searches in header buffer (sum)
•detection.body_searches: fast pattern searches in body buffer (sum)
•detection.file_searches: fast pattern searches in file buffer (sum)
•detection.offloads: fast pattern searches that were offloaded (sum)
•detection.alerts: alerts not including IP reputation (sum)
•detection.total_alerts: alerts including IP reputation (sum)
•detection.logged: logged packets (sum)
•detection.passed: passed packets (sum)
•detection.match_limit: fast pattern matches not processed (sum)
•detection.queue_limit: events not queued because queue full (sum)
•detection.log_limit: events queued but not logged (sum)
•detection.event_limit: events filtered (sum)
•detection.alert_limit: events previously triggered on same PDU (sum)
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6.8 event_filter
What: configure thresholding of events
Type: basic
Usage: context
Configuration:
• int event_filter[].gid = 1: rule generator ID { 0: }
• int event_filter[].sid = 1: rule signature ID { 0: }
• enum event_filter[].type: 1st count events | every count events | once after count events { limit | threshold | both }
• enum event_filter[].track: filter only matching source or destination addresses { by_src | by_dst }
• int event_filter[].count = 0: number of events in interval before tripping; -1 to disable { -1: }
• int event_filter[].seconds = 0: count interval { 0: }
• string event_filter[].ip: restrict filter to these addresses according to track
6.9 event_queue
What: configure event queue parameters
Type: basic
Usage: context
Configuration:
• int event_queue.max_queue = 8: maximum events to queue { 1: }
• int event_queue.log = 3: maximum events to log { 1: }
• enum event_queue.order_events = content_length: criteria for ordering incoming events { priority|content_length }
• bool event_queue.process_all_events = false: process just first action group or all action groups
6.10 high_availability
What: implement flow tracking high availability
Type: basic
Usage: global
Configuration:
• bool high_availability.enable = false: enable high availability
• bool high_availability.daq_channel = false: enable use of daq data plane channel
• bit_list high_availability.ports: side channel message port list { 65535 }
• real high_availability.min_age = 1.0: minimum session life before HA updates { 0.0:100.0 }
• real high_availability.min_sync = 1.0: minimum interval between HA updates { 0.0:100.0 }
Peg counts:
•high_availability.packets: total packets (sum)
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6.11 host_cache
What: configure hosts
Type: basic
Usage: global
Configuration:
• int host_cache[].size: size of host cache
Peg counts:
•host_cache.lru_cache_adds: lru cache added new entry (sum)
•host_cache.lru_cache_replaces: lru cache replaced existing entry (sum)
•host_cache.lru_cache_prunes: lru cache pruned entry to make space for new entry (sum)
•host_cache.lru_cache_find_hits: lru cache found entry in cache (sum)
•host_cache.lru_cache_find_misses: lru cache did not find entry in cache (sum)
•host_cache.lru_cache_removes: lru cache found entry and removed it (sum)
•host_cache.lru_cache_clears: lru cache clear API calls (sum)
6.12 host_tracker
What: configure hosts
Type: basic
Usage: global
Configuration:
• addr host_tracker[].IP = 0.0.0.0/32: hosts address / cidr
• enum host_tracker[].frag_policy: defragmentation policy { first | linux | bsd | bsd_right | last | windows | solaris }
• enum host_tracker[].tcp_policy: TCP reassembly policy { first | last | linux | old_linux | bsd | macos | solaris | irix | hpux11 |
hpux10 | windows | win_2003 | vista | proxy }
• string host_tracker[].services[].name: service identifier
• enum host_tracker[].services[].proto = tcp: IP protocol { tcp | udp }
• port host_tracker[].services[].port: port number
Peg counts:
•host_tracker.service_adds: host service adds (sum)
•host_tracker.service_finds: host service finds (sum)
•host_tracker.service_removes: host service removes (sum)
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6.13 hosts
What: configure hosts
Type: basic
Usage: global
Configuration:
• addr hosts[].ip = 0.0.0.0/32: hosts address / CIDR
• enum hosts[].frag_policy: defragmentation policy { first | linux | bsd | bsd_right | last | windows | solaris }
• enum hosts[].tcp_policy: TCP reassembly policy { first | last | linux | old_linux | bsd | macos | solaris | irix | hpux11 | hpux10 |
windows | win_2003 | vista | proxy }
• string hosts[].services[].name: service identifier
• enum hosts[].services[].proto = tcp: IP protocol { tcp | udp }
• port hosts[].services[].port: port number
6.14 inspection
What: configure basic inspection policy parameters
Type: basic
Usage: inspect
Configuration:
• int inspection.id = 0: correlate policy and events with other items in configuration { 0:65535 }
• string inspection.uuid: correlate events by uuid
• enum inspection.mode = inline-test: set policy mode { inline | inline-test }
6.15 ips
What: configure IPS rule processing
Type: basic
Usage: detect
Configuration:
• bool ips.enable_builtin_rules = false: enable events from builtin rules w/o stubs
• int ips.id = 0: correlate unified2 events with configuration { 0:65535 }
• string ips.include: legacy snort rules and includes
• enum ips.mode: set policy mode { tap | inline | inline-test }
• string ips.rules: snort rules and includes
• string ips.uuid = 00000000-0000-0000-0000-000000000000: IPS policy uuid
Peg counts:
•ips.invalid_policy_ids: Number of times an invalid policy ID was provided (sum)
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6.16 latency
What: packet and rule latency monitoring and control
Type: basic
Usage: context
Configuration:
• int latency.packet.max_time = 500: set timeout for packet latency thresholding (usec) { 0: }
• bool latency.packet.fastpath = false: fastpath expensive packets (max_time exceeded)
• enum latency.packet.action = none: event action if packet times out and is fastpathed { none | alert | log | alert_and_log }
• int latency.rule.max_time = 500: set timeout for rule evaluation (usec) { 0: }
• bool latency.rule.suspend = false: temporarily suspend expensive rules
• int latency.rule.suspend_threshold = 5: set threshold for number of timeouts before suspending a rule { 1: }
• int latency.rule.max_suspend_time = 30000: set max time for suspending a rule (ms, 0 means permanently disable rule) { 0:
}
• enum latency.rule.action = none: event action for rule latency enable and suspend events { none | alert | log | alert_and_log }
Rules:
•134:1 (latency) rule tree suspended due to latency
•134:2 (latency) rule tree re-enabled after suspend timeout
•134:3 (latency) packet fastpathed due to latency
Peg counts:
•latency.total_packets: total packets monitored (sum)
•latency.total_usecs: total usecs elapsed (sum)
•latency.max_usecs: maximum usecs elapsed (sum)
•latency.packet_timeouts: packets that timed out (sum)
•latency.total_rule_evals: total rule evals monitored (sum)
•latency.rule_eval_timeouts: rule evals that timed out (sum)
•latency.rule_tree_enables: rule tree re-enables (sum)
6.17 memory
What: memory management configuration
Type: basic
Usage: global
Configuration:
• int memory.cap = 0: set the per-packet-thread cap on memory (bytes, 0 to disable) { 0: }
• bool memory.soft = false: always succeed in allocating memory, even if above the cap
• int memory.threshold = 0: set the per-packet-thread threshold for preemptive cleanup actions (percent, 0 to disable) { 0: }
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6.18 network
What: configure basic network parameters
Type: basic
Usage: context
Configuration:
• multi network.checksum_drop = none: drop if checksum is bad { all | ip | noip | tcp | notcp | udp | noudp | icmp | noicmp |
none }
• multi network.checksum_eval = none: checksums to verify { all | ip | noip | tcp | notcp | udp | noudp | icmp | noicmp | none }
• bool network.decode_drops = false: enable dropping of packets by the decoder
• int network.id = 0: correlate unified2 events with configuration { 0:65535 }
• int network.min_ttl = 1: alert / normalize packets with lower TTL / hop limit (you must enable rules and / or normalization
also) { 1:255 }
• int network.new_ttl = 1: use this value for responses and when normalizing { 1:255 }
• int network.layers = 40: the maximum number of protocols that Snort can correctly decode { 3:255 }
• int network.max_ip6_extensions = 0: the maximum number of IP6 options Snort will process for a given IPv6 layer before
raising 116:456 (0 = unlimited) { 0:255 }
• int network.max_ip_layers = 0: the maximum number of IP layers Snort will process for a given packet before raising 116:293
(0 = unlimited) { 0:255 }
6.19 output
What: configure general output parameters
Type: basic
Usage: global
Configuration:
• bool output.dump_chars_only = false: turns on character dumps (same as -C)
• bool output.dump_payload = false: dumps application layer (same as -d)
• bool output.dump_payload_verbose = false: dumps raw packet starting at link layer (same as -X)
• int output.event_trace.max_data = 0: maximum amount of packet data to capture { 0:65535 }
• bool output.quiet = false: suppress non-fatal information (still show alerts, same as -q)
• string output.logdir = .: where to put log files (same as -l)
• bool output.obfuscate = false: obfuscate the logged IP addresses (same as -O)
• bool output.obfuscate_pii = false: mask all but the last 4 characters of credit card and social security numbers
• bool output.show_year = false: include year in timestamp in the alert and log files (same as -y)
• int output.tagged_packet_limit = 256: maximum number of packets tagged for non-packet metrics { 0: }
• bool output.verbose = false: be verbose (same as -v)
• bool output.wide_hex_dump = true: output 20 bytes per lines instead of 16 when dumping buffers
• bool output.enable_packet_trace = false: enable summary output of state that determined packet verdict
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6.20 packets
What: configure basic packet handling
Type: basic
Usage: global
Configuration:
• bool packets.address_space_agnostic = false: determines whether DAQ address space info is used to track fragments and
connections
• string packets.bpf_file: file with BPF to select traffic for Snort
• int packets.limit = 0: maximum number of packets to process before stopping (0 is unlimited) { 0: }
• int packets.skip = 0: number of packets to skip before before processing { 0: }
• bool packets.vlan_agnostic = false: determines whether VLAN info is used to track fragments and connections
6.21 process
What: configure basic process setup
Type: basic
Usage: global
Configuration:
• string process.chroot: set chroot directory (same as -t)
• string process.threads[].cpuset: pin the associated thread to this cpuset
• int process.threads[].thread = 0: set cpu affinity for the <cur_thread_num> thread that runs { 0: }
• bool process.daemon = false: fork as a daemon (same as -D)
• bool process.dirty_pig = false: shutdown without internal cleanup
• string process.set_gid: set group ID (same as -g)
• string process.set_uid: set user ID (same as -u)
• string process.umask: set process umask (same as -m)
• bool process.utc = false: use UTC instead of local time for timestamps
6.22 profiler
What: configure profiling of rules and/or modules
Type: basic
Usage: global
Configuration:
• bool profiler.modules.show = true: show module time profile stats
• int profiler.modules.count = 0: limit results to count items per level (0 = no limit) { 0: }
• enum profiler.modules.sort = total_time: sort by given field { none | checks | avg_check | total_time }
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• int profiler.modules.max_depth = -1: limit depth to max_depth (-1 = no limit) { -1: }
• bool profiler.memory.show = true: show module memory profile stats
• int profiler.memory.count = 0: limit results to count items per level (0 = no limit) { 0: }
• enum profiler.memory.sort = total_used: sort by given field { none | allocations | total_used | avg_allocation }
• int profiler.memory.max_depth = -1: limit depth to max_depth (-1 = no limit) { -1: }
• bool profiler.rules.show = true: show rule time profile stats
• int profiler.rules.count = 0: print results to given level (0 = all) { 0: }
• enum profiler.rules.sort = total_time: sort by given field { none | checks | avg_check | total_time | matches | no_matches |
avg_match | avg_no_match }
6.23 rate_filter
What: configure rate filters (which change rule actions)
Type: basic
Usage: detect
Configuration:
• int rate_filter[].gid = 1: rule generator ID { 0: }
• int rate_filter[].sid = 1: rule signature ID { 0: }
• enum rate_filter[].track = by_src: filter only matching source or destination addresses { by_src | by_dst | by_rule }
• int rate_filter[].count = 1: number of events in interval before tripping { 0: }
• int rate_filter[].seconds = 1: count interval { 0: }
• enum rate_filter[].new_action = alert: take this action on future hits until timeout { log | pass | alert | drop | block | reset }
• int rate_filter[].timeout = 1: count interval { 0: }
• string rate_filter[].apply_to: restrict filter to these addresses according to track
6.24 references
What: define reference systems used in rules
Type: basic
Usage: global
Configuration:
• string references[].name: name used with reference rule option
• string references[].url: where this reference is defined
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6.25 rule_state
What: enable/disable specific IPS rules
Type: basic
Usage: detect
Configuration:
• int rule_state.gid = 0: rule generator ID { 0: }
• int rule_state.sid = 0: rule signature ID { 0: }
• bool rule_state.enable = true: enable or disable rule in all policies
6.26 search_engine
What: configure fast pattern matcher
Type: basic
Usage: global
Configuration:
• int search_engine.bleedover_port_limit = 1024: maximum ports in rule before demotion to any-any port group { 1: }
• bool search_engine.bleedover_warnings_enabled = false: print warning if a rule is demoted to any-any port group
• bool search_engine.enable_single_rule_group = false: put all rules into one group
• bool search_engine.debug = false: print verbose fast pattern info
• bool search_engine.debug_print_nocontent_rule_tests = false: print rule group info during packet evaluation
• bool search_engine.debug_print_rule_group_build_details = false: print rule group info during compilation
• bool search_engine.debug_print_rule_groups_uncompiled = false: prints uncompiled rule group information
• bool search_engine.debug_print_rule_groups_compiled = false: prints compiled rule group information
• int search_engine.max_pattern_len = 0: truncate patterns when compiling into state machine (0 means no maximum) { 0: }
• int search_engine.max_queue_events = 5: maximum number of matching fast pattern states to queue per packet { 2:100 }
• bool search_engine.detect_raw_tcp = true: detect on TCP payload before reassembly
• dynamic search_engine.search_method = ac_bnfa: set fast pattern algorithm - choose available search engine { ac_banded |
ac_bnfa | ac_full | ac_sparse | ac_sparse_bands | ac_std | hyperscan }
• bool search_engine.search_optimize = true: tweak state machine construction for better performance
• bool search_engine.show_fast_patterns = false: print fast pattern info for each rule
• bool search_engine.split_any_any = true: evaluate any-any rules separately to save memory
Peg counts:
•search_engine.max_queued: maximum fast pattern matches queued for further evaluation (sum)
•search_engine.total_flushed: fast pattern matches discarded due to overflow (sum)
•search_engine.total_inserts: total fast pattern hits (sum)
•search_engine.total_unique: total unique fast pattern hits (sum)
•search_engine.non_qualified_events: total non-qualified events (sum)
•search_engine.qualified_events: total qualified events (sum)
•search_engine.searched_bytes: total bytes searched (sum)
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6.27 side_channel
What: implement the side-channel asynchronous messaging subsystem
Type: basic
Usage: global
Configuration:
• bit_list side_channel.ports: side channel message port list { 65535 }
• string side_channel.connectors[].connector: connector handle
• string side_channel.connector: connector handle
Peg counts:
•side_channel.packets: total packets (sum)
6.28 snort
What: command line configuration and shell commands
Type: basic
Usage: global
Configuration:
• string snort.-?: <option prefix> output matching command line option quick help (same as --help-options) { (optional) }
• string snort.-A: <mode> set alert mode: none, cmg, or alert_*
• addr snort.-B = 255.255.255.255/32: <mask> obfuscated IP addresses in alerts and packet dumps using CIDR mask
• implied snort.-C: print out payloads with character data only (no hex)
• string snort.-c: <conf> use this configuration
• implied snort.-D: run Snort in background (daemon) mode
• implied snort.-d: dump the Application Layer
• implied snort.-e: display the second layer header info
• implied snort.-f: turn off fflush() calls after binary log writes
• int snort.-G: <0xid> (same as --logid) { 0:65535 }
• string snort.-g: <gname> run snort gid as <gname> group (or gid) after initialization
• implied snort.-H: make hash tables deterministic
• string snort.-i: <iface>. . . list of interfaces
• port snort.-j: <port> to listen for Telnet connections
• enum snort.-k = all: <mode> checksum mode; default is all { all|noip|notcp|noudp|noicmp|none }
• string snort.-L: <mode> logging mode (none, dump, pcap, or log_*)
• string snort.-l: <logdir> log to this directory instead of current directory
• implied snort.-M: log messages to syslog (not alerts)
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• int snort.-m: <umask> set umask = <umask> { 0: }
• int snort.-n: <count> stop after count packets { 0: }
• implied snort.-O: obfuscate the logged IP addresses
• implied snort.-Q: enable inline mode operation
• implied snort.-q: quiet mode - Don’t show banner and status report
• string snort.-R: <rules> include this rules file in the default policy
• string snort.-r: <pcap>. . . (same as --pcap-list)
• string snort.-S: <x=v> set config variable x equal to value v
• int snort.-s = 1514: <snap> (same as --snaplen); default is 1514 { 68:65535 }
• implied snort.-T: test and report on the current Snort configuration
• string snort.-t: <dir> chroots process to <dir> after initialization
• implied snort.-U: use UTC for timestamps
• string snort.-u: <uname> run snort as <uname> or <uid> after initialization
• implied snort.-V: (same as --version)
• implied snort.-v: be verbose
• implied snort.-W: lists available interfaces
• implied snort.-X: dump the raw packet data starting at the link layer
• implied snort.-x: same as --pedantic
• implied snort.-y: include year in timestamp in the alert and log files
• int snort.-z = 1: <count> maximum number of packet threads (same as --max-packet-threads); 0 gets the number of CPU cores
reported by the system; default is 1 { 0: }
• implied snort.--alert-before-pass: process alert, drop, sdrop, or reject before pass; default is pass before alert, drop,. . .
• string snort.--bpf: <filter options> are standard BPF options, as seen in TCPDump
• string snort.--c2x: output hex for given char (see also --x2c)
• string snort.--control-socket: <file> to create unix socket
• implied snort.--create-pidfile: create PID file, even when not in Daemon mode
• string snort.--daq: <type> select packet acquisition module (default is pcap)
• string snort.--daq-dir: <dir> tell snort where to find desired DAQ
• implied snort.--daq-list: list packet acquisition modules available in optional dir, default is static modules only
• string snort.--daq-var: <name=value> specify extra DAQ configuration variable
• implied snort.--dirty-pig: don’t flush packets on shutdown
• string snort.--dump-builtin-rules: [<module prefix>] output stub rules for selected modules { (optional) }
• implied snort.--dump-dynamic-rules: output stub rules for all loaded rules libraries
• string snort.--dump-defaults: [<module prefix>] output module defaults in Lua format { (optional) }
• implied snort.--dump-version: output the version, the whole version, and only the version
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• implied snort.--enable-inline-test: enable Inline-Test Mode Operation
• implied snort.--gen-msg-map: dump builtin rules in gen-msg.map format for use by other tools
• implied snort.--help: list command line options
• string snort.--help-commands: [<module prefix>] output matching commands { (optional) }
• string snort.--help-config: [<module prefix>] output matching config options { (optional) }
• string snort.--help-counts: [<module prefix>] output matching peg counts { (optional) }
• string snort.--help-module: <module> output description of given module
• implied snort.--help-modules: list all available modules with brief help
• string snort.--help-options: [<option prefix>] output matching command line option quick help (same as -?) { (optional) }
• implied snort.--help-plugins: list all available plugins with brief help
• implied snort.--help-signals: dump available control signals
• int snort.--id-offset = 0: offset to add to instance IDs when logging to files { 0:65535 }
• implied snort.--id-subdir: create/use instance subdirectories in logdir instead of instance filename prefix
• implied snort.--id-zero: use id prefix / subdirectory even with one packet thread
• implied snort.--list-buffers: output available inspection buffers
• string snort.--list-builtin: [<module prefix>] output matching builtin rules { (optional) }
• string snort.--list-gids: [<module prefix>] output matching generators { (optional) }
• string snort.--list-modules: [<module type>] list all known modules of given type { (optional) }
• implied snort.--list-plugins: list all known plugins
• string snort.--lua: <chunk> extend/override conf with chunk; may be repeated
• int snort.--logid: <0xid> log Identifier to uniquely id events for multiple snorts (same as -G) { 0:65535 }
• implied snort.--markup: output help in asciidoc compatible format
• int snort.--max-packet-threads = 1: <count> configure maximum number of packet threads (same as -z) { 0: }
• implied snort.--mem-check: like -T but also compile search engines
• implied snort.--nostamps: don’t include timestamps in log file names
• implied snort.--nolock-pidfile: do not try to lock Snort PID file
• implied snort.--pause: wait for resume/quit command before processing packets/terminating
• implied snort.--parsing-follows-files: parse relative paths from the perspective of the current configuration file
• string snort.--pcap-file: <file> file that contains a list of pcaps to read - read mode is implied
• string snort.--pcap-list: <list> a space separated list of pcaps to read - read mode is implied
• string snort.--pcap-dir: <dir> a directory to recurse to look for pcaps - read mode is implied
• string snort.--pcap-filter: <filter> filter to apply when getting pcaps from file or directory
• int snort.--pcap-loop: <count> read all pcaps <count> times; 0 will read until Snort is terminated { -1: }
• implied snort.--pcap-no-filter: reset to use no filter when getting pcaps from file or directory
• implied snort.--pcap-reload: if reading multiple pcaps, reload snort config between pcaps
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• implied snort.--pcap-show: print a line saying what pcap is currently being read
• implied snort.--pedantic: warnings are fatal
• string snort.--plugin-path: <path> where to find plugins
• implied snort.--process-all-events: process all action groups
• string snort.--rule: <rules> to be added to configuration; may be repeated
• implied snort.--rule-to-hex: output so rule header to stdout for text rule on stdin
• implied snort.--rule-to-text: output plain so rule header to stdout for text rule on stdin
• string snort.--run-prefix: <pfx> prepend this to each output file
• string snort.--script-path: <path> to a luajit script or directory containing luajit scripts
• implied snort.--shell: enable the interactive command line
• implied snort.--piglet: enable piglet test harness mode
• implied snort.--show-plugins: list module and plugin versions
• int snort.--skip: <n> skip 1st n packets { 0: }
• int snort.--snaplen = 1514: <snap> set snaplen of packet (same as -s) { 68:65535 }
• implied snort.--stdin-rules: read rules from stdin until EOF or a line starting with END is read
• implied snort.--treat-drop-as-alert: converts drop, sdrop, and reject rules into alert rules during startup
• implied snort.--treat-drop-as-ignore: use drop, sdrop, and reject rules to ignore session traffic when not inline
• string snort.--catch-test: comma separated list of cat unit test tags or all
• implied snort.--version: show version number (same as -V)
• implied snort.--warn-all: enable all warnings
• implied snort.--warn-conf: warn about configuration issues
• implied snort.--warn-daq: warn about DAQ issues, usually related to mode
• implied snort.--warn-flowbits: warn about flowbits that are checked but not set and vice-versa
• implied snort.--warn-hosts: warn about host table issues
• implied snort.--warn-plugins: warn about issues that prevent plugins from loading
• implied snort.--warn-rules: warn about duplicate rules and rule parsing issues
• implied snort.--warn-scripts: warn about issues discovered while processing Lua scripts
• implied snort.--warn-symbols: warn about unknown symbols in your Lua config
• implied snort.--warn-vars: warn about variable definition and usage issues
• int snort.--x2c: output ASCII char for given hex (see also --c2x)
• string snort.--x2s: output ASCII string for given byte code (see also --x2c)
Commands:
•snort.show_plugins(): show available plugins
•snort.delete_inspector(inspector): delete an inspector from the default policy
Snort 3 User Manual 81 / 284
•snort.dump_stats(): show summary statistics
•snort.rotate_stats(): roll perfmonitor log files
•snort.reload_config(filename): load new configuration
•snort.reload_policy(filename): reload part or all of the default policy
•snort.reload_daq(): reload daq module
•snort.reload_hosts(filename): load a new hosts table
•snort.pause(): suspend packet processing
•snort.resume(): continue packet processing
•snort.detach(): exit shell w/o shutdown
•snort.quit(): shutdown and dump-stats
•snort.help(): this output
Peg counts:
•snort.local_commands: total local commands processed (sum)
•snort.remote_commands: total remote commands processed (sum)
•snort.signals: total signals processed (sum)
•snort.conf_reloads: number of times configuration was reloaded (sum)
•snort.policy_reloads: number of times policies were reloaded (sum)
•snort.inspector_deletions: number of times inspectors were deleted (sum)
•snort.daq_reloads: number of times daq configuration was reloaded (sum)
•snort.attribute_table_reloads: number of times hosts table was reloaded (sum)
•snort.attribute_table_hosts: total number of hosts in table (sum)
6.29 suppress
What: configure event suppressions
Type: basic
Usage: detect
Configuration:
• int suppress[].gid = 0: rule generator ID { 0: }
• int suppress[].sid = 0: rule signature ID { 0: }
• enum suppress[].track: suppress only matching source or destination addresses { by_src | by_dst }
• string suppress[].ip: restrict suppression to these addresses according to track
7 Codec Modules
Codec is short for coder / decoder. These modules are used for basic protocol decoding, anomaly detection, and construction of
active responses.
Snort 3 User Manual 82 / 284
7.1 arp
What: support for address resolution protocol
Type: codec
Usage: context
Rules:
•116:109 (arp) truncated ARP
7.2 auth
What: support for IP authentication header
Type: codec
Usage: context
Rules:
•116:465 (auth) truncated authentication header
•116:466 (auth) bad authentication header length
7.3 ciscometadata
What: support for cisco metadata
Type: codec
Usage: context
Rules:
•116:468 (ciscometadata) truncated Cisco Metadata header
•116:469 (ciscometadata) invalid Cisco Metadata option length
•116:470 (ciscometadata) invalid Cisco Metadata option type
•116:471 (ciscometadata) invalid Cisco Metadata SGT
7.4 eapol
What: support for extensible authentication protocol over LAN
Type: codec
Usage: context
Rules:
•116:110 (eapol) truncated EAP header
•116:111 (eapol) EAP key truncated
•116:112 (eapol) EAP header truncated
Snort 3 User Manual 83 / 284
7.5 erspan2
What: support for encapsulated remote switched port analyzer - type 2
Type: codec
Usage: context
Rules:
•116:462 (erspan2) ERSpan header version mismatch
•116:463 (erspan2) captured length < ERSpan type2 header length
7.6 erspan3
What: support for encapsulated remote switched port analyzer - type 3
Type: codec
Usage: context
Rules:
•116:464 (erspan3) captured < ERSpan type3 header length
7.7 esp
What: support for encapsulating security payload
Type: codec
Usage: context
Configuration:
• bool esp.decode_esp = false: enable for inspection of esp traffic that has authentication but not encryption
Rules:
•116:294 (esp) truncated encapsulated security payload header
7.8 eth
What: support for ethernet protocol (DLT 1) (DLT 51)
Type: codec
Usage: context
Rules:
•116:424 (eth) truncated ethernet header
7.9 fabricpath
What: support for fabricpath
Type: codec
Usage: context
Rules:
•116:467 (fabricpath) truncated FabricPath header
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7.10 gre
What: support for generic routing encapsulation
Type: codec
Usage: context
Rules:
•116:160 (gre) GRE header length > payload length
•116:161 (gre) multiple encapsulations in packet
•116:162 (gre) invalid GRE version
•116:163 (gre) invalid GRE header
•116:164 (gre) invalid GRE v.1 PPTP header
•116:165 (gre) GRE trans header length > payload length
7.11 gtp
What: support for general-packet-radio-service tunneling protocol
Type: codec
Usage: context
Rules:
•116:297 (gtp) two or more GTP encapsulation layers present
•116:298 (gtp) GTP header length is invalid
7.12 icmp4
What: support for Internet control message protocol v4
Type: codec
Usage: context
Rules:
•116:105 (icmp4) ICMP header truncated
•116:106 (icmp4) ICMP timestamp header truncated
•116:107 (icmp4) ICMP address header truncated
•116:250 (icmp4) ICMP original IP header truncated
•116:251 (icmp4) ICMP version and original IP header versions differ
•116:252 (icmp4) ICMP original datagram length < original IP header length
•116:253 (icmp4) ICMP original IP payload < 64 bits
•116:254 (icmp4) ICMP original IP payload > 576 bytes
•116:255 (icmp4) ICMP original IP fragmented and offset not 0
•116:415 (icmp4) ICMP4 packet to multicast dest address
Snort 3 User Manual 85 / 284
•116:416 (icmp4) ICMP4 packet to broadcast dest address
•116:418 (icmp4) ICMP4 type other
•116:434 (icmp4) ICMP ping Nmap
•116:435 (icmp4) ICMP icmpenum v1.1.1
•116:436 (icmp4) ICMP redirect host
•116:437 (icmp4) ICMP redirect net
•116:438 (icmp4) ICMP traceroute ipopts
•116:439 (icmp4) ICMP source quench
•116:440 (icmp4) broadscan smurf scanner
•116:441 (icmp4) ICMP destination unreachable communication administratively prohibited
•116:442 (icmp4) ICMP destination unreachable communication with destination host is administratively prohibited
•116:443 (icmp4) ICMP destination unreachable communication with destination network is administratively prohibited
•116:451 (icmp4) ICMP path MTU denial of service attempt
•116:452 (icmp4) Linux ICMP header DOS attempt
•116:426 (icmp4) truncated ICMP4 header
Peg counts:
•icmp4.bad_checksum: non-zero icmp checksums (sum)
7.13 icmp6
What: support for Internet control message protocol v6
Type: codec
Usage: context
Rules:
•116:427 (icmp6) truncated ICMPv6 header
•116:431 (icmp6) ICMPv6 type not decoded
•116:432 (icmp6) ICMPv6 packet to multicast address
•116:285 (icmp6) ICMPv6 packet of type 2 (message too big) with MTU field < 1280
•116:286 (icmp6) ICMPv6 packet of type 1 (destination unreachable) with non-RFC 2463 code
•116:287 (icmp6) ICMPv6 router solicitation packet with a code not equal to 0
•116:288 (icmp6) ICMPv6 router advertisement packet with a code not equal to 0
•116:289 (icmp6) ICMPv6 router solicitation packet with the reserved field not equal to 0
•116:290 (icmp6) ICMPv6 router advertisement packet with the reachable time field set > 1 hour
•116:457 (icmp6) ICMPv6 packet of type 1 (destination unreachable) with non-RFC 4443 code
•116:460 (icmp6) ICMPv6 node info query/response packet with a code greater than 2
•116:474 (icmp6) ICMPv6 not encapsulated in IPv6
Peg counts:
•icmp6.bad_icmp6_checksum: nonzero icmp6 checksums (sum)
Snort 3 User Manual 86 / 284
7.14 igmp
What: support for Internet group management protocol
Type: codec
Usage: context
Rules:
•116:455 (igmp) DOS IGMP IP options validation attempt
7.15 ipv4
What: support for Internet protocol v4
Type: codec
Usage: context
Rules:
•116:1 (ipv4) not IPv4 datagram
•116:2 (ipv4) IPv4 header length < minimum
•116:3 (ipv4) IPv4 datagram length < header field
•116:4 (ipv4) IPv4 options found with bad lengths
•116:5 (ipv4) truncated IPv4 options
•116:6 (ipv4) IPv4 datagram length > captured length
•116:404 (ipv4) IPv4 packet with zero TTL
•116:405 (ipv4) IPv4 packet with bad frag bits (both MF and DF set)
•116:407 (ipv4) IPv4 packet frag offset + length exceed maximum
•116:408 (ipv4) IPv4 packet from current net source address
•116:409 (ipv4) IPv4 packet to current net dest address
•116:410 (ipv4) IPv4 packet from multicast source address
•116:411 (ipv4) IPv4 packet from reserved source address
•116:412 (ipv4) IPv4 packet to reserved dest address
•116:413 (ipv4) IPv4 packet from broadcast source address
•116:414 (ipv4) IPv4 packet to broadcast dest address
•116:428 (ipv4) IPv4 packet below TTL limit
•116:430 (ipv4) IPv4 packet both DF and offset set
•116:448 (ipv4) IPv4 reserved bit set
•116:444 (ipv4) IPv4 option set
•116:425 (ipv4) truncated IPv4 header
Peg counts:
•ipv4.bad_checksum: nonzero ip checksums (sum)
Snort 3 User Manual 87 / 284
7.16 ipv6
What: support for Internet protocol v6
Type: codec
Usage: context
Rules:
•116:270 (ipv6) IPv6 packet below TTL limit
•116:271 (ipv6) IPv6 header claims to not be IPv6
•116:272 (ipv6) IPv6 truncated extension header
•116:273 (ipv6) IPv6 truncated header
•116:274 (ipv6) IPv6 datagram length < header field
•116:275 (ipv6) IPv6 datagram length > captured length
•116:276 (ipv6) IPv6 packet with destination address ::0
•116:277 (ipv6) IPv6 packet with multicast source address
•116:278 (ipv6) IPv6 packet with reserved multicast destination address
•116:279 (ipv6) IPv6 header includes an undefined option type
•116:280 (ipv6) IPv6 address includes an unassigned multicast scope value
•116:281 (ipv6) IPv6 header includes an invalid value for the next header field
•116:282 (ipv6) IPv6 header includes a routing extension header followed by a hop-by-hop header
•116:283 (ipv6) IPv6 header includes two routing extension headers
•116:292 (ipv6) IPv6 header has destination options followed by a routing header
•116:291 (ipv6) IPV6 tunneled over IPv4, IPv6 header truncated, possible Linux kernel attack
•116:295 (ipv6) IPv6 header includes an option which is too big for the containing header
•116:296 (ipv6) IPv6 packet includes out-of-order extension headers
•116:429 (ipv6) IPv6 packet has zero hop limit
•116:453 (ipv6) ISATAP-addressed IPv6 traffic spoofing attempt
•116:458 (ipv6) bogus fragmentation packet, possible BSD attack
•116:461 (ipv6) IPv6 routing type 0 extension header
•116:456 (ipv6) too many IPv6 extension headers
•116:475 (ipv6) IPv6 mobility header includes an invalid value for the payload protocol field
7.17 llc
What: support for logical link control
Type: codec
Usage: context
Rules:
•116:131 (llc) bad LLC header
•116:132 (llc) bad extra LLC info
Snort 3 User Manual 88 / 284
7.18 mpls
What: support for multiprotocol label switching
Type: codec
Usage: context
Configuration:
• bool mpls.enable_mpls_multicast = false: enables support for MPLS multicast
• bool mpls.enable_mpls_overlapping_ip = false: enable if private network addresses overlap and must be differentiated by
MPLS label(s)
• int mpls.max_mpls_stack_depth = -1: set MPLS stack depth { -1: }
• enum mpls.mpls_payload_type = ip4: set encapsulated payload type { eth | ip4 | ip6 }
Rules:
•116:170 (mpls) bad MPLS frame
•116:171 (mpls) MPLS label 0 appears in non-bottom header
•116:172 (mpls) MPLS label 1 appears in bottom header
•116:173 (mpls) MPLS label 2 appears in non-bottom header
•116:174 (mpls) MPLS label 3 appears in header
•116:175 (mpls) MPLS label 4, 5,.. or 15 appears in header
•116:176 (mpls) too many MPLS headers
Peg counts:
•mpls.total_packets: total mpls labeled packets processed (sum)
•mpls.total_bytes: total mpls labeled bytes processed (sum)
7.19 pbb
What: support for 802.1ah protocol
Type: codec
Usage: context
Rules:
•116:424 (pbb) truncated ethernet header
7.20 pgm
What: support for pragmatic general multicast
Type: codec
Usage: context
Rules:
•116:454 (pgm) PGM nak list overflow attempt
Snort 3 User Manual 89 / 284
7.21 pppoe
What: support for point-to-point protocol over ethernet
Type: codec
Usage: context
Rules:
•116:120 (pppoe) bad PPPOE frame detected
7.22 tcp
What: support for transmission control protocol
Type: codec
Usage: context
Rules:
•116:45 (tcp) TCP packet length is smaller than 20 bytes
•116:46 (tcp) TCP data offset is less than 5
•116:47 (tcp) TCP header length exceeds packet length
•116:54 (tcp) TCP options found with bad lengths
•116:55 (tcp) truncated TCP options
•116:56 (tcp) T/TCP detected
•116:57 (tcp) obsolete TCP options found
•116:58 (tcp) experimental TCP options found
•116:59 (tcp) TCP window scale option found with length > 14
•116:400 (tcp) XMAS attack detected
•116:401 (tcp) Nmap XMAS attack detected
•116:419 (tcp) TCP urgent pointer exceeds payload length or no payload
•116:420 (tcp) TCP SYN with FIN
•116:421 (tcp) TCP SYN with RST
•116:422 (tcp) TCP PDU missing ack for established session
•116:423 (tcp) TCP has no SYN, ACK, or RST
•116:433 (tcp) DDOS shaft SYN flood
•116:446 (tcp) TCP port 0 traffic
•116:402 (tcp) DOS NAPTHA vulnerability detected
•116:403 (tcp) SYN to multicast address
Peg counts:
•tcp.bad_tcp4_checksum: nonzero tcp over ip checksums (sum)
•tcp.bad_tcp6_checksum: nonzero tcp over ipv6 checksums (sum)
Snort 3 User Manual 90 / 284
7.23 token_ring
What: support for token ring decoding
Type: codec
Usage: context
Rules:
•116:140 (token_ring) bad Token Ring header
•116:141 (token_ring) bad Token Ring ETHLLC header
•116:142 (token_ring) bad Token Ring MRLEN header
•116:143 (token_ring) bad Token Ring MR header
7.24 udp
What: support for user datagram protocol
Type: codec
Usage: context
Configuration:
• bool udp.deep_teredo_inspection = false: look for Teredo on all UDP ports (default is only 3544)
• bool udp.enable_gtp = false: decode GTP encapsulations
• bit_list udp.gtp_ports = 2152 3386: set GTP ports { 65535 }
Rules:
•116:95 (udp) truncated UDP header
•116:96 (udp) invalid UDP header, length field < 8
•116:97 (udp) short UDP packet, length field > payload length
•116:98 (udp) long UDP packet, length field < payload length
•116:406 (udp) invalid IPv6 UDP packet, checksum zero
•116:445 (udp) large UDP packet (> 4000 bytes)
•116:447 (udp) UDP port 0 traffic
Peg counts:
•udp.bad_udp4_checksum: nonzero udp over ipv4 checksums (sum)
•udp.bad_udp6_checksum: nonzero udp over ipv6 checksums (sum)
7.25 vlan
What: support for local area network
Type: codec
Usage: context
Rules:
•116:130 (vlan) bad VLAN frame
Snort 3 User Manual 91 / 284
7.26 wlan
What: support for wireless local area network protocol (DLT 105)
Type: codec
Usage: context
Rules:
•116:133 (wlan) bad 802.11 LLC header
•116:134 (wlan) bad 802.11 extra LLC info
8 Connector Modules
Connectors support High Availability communication links.
8.1 file_connector
What: implement the file based connector
Type: connector
Usage: global
Configuration:
• string file_connector.connector: connector name
• string file_connector.name: channel name
• enum file_connector.format: file format { binary | text }
• enum file_connector.direction: usage { receive | transmit | duplex }
Peg counts:
•file_connector.messages: total messages (sum)
8.2 tcp_connector
What: implement the tcp stream connector
Type: connector
Usage: global
Configuration:
• string tcp_connector.connector: connector name
• string tcp_connector.address: address
• port tcp_connector.base_port: base port number
• enum tcp_connector.setup: stream establishment { call | answer }
Peg counts:
•tcp_connector.messages: total messages (sum)
Snort 3 User Manual 92 / 284
9 Inspector Modules
These modules perform a variety of functions, including analysis of protocols beyond basic decoding.
9.1 appid
What: application and service identification
Type: inspector
Usage: context
Configuration:
• int appid.memcap = 0: disregard - not implemented { 0: }
• bool appid.log_stats = false: enable logging of appid statistics
• int appid.app_stats_period = 300: time period for collecting and logging appid statistics { 0: }
• int appid.app_stats_rollover_size = 20971520: max file size for appid stats before rolling over the log file { 0: }
• int appid.app_stats_rollover_time = 86400: max time period for collection appid stats before rolling over the log file { 0: }
• string appid.app_detector_dir: directory to load appid detectors from
• int appid.instance_id = 0: instance id - ignored { 0: }
• bool appid.debug = false: enable appid debug logging
• bool appid.dump_ports = false: enable dump of appid port information
• addr appid.session_log_filter.src_ip = 0.0.0.0/32: source IP address in CIDR format
• addr appid.session_log_filter.dst_ip = 0.0.0.0/32: destination IP address in CIDR format
• port appid.session_log_filter.src_port: source port { 1: }
• port appid.session_log_filter.dst_port: destination port { 1: }
• string appid.session_log_filter.protocol: IP protocol
• bool appid.session_log_filter.log_all_sessions = false: enable logging for all appid sessions
• bool appid.log_all_sessions = false: enable logging of all appid sessions
9.2 arp_spoof
What: detect ARP attacks and anomalies
Type: inspector
Usage: inspect
Configuration:
• ip4 arp_spoof.hosts[].ip: host ip address
• mac arp_spoof.hosts[].mac: host mac address
Rules:
•112:1 (arp_spoof) unicast ARP request
Snort 3 User Manual 93 / 284
•112:2 (arp_spoof) ethernet/ARP mismatch request for source
•112:3 (arp_spoof) ethernet/ARP mismatch request for destination
•112:4 (arp_spoof) attempted ARP cache overwrite attack
Peg counts:
•arp_spoof.packets: total packets (sum)
9.3 back_orifice
What: back orifice detection
Type: inspector
Usage: inspect
Rules:
•105:1 (back_orifice) BO traffic detected
•105:2 (back_orifice) BO client traffic detected
•105:3 (back_orifice) BO server traffic detected
•105:4 (back_orifice) BO Snort buffer attack
Peg counts:
•back_orifice.packets: total packets (sum)
9.4 binder
What: configure processing based on CIDRs, ports, services, etc.
Type: inspector
Usage: inspect
Configuration:
• int binder[].when.ips_policy_id = 0: unique ID for selection of this config by external logic { 0: }
• bit_list binder[].when.ifaces: list of interface indices { 255 }
• bit_list binder[].when.vlans: list of VLAN IDs { 4095 }
• addr_list binder[].when.nets: list of networks
• addr_list binder[].when.src_nets: list of source networks
• addr_list binder[].when.dst_nets: list of destination networks
• enum binder[].when.proto: protocol { any | ip | icmp | tcp | udp | user | file }
• bit_list binder[].when.ports: list of ports { 65535 }
• bit_list binder[].when.src_ports: list of source ports { 65535 }
• bit_list binder[].when.dst_ports: list of destination ports { 65535 }
• int binder[].when.src_zone: source zone { 0:2147483647 }
Snort 3 User Manual 94 / 284
• int binder[].when.dst_zone: destination zone { 0:2147483647 }
• enum binder[].when.role = any: use the given configuration on one or any end of a session { client | server | any }
• string binder[].when.service: override default configuration
• enum binder[].use.action = inspect: what to do with matching traffic { reset | block | allow | inspect }
• string binder[].use.file: use configuration in given file
• string binder[].use.inspection_policy: use inspection policy from given file
• string binder[].use.ips_policy: use ips policy from given file
• string binder[].use.network_policy: use network policy from given file
• string binder[].use.service: override automatic service identification
• string binder[].use.type: select module for binding
• string binder[].use.name: symbol name (defaults to type)
Peg counts:
•binder.packets: initial bindings (sum)
•binder.resets: reset bindings (sum)
•binder.blocks: block bindings (sum)
•binder.allows: allow bindings (sum)
•binder.inspects: inspect bindings (sum)
9.5 data_log
What: log selected published data to data.log
Type: inspector
Usage: inspect
Configuration:
• select data_log.key = http_request_header_event : name of the event to log { http_request_header_event | http_response_header_event
}
• int data_log.limit = 0: set maximum size in MB before rollover (0 is unlimited) { 0: }
Peg counts:
•data_log.packets: total packets (sum)
9.6 dce_http_proxy
What: dce over http inspection - client to/from proxy
Type: inspector
Usage: inspect
Peg counts:
•dce_http_proxy.http_proxy_sessions: successful http proxy sessions (sum)
•dce_http_proxy.http_proxy_session_failures: failed http proxy sessions (sum)
Snort 3 User Manual 95 / 284
9.7 dce_http_server
What: dce over http inspection - proxy to/from server
Type: inspector
Usage: inspect
Peg counts:
•dce_http_server.http_server_sessions: successful http server sessions (sum)
•dce_http_server.http_server_session_failures: failed http server sessions (sum)
9.8 dce_smb
What: dce over smb inspection
Type: inspector
Usage: inspect
Configuration:
• bool dce_smb.disable_defrag = false: Disable DCE/RPC defragmentation
• int dce_smb.max_frag_len = 65535: Maximum fragment size for defragmentation { 1514:65535 }
• int dce_smb.reassemble_threshold = 0: Minimum bytes received before performing reassembly { 0:65535 }
• enum dce_smb.smb_fingerprint_policy = none: Target based SMB policy to use { none | client | server | both }
• enum dce_smb.policy = WinXP: Target based policy to use { Win2000 | WinXP | WinVista | Win2003 | Win2008 | Win7 |
Samba | Samba-3.0.37 | Samba-3.0.22 | Samba-3.0.20 }
• int dce_smb.smb_max_chain = 3: SMB max chain size { 0:255 }
• int dce_smb.smb_max_compound = 3: SMB max compound size { 0:255 }
• multi dce_smb.valid_smb_versions = all: Valid SMB versions { v1 | v2 | all }
• enum dce_smb.smb_file_inspection = off: SMB file inspection { off | on | only }
• int dce_smb.smb_file_depth = 16384: SMB file depth for file data { -1: }
• string dce_smb.smb_invalid_shares: SMB shares to alert on
• bool dce_smb.smb_legacy_mode = false: inspect only SMBv1
Rules:
•133:2 (dce_smb) SMB - bad NetBIOS session service session type
•133:3 (dce_smb) SMB - bad SMB message type
•133:4 (dce_smb) SMB - bad SMB Id (not \xffSMB for SMB1 or not \xfeSMB for SMB2)
•133:5 (dce_smb) SMB - bad word count or structure size
•133:6 (dce_smb) SMB - bad byte count
•133:7 (dce_smb) SMB - bad format type
•133:8 (dce_smb) SMB - bad offset
Snort 3 User Manual 96 / 284
•133:9 (dce_smb) SMB - zero total data count
•133:10 (dce_smb) SMB - NetBIOS data length less than SMB header length
•133:12 (dce_smb) SMB - remaining NetBIOS data length less than command byte count
•133:13 (dce_smb) SMB - remaining NetBIOS data length less than command data size
•133:14 (dce_smb) SMB - remaining total data count less than this command data size
•133:15 (dce_smb) SMB - total data sent (STDu64) greater than command total data expected
•133:16 (dce_smb) SMB - byte count less than command data size (STDu64)
•133:17 (dce_smb) SMB - invalid command data size for byte count
•133:18 (dce_smb) SMB - excessive tree connect requests with pending tree connect responses
•133:19 (dce_smb) SMB - excessive read requests with pending read responses
•133:20 (dce_smb) SMB - excessive command chaining
•133:21 (dce_smb) SMB - multiple chained tree connect requests
•133:22 (dce_smb) SMB - multiple chained tree connect requests
•133:23 (dce_smb) SMB - chained/compounded login followed by logoff
•133:24 (dce_smb) SMB - chained/compounded tree connect followed by tree disconnect
•133:25 (dce_smb) SMB - chained/compounded open pipe followed by close pipe
•133:26 (dce_smb) SMB - invalid share access
•133:44 (dce_smb) SMB - invalid SMB version 1 seen
•133:45 (dce_smb) SMB - invalid SMB version 2 seen
•133:46 (dce_smb) SMB - invalid user, tree connect, file binding
•133:47 (dce_smb) SMB - excessive command compounding
•133:48 (dce_smb) SMB - zero data count
•133:50 (dce_smb) SMB - maximum number of outstanding requests exceeded
•133:51 (dce_smb) SMB - outstanding requests with same MID
•133:52 (dce_smb) SMB - deprecated dialect negotiated
•133:53 (dce_smb) SMB - deprecated command used
•133:54 (dce_smb) SMB - unusual command used
•133:55 (dce_smb) SMB - invalid setup count for command
•133:56 (dce_smb) SMB - client attempted multiple dialect negotiations on session
•133:57 (dce_smb) SMB - client attempted to create or set a file’s attributes to readonly/hidden/system
•133:58 (dce_smb) SMB - file offset provided is greater than file size specified
•133:59 (dce_smb) SMB - next command specified in SMB2 header is beyond payload boundary
Peg counts:
•dce_smb.events: total events (sum)
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•dce_smb.pdus: total connection-oriented PDUs (sum)
•dce_smb.binds: total connection-oriented binds (sum)
•dce_smb.bind_acks: total connection-oriented binds acks (sum)
•dce_smb.alter_contexts: total connection-oriented alter contexts (sum)
•dce_smb.alter_context_responses: total connection-oriented alter context responses (sum)
•dce_smb.bind_naks: total connection-oriented bind naks (sum)
•dce_smb.requests: total connection-oriented requests (sum)
•dce_smb.responses: total connection-oriented responses (sum)
•dce_smb.cancels: total connection-oriented cancels (sum)
•dce_smb.orphaned: total connection-oriented orphaned (sum)
•dce_smb.faults: total connection-oriented faults (sum)
•dce_smb.auth3s: total connection-oriented auth3s (sum)
•dce_smb.shutdowns: total connection-oriented shutdowns (sum)
•dce_smb.rejects: total connection-oriented rejects (sum)
•dce_smb.ms_rpc_http_pdus: total connection-oriented MS requests to send RPC over HTTP (sum)
•dce_smb.other_requests: total connection-oriented other requests (sum)
•dce_smb.other_responses: total connection-oriented other responses (sum)
•dce_smb.request_fragments: total connection-oriented request fragments (sum)
•dce_smb.response_fragments: total connection-oriented response fragments (sum)
•dce_smb.client_max_fragment_size: connection-oriented client maximum fragment size (sum)
•dce_smb.client_min_fragment_size: connection-oriented client minimum fragment size (sum)
•dce_smb.client_segs_reassembled: total connection-oriented client segments reassembled (sum)
•dce_smb.client_frags_reassembled: total connection-oriented client fragments reassembled (sum)
•dce_smb.server_max_fragment_size: connection-oriented server maximum fragment size (sum)
•dce_smb.server_min_fragment_size: connection-oriented server minimum fragment size (sum)
•dce_smb.server_segs_reassembled: total connection-oriented server segments reassembled (sum)
•dce_smb.server_frags_reassembled: total connection-oriented server fragments reassembled (sum)
•dce_smb.sessions: total smb sessions (sum)
•dce_smb.packets: total smb packets (sum)
•dce_smb.ignored_bytes: total ignored bytes (sum)
•dce_smb.smb_client_segs_reassembled: total smb client segments reassembled (sum)
•dce_smb.smb_server_segs_reassembled: total smb server segments reassembled (sum)
•dce_smb.max_outstanding_requests: total smb maximum outstanding requests (sum)
•dce_smb.files_processed: total smb files processed (sum)
•dce_smb.smbv2_create: total number of SMBv2 create packets seen (sum)
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•dce_smb.smbv2_write: total number of SMBv2 write packets seen (sum)
•dce_smb.smbv2_read: total number of SMBv2 read packets seen (sum)
•dce_smb.smbv2_set_info: total number of SMBv2 set info packets seen (sum)
•dce_smb.smbv2_tree_connect: total number of SMBv2 tree connect packets seen (sum)
•dce_smb.smbv2_tree_disconnect: total number of SMBv2 tree disconnect packets seen (sum)
•dce_smb.smbv2_close: total number of SMBv2 close packets seen (sum)
•dce_smb.concurrent_sessions: total concurrent sessions (now)
•dce_smb.max_concurrent_sessions: maximum concurrent sessions (max)
9.9 dce_tcp
What: dce over tcp inspection
Type: inspector
Usage: inspect
Configuration:
• bool dce_tcp.disable_defrag = false: Disable DCE/RPC defragmentation
• int dce_tcp.max_frag_len = 65535: Maximum fragment size for defragmentation { 1514:65535 }
• int dce_tcp.reassemble_threshold = 0: Minimum bytes received before performing reassembly { 0:65535 }
• enum dce_tcp.policy = WinXP: Target based policy to use { Win2000 | WinXP | WinVista | Win2003 | Win2008 | Win7 |
Samba | Samba-3.0.37 | Samba-3.0.22 | Samba-3.0.20 }
Rules:
•133:27 (dce_tcp) connection oriented DCE/RPC - invalid major version
•133:28 (dce_tcp) connection oriented DCE/RPC - invalid minor version
•133:29 (dce_tcp) connection-oriented DCE/RPC - invalid PDU type
•133:30 (dce_tcp) connection-oriented DCE/RPC - fragment length less than header size
•133:32 (dce_tcp) connection-oriented DCE/RPC - no context items specified
•133:33 (dce_tcp) connection-oriented DCE/RPC -no transfer syntaxes specified
•133:34 (dce_tcp) connection-oriented DCE/RPC - fragment length on non-last fragment less than maximum negotiated frag-
ment transmit size for client
•133:35 (dce_tcp) connection-oriented DCE/RPC - fragment length greater than maximum negotiated fragment transmit size
•133:36 (dce_tcp) connection-oriented DCE/RPC - alter context byte order different from bind
•133:37 (dce_tcp) connection-oriented DCE/RPC - call id of non first/last fragment different from call id established for frag-
mented request
•133:38 (dce_tcp) connection-oriented DCE/RPC - opnum of non first/last fragment different from opnum established for
fragmented request
•133:39 (dce_tcp) connection-oriented DCE/RPC - context id of non first/last fragment different from context id established for
fragmented request
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Peg counts:
•dce_tcp.events: total events (sum)
•dce_tcp.pdus: total connection-oriented PDUs (sum)
•dce_tcp.binds: total connection-oriented binds (sum)
•dce_tcp.bind_acks: total connection-oriented binds acks (sum)
•dce_tcp.alter_contexts: total connection-oriented alter contexts (sum)
•dce_tcp.alter_context_responses: total connection-oriented alter context responses (sum)
•dce_tcp.bind_naks: total connection-oriented bind naks (sum)
•dce_tcp.requests: total connection-oriented requests (sum)
•dce_tcp.responses: total connection-oriented responses (sum)
•dce_tcp.cancels: total connection-oriented cancels (sum)
•dce_tcp.orphaned: total connection-oriented orphaned (sum)
•dce_tcp.faults: total connection-oriented faults (sum)
•dce_tcp.auth3s: total connection-oriented auth3s (sum)
•dce_tcp.shutdowns: total connection-oriented shutdowns (sum)
•dce_tcp.rejects: total connection-oriented rejects (sum)
•dce_tcp.ms_rpc_http_pdus: total connection-oriented MS requests to send RPC over HTTP (sum)
•dce_tcp.other_requests: total connection-oriented other requests (sum)
•dce_tcp.other_responses: total connection-oriented other responses (sum)
•dce_tcp.request_fragments: total connection-oriented request fragments (sum)
•dce_tcp.response_fragments: total connection-oriented response fragments (sum)
•dce_tcp.client_max_fragment_size: connection-oriented client maximum fragment size (sum)
•dce_tcp.client_min_fragment_size: connection-oriented client minimum fragment size (sum)
•dce_tcp.client_segs_reassembled: total connection-oriented client segments reassembled (sum)
•dce_tcp.client_frags_reassembled: total connection-oriented client fragments reassembled (sum)
•dce_tcp.server_max_fragment_size: connection-oriented server maximum fragment size (sum)
•dce_tcp.server_min_fragment_size: connection-oriented server minimum fragment size (sum)
•dce_tcp.server_segs_reassembled: total connection-oriented server segments reassembled (sum)
•dce_tcp.server_frags_reassembled: total connection-oriented server fragments reassembled (sum)
•dce_tcp.tcp_sessions: total tcp sessions (sum)
•dce_tcp.tcp_packets: total tcp packets (sum)
•dce_tcp.concurrent_sessions: total concurrent sessions (now)
•dce_tcp.max_concurrent_sessions: maximum concurrent sessions (max)
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9.10 dce_udp
What: dce over udp inspection
Type: inspector
Usage: inspect
Configuration:
• bool dce_udp.disable_defrag = false: Disable DCE/RPC defragmentation
• int dce_udp.max_frag_len = 65535: Maximum fragment size for defragmentation { 1514:65535 }
Rules:
•133:40 (dce_udp) connection-less DCE/RPC - invalid major version
•133:41 (dce_udp) connection-less DCE/RPC - invalid PDU type
•133:42 (dce_udp) connection-less DCE/RPC - data length less than header size
•133:43 (dce_udp) connection-less DCE/RPC - bad sequence number
Peg counts:
•dce_udp.events: total events (sum)
•dce_udp.udp_sessions: total udp sessions (sum)
•dce_udp.udp_packets: total udp packets (sum)
•dce_udp.requests: total connection-less requests (sum)
•dce_udp.acks: total connection-less acks (sum)
•dce_udp.cancels: total connection-less cancels (sum)
•dce_udp.client_facks: total connection-less client facks (sum)
•dce_udp.ping: total connection-less ping (sum)
•dce_udp.responses: total connection-less responses (sum)
•dce_udp.rejects: total connection-less rejects (sum)
•dce_udp.cancel_acks: total connection-less cancel acks (sum)
•dce_udp.server_facks: total connection-less server facks (sum)
•dce_udp.faults: total connection-less faults (sum)
•dce_udp.no_calls: total connection-less no calls (sum)
•dce_udp.working: total connection-less working (sum)
•dce_udp.other_requests: total connection-less other requests (sum)
•dce_udp.other_responses: total connection-less other responses (sum)
•dce_udp.fragments: total connection-less fragments (sum)
•dce_udp.max_fragment_size: connection-less maximum fragment size (sum)
•dce_udp.frags_reassembled: total connection-less fragments reassembled (sum)
•dce_udp.max_seqnum: max connection-less seqnum (sum)
•dce_udp.concurrent_sessions: total concurrent sessions (now)
•dce_udp.max_concurrent_sessions: maximum concurrent sessions (max)
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9.11 dnp3
What: dnp3 inspection
Type: inspector
Usage: inspect
Configuration:
• bool dnp3.check_crc = false: validate checksums in DNP3 link layer frames
Rules:
•145:1 (dnp3) DNP3 link-layer frame contains bad CRC
•145:2 (dnp3) DNP3 link-layer frame was dropped
•145:3 (dnp3) DNP3 transport-layer segment was dropped during reassembly
•145:4 (dnp3) DNP3 reassembly buffer was cleared without reassembling a complete message
•145:5 (dnp3) DNP3 link-layer frame uses a reserved address
•145:6 (dnp3) DNP3 application-layer fragment uses a reserved function code
Peg counts:
•dnp3.total_packets: total packets (sum)
•dnp3.udp_packets: total udp packets (sum)
•dnp3.tcp_pdus: total tcp pdus (sum)
•dnp3.dnp3_link_layer_frames: total dnp3 link layer frames (sum)
•dnp3.dnp3_application_pdus: total dnp3 application pdus (sum)
•dnp3.concurrent_sessions: total concurrent dnp3 sessions (now)
•dnp3.max_concurrent_sessions: maximum concurrent dnp3 sessions (max)
9.12 dns
What: dns inspection
Type: inspector
Usage: inspect
Rules:
•131:1 (dns) obsolete DNS RR types
•131:2 (dns) experimental DNS RR types
•131:3 (dns) DNS client rdata txt overflow
Peg counts:
•dns.packets: total packets processed (sum)
•dns.requests: total dns requests (sum)
•dns.responses: total dns responses (sum)
•dns.concurrent_sessions: total concurrent dns sessions (now)
•dns.max_concurrent_sessions: maximum concurrent dns sessions (max)
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9.13 dpx
What: dynamic inspector example
Type: inspector
Usage: inspect
Configuration:
• port dpx.port: port to check
• int dpx.max = 0: maximum payload before alert { 0:65535 }
Rules:
•256:1 (dpx) too much data sent to port
Peg counts:
•dpx.packets: total packets (sum)
9.14 file_id
What: configure file identification
Type: inspector
Usage: global
Configuration:
• int file_id.type_depth = 1460: stop type ID at this point { 0: }
• int file_id.signature_depth = 10485760: stop signature at this point { 0: }
• int file_id.block_timeout = 86400: stop blocking after this many seconds { 0: }
• int file_id.lookup_timeout = 2: give up on lookup after this many seconds { 0: }
• bool file_id.block_timeout_lookup = false: block if lookup times out
• int file_id.capture_memcap = 100: memcap for file capture in megabytes { 0: }
• int file_id.capture_max_size = 1048576: stop file capture beyond this point { 0: }
• int file_id.capture_min_size = 0: stop file capture if file size less than this { 0: }
• int file_id.capture_block_size = 32768: file capture block size in bytes { 8: }
• int file_id.max_files_cached = 65536: maximal number of files cached in memory { 8: }
• bool file_id.enable_type = true: enable type ID
• bool file_id.enable_signature = true: enable signature calculation
• bool file_id.enable_capture = false: enable file capture
• int file_id.show_data_depth = 100: print this many octets { 0: }
• int file_id.file_rules[].rev = 0: rule revision { 0: }
• string file_id.file_rules[].msg: information about the file type
• string file_id.file_rules[].type: file type name
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• int file_id.file_rules[].id = 0: file type id { 0: }
• string file_id.file_rules[].category: file type category
• string file_id.file_rules[].group: comma separated list of groups associated with file type
• string file_id.file_rules[].version: file type version
• string file_id.file_rules[].magic[].content: file magic content
• int file_id.file_rules[].magic[].offset = 0: file magic offset { 0: }
• int file_id.file_policy[].when.file_type_id = 0: unique ID for file type in file magic rule { 0: }
• string file_id.file_policy[].when.sha256: SHA 256
• enum file_id.file_policy[].use.verdict = unknown: what to do with matching traffic { unknown | log | stop | block | reset }
• bool file_id.file_policy[].use.enable_file_type = false: true/false →enable/disable file type identification
• bool file_id.file_policy[].use.enable_file_signature = false: true/false →enable/disable file signature
• bool file_id.file_policy[].use.enable_file_capture = false: true/false →enable/disable file capture
• bool file_id.trace_type = false: enable runtime dump of type info
• bool file_id.trace_signature = false: enable runtime dump of signature info
• bool file_id.trace_stream = false: enable runtime dump of file data
• int file_id.verdict_delay = 0: number of queries to return final verdict { 0: }
Peg counts:
•file_id.total_files: number of files processed (sum)
•file_id.total_file_data: number of file data bytes processed (sum)
•file_id.cache_failures: number of file cache add failures (sum)
9.15 file_log
What: log file event to file.log
Type: inspector
Usage: inspect
Configuration:
• bool file_log.log_pkt_time = true: log the packet time when event generated
• bool file_log.log_sys_time = false: log the system time when event generated
Peg counts:
•file_log.total_events: total file events (sum)
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9.16 ftp_client
What: FTP client configuration module for use with ftp_server
Type: inspector
Usage: inspect
Configuration:
• bool ftp_client.bounce = false: check for bounces
• addr ftp_client.bounce_to[].address = 1.0.0.0/32: allowed IP address in CIDR format
• port ftp_client.bounce_to[].port = 20: allowed port { 1: }
• port ftp_client.bounce_to[].last_port: optional allowed range from port to last_port inclusive { 0: }
• bool ftp_client.ignore_telnet_erase_cmds = false: ignore erase character and erase line commands when normalizing
• int ftp_client.max_resp_len = -1: maximum FTP response accepted by client { -1: }
• bool ftp_client.telnet_cmds = false: detect Telnet escape sequences on FTP control channel
9.17 ftp_data
What: FTP data channel handler
Type: inspector
Usage: inspect
Peg counts:
•ftp_data.packets: total packets (sum)
9.18 ftp_server
What: main FTP module; ftp_client should also be configured
Type: inspector
Usage: inspect
Configuration:
• string ftp_server.chk_str_fmt: check the formatting of the given commands
• string ftp_server.data_chan_cmds: check the formatting of the given commands
• string ftp_server.data_rest_cmds: check the formatting of the given commands
• string ftp_server.data_xfer_cmds: check the formatting of the given commands
• string ftp_server.directory_cmds[].dir_cmd: directory command
• int ftp_server.directory_cmds[].rsp_code = 200: expected successful response code for command { 200: }
• string ftp_server.file_put_cmds: check the formatting of the given commands
• string ftp_server.file_get_cmds: check the formatting of the given commands
• string ftp_server.encr_cmds: check the formatting of the given commands
• string ftp_server.login_cmds: check the formatting of the given commands
Snort 3 User Manual 105 / 284
• bool ftp_server.check_encrypted = false: check for end of encryption
• string ftp_server.cmd_validity[].command: command string
• string ftp_server.cmd_validity[].format: format specification
• int ftp_server.cmd_validity[].length = 0: specify non-default maximum for command { 0: }
• int ftp_server.def_max_param_len = 100: default maximum length of commands handled by server; 0 is unlimited { 1: }
• bool ftp_server.encrypted_traffic = false: check for encrypted Telnet and FTP
• string ftp_server.ftp_cmds: specify additional commands supported by server beyond RFC 959
• bool ftp_server.ignore_data_chan = false: do not inspect FTP data channels
• bool ftp_server.ignore_telnet_erase_cmds = false: ignore erase character and erase line commands when normalizing
• bool ftp_server.print_cmds = false: print command configurations on start up
• bool ftp_server.telnet_cmds = false: detect Telnet escape sequences of FTP control channel
Rules:
•125:1 (ftp_server) TELNET cmd on FTP command channel
•125:2 (ftp_server) invalid FTP command
•125:3 (ftp_server) FTP command parameters were too long
•125:4 (ftp_server) FTP command parameters were malformed
•125:5 (ftp_server) FTP command parameters contained potential string format
•125:6 (ftp_server) FTP response message was too long
•125:7 (ftp_server) FTP traffic encrypted
•125:8 (ftp_server) FTP bounce attempt
•125:9 (ftp_server) evasive (incomplete) TELNET cmd on FTP command channel
Peg counts:
•ftp_server.total_packets: total packets (sum)
•ftp_server.concurrent_sessions: total concurrent FTP sessions (now)
•ftp_server.max_concurrent_sessions: maximum concurrent FTP sessions (max)
9.19 gtp_inspect
What: gtp control channel inspection
Type: inspector
Usage: inspect
Configuration:
• int gtp_inspect[].version = 2: GTP version { 0:2 }
• int gtp_inspect[].messages[].type = 0: message type code { 0:255 }
• string gtp_inspect[].messages[].name: message name
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• int gtp_inspect[].infos[].type = 0: information element type code { 0:255 }
• string gtp_inspect[].infos[].name: information element name
• int gtp_inspect[].infos[].length = 0: information element type code { 0:255 }
Rules:
•143:1 (gtp_inspect) message length is invalid
•143:2 (gtp_inspect) information element length is invalid
•143:3 (gtp_inspect) information elements are out of order
Peg counts:
•gtp_inspect.sessions: total sessions processed (sum)
•gtp_inspect.concurrent_sessions: total concurrent gtp sessions (now)
•gtp_inspect.max_concurrent_sessions: maximum concurrent gtp sessions (max)
•gtp_inspect.events: requests (sum)
•gtp_inspect.unknown_types: unknown message types (sum)
•gtp_inspect.unknown_infos: unknown information elements (sum)
9.20 http_inspect
What: HTTP inspector
Type: inspector
Usage: inspect
Configuration:
• int http_inspect.request_depth = -1: maximum request message body bytes to examine (-1 no limit) { -1: }
• int http_inspect.response_depth = -1: maximum response message body bytes to examine (-1 no limit) { -1: }
• bool http_inspect.unzip = true: decompress gzip and deflate message bodies
• bool http_inspect.normalize_utf = true: normalize charset utf encodings in response bodies
• bool http_inspect.decompress_pdf = false: decompress pdf files in response bodies
• bool http_inspect.decompress_swf = false: decompress swf files in response bodies
• bool http_inspect.normalize_javascript = false: normalize javascript in response bodies
• int http_inspect.max_javascript_whitespaces = 200: maximum consecutive whitespaces allowed within the Javascript ob-
fuscated data { 1:65535 }
• bit_list http_inspect.bad_characters: alert when any of specified bytes are present in URI after percent decoding { 255 }
• string http_inspect.ignore_unreserved: do not alert when the specified unreserved characters are percent-encoded in a
URI.Unreserved characters are 0-9, a-z, A-Z, period, underscore, tilde, and minus. { (optional) }
• bool http_inspect.percent_u = false: normalize %uNNNN and %UNNNN encodings
• bool http_inspect.utf8 = true: normalize 2-byte and 3-byte UTF-8 characters to a single byte
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• bool http_inspect.utf8_bare_byte = false: when doing UTF-8 character normalization include bytes that were not percent
encoded
• bool http_inspect.iis_unicode = false: use IIS unicode code point mapping to normalize characters
• string http_inspect.iis_unicode_map_file: file containing code points for IIS unicode. { (optional) }
• int http_inspect.iis_unicode_code_page = 1252: code page to use from the IIS unicode map file { 0:65535 }
• bool http_inspect.iis_double_decode = false: perform double decoding of percent encodings to normalize characters
• int http_inspect.oversize_dir_length = 300: maximum length for URL directory { 1:65535 }
• bool http_inspect.backslash_to_slash = false: replace \ with / when normalizing URIs
• bool http_inspect.plus_to_space = true: replace + with <sp> when normalizing URIs
• bool http_inspect.simplify_path = true: reduce URI directory path to simplest form
• bool http_inspect.test_input = false: read HTTP messages from text file
• bool http_inspect.test_output = false: print out HTTP section data
• int http_inspect.print_amount = 1200: number of characters to print from a Field { 1:1000000 }
• bool http_inspect.print_hex = false: nonprinting characters printed in [HH] format instead of using an asterisk
• bool http_inspect.show_pegs = true: display peg counts with test output
• bool http_inspect.show_scan = false: display scanned segments
Rules:
•119:1 (http_inspect) ascii encoding
•119:2 (http_inspect) double decoding attack
•119:3 (http_inspect) u encoding
•119:4 (http_inspect) bare byte unicode encoding
•119:5 (http_inspect) obsolete event—deleted
•119:6 (http_inspect) UTF-8 encoding
•119:7 (http_inspect) unicode map code point encoding in URI
•119:8 (http_inspect) multi_slash encoding
•119:9 (http_inspect) backslash used in URI path
•119:10 (http_inspect) self directory traversal
•119:11 (http_inspect) directory traversal
•119:12 (http_inspect) apache whitespace (tab)
•119:13 (http_inspect) HTTP header line terminated by LF without a CR
•119:14 (http_inspect) non-RFC defined char
•119:15 (http_inspect) oversize request-uri directory
•119:16 (http_inspect) oversize chunk encoding
•119:17 (http_inspect) unauthorized proxy use detected
•119:18 (http_inspect) webroot directory traversal
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•119:19 (http_inspect) long header
•119:20 (http_inspect) max header fields
•119:21 (http_inspect) multiple content length
•119:22 (http_inspect) obsolete event—deleted
•119:23 (http_inspect) invalid IP in true-client-IP/XFF header
•119:24 (http_inspect) multiple host hdrs detected
•119:25 (http_inspect) hostname exceeds 255 characters
•119:26 (http_inspect) too much whitespace in header (not implemented yet)
•119:27 (http_inspect) client consecutive small chunk sizes
•119:28 (http_inspect) POST or PUT w/o content-length or chunks
•119:29 (http_inspect) multiple true ips in a session
•119:30 (http_inspect) both true-client-IP and XFF hdrs present
•119:31 (http_inspect) unknown method
•119:32 (http_inspect) simple request
•119:33 (http_inspect) unescaped space in HTTP URI
•119:34 (http_inspect) too many pipelined requests
•119:35 (http_inspect) anomalous http server on undefined HTTP port
•119:36 (http_inspect) invalid status code in HTTP response
•119:37 (http_inspect) unused event number—should not appear
•119:38 (http_inspect) HTTP response has UTF charset that failed to normalize
•119:39 (http_inspect) HTTP response has UTF-7 charset
•119:40 (http_inspect) HTTP response gzip decompression failed
•119:41 (http_inspect) server consecutive small chunk sizes
•119:42 (http_inspect) unused event number—should not appear
•119:43 (http_inspect) javascript obfuscation levels exceeds 1
•119:44 (http_inspect) javascript whitespaces exceeds max allowed
•119:45 (http_inspect) multiple encodings within javascript obfuscated data
•119:46 (http_inspect) SWF file zlib decompression failure
•119:47 (http_inspect) SWF file LZMA decompression failure
•119:48 (http_inspect) PDF file deflate decompression failure
•119:49 (http_inspect) PDF file unsupported compression type
•119:50 (http_inspect) PDF file cascaded compression
•119:51 (http_inspect) PDF file parse failure
•119:52 (http_inspect) not HTTP traffic
•119:53 (http_inspect) chunk length has excessive leading zeros
Snort 3 User Manual 109 / 284
•119:54 (http_inspect) white space before or between messages
•119:55 (http_inspect) request message without URI
•119:56 (http_inspect) control character in reason phrase
•119:57 (http_inspect) illegal extra whitespace in start line
•119:58 (http_inspect) corrupted HTTP version
•119:59 (http_inspect) unknown HTTP version
•119:60 (http_inspect) format error in HTTP header
•119:61 (http_inspect) chunk header options present
•119:62 (http_inspect) URI badly formatted
•119:63 (http_inspect) unrecognized type of percent encoding in URI
•119:64 (http_inspect) HTTP chunk misformatted
•119:65 (http_inspect) white space following chunk length
•119:66 (http_inspect) white space within header name
•119:67 (http_inspect) excessive gzip compression
•119:68 (http_inspect) gzip decompression failed
•119:69 (http_inspect) HTTP 0.9 requested followed by another request
•119:70 (http_inspect) HTTP 0.9 request following a normal request
•119:71 (http_inspect) message has both Content-Length and Transfer-Encoding
•119:72 (http_inspect) status code implying no body combined with Transfer-Encoding or nonzero Content-Length
•119:73 (http_inspect) Transfer-Encoding not ending with chunked
•119:74 (http_inspect) Transfer-Encoding with encodings before chunked
•119:75 (http_inspect) misformatted HTTP traffic
•119:76 (http_inspect) unsupported Content-Encoding used
•119:77 (http_inspect) unknown Content-Encoding used
•119:78 (http_inspect) multiple Content-Encodings applied
•119:79 (http_inspect) server response before client request
•119:80 (http_inspect) PDF/SWF decompression of server response too big
•119:81 (http_inspect) nonprinting character in HTTP message header name
•119:82 (http_inspect) bad Content-Length value in HTTP header
•119:83 (http_inspect) HTTP header line wrapped
•119:84 (http_inspect) HTTP header line terminated by CR without a LF
•119:85 (http_inspect) chunk terminated by nonstandard separator
•119:86 (http_inspect) chunk length terminated by LF without CR
•119:87 (http_inspect) more than one response with 100 status code
•119:88 (http_inspect) 100 status code not in response to Expect header
Snort 3 User Manual 110 / 284
•119:89 (http_inspect) 1XX status code other than 100 or 101
•119:90 (http_inspect) Expect header sent without a message body
•119:91 (http_inspect) HTTP 1.0 message with Transfer-Encoding header
•119:92 (http_inspect) Content-Transfer-Encoding used as HTTP header
•119:93 (http_inspect) illegal field in chunked message trailers
•119:94 (http_inspect) header field inappropriately appears twice or has two values
•119:95 (http_inspect) invalid value chunked in Content-Encoding header
•119:96 (http_inspect) 206 response sent to a request without a Range header
•119:97 (http_inspect) HTTP in version field not all upper case
Peg counts:
•http_inspect.flows: HTTP connections inspected (sum)
•http_inspect.scans: TCP segments scanned looking for HTTP messages (sum)
•http_inspect.reassembles: TCP segments combined into HTTP messages (sum)
•http_inspect.inspections: total message sections inspected (sum)
•http_inspect.requests: HTTP request messages inspected (sum)
•http_inspect.responses: HTTP response messages inspected (sum)
•http_inspect.get_requests: GET requests inspected (sum)
•http_inspect.head_requests: HEAD requests inspected (sum)
•http_inspect.post_requests: POST requests inspected (sum)
•http_inspect.put_requests: PUT requests inspected (sum)
•http_inspect.delete_requests: DELETE requests inspected (sum)
•http_inspect.connect_requests: CONNECT requests inspected (sum)
•http_inspect.options_requests: OPTIONS requests inspected (sum)
•http_inspect.trace_requests: TRACE requests inspected (sum)
•http_inspect.other_requests: other request methods inspected (sum)
•http_inspect.request_bodies: POST, PUT, and other requests with message bodies (sum)
•http_inspect.chunked: chunked message bodies (sum)
•http_inspect.uri_normalizations: URIs needing to be normalization (sum)
•http_inspect.uri_path: URIs with path problems (sum)
•http_inspect.uri_coding: URIs with character coding problems (sum)
•http_inspect.concurrent_sessions: total concurrent http sessions (now)
•http_inspect.max_concurrent_sessions: maximum concurrent http sessions (max)
Snort 3 User Manual 111 / 284
9.21 imap
What: imap inspection
Type: inspector
Usage: inspect
Configuration:
• int imap.b64_decode_depth = 1460: base64 decoding depth { -1:65535 }
• int imap.bitenc_decode_depth = 1460: non-Encoded MIME attachment extraction depth { -1:65535 }
• int imap.qp_decode_depth = 1460: quoted Printable decoding depth { -1:65535 }
• int imap.uu_decode_depth = 1460: Unix-to-Unix decoding depth { -1:65535 }
Rules:
•141:1 (imap) unknown IMAP3 command
•141:2 (imap) unknown IMAP3 response
•141:4 (imap) base64 decoding failed
•141:5 (imap) quoted-printable decoding failed
•141:7 (imap) Unix-to-Unix decoding failed
Peg counts:
•imap.packets: total packets processed (sum)
•imap.sessions: total imap sessions (sum)
•imap.concurrent_sessions: total concurrent imap sessions (now)
•imap.max_concurrent_sessions: maximum concurrent imap sessions (max)
•imap.b64_attachments: total base64 attachments decoded (sum)
•imap.b64_decoded_bytes: total base64 decoded bytes (sum)
•imap.qp_attachments: total quoted-printable attachments decoded (sum)
•imap.qp_decoded_bytes: total quoted-printable decoded bytes (sum)
•imap.uu_attachments: total uu attachments decoded (sum)
•imap.uu_decoded_bytes: total uu decoded bytes (sum)
•imap.non_encoded_attachments: total non-encoded attachments extracted (sum)
•imap.non_encoded_bytes: total non-encoded extracted bytes (sum)
Snort 3 User Manual 112 / 284
9.22 modbus
What: modbus inspection
Type: inspector
Usage: inspect
Rules:
•144:1 (modbus) length in Modbus MBAP header does not match the length needed for the given function
•144:2 (modbus) Modbus protocol ID is non-zero
•144:3 (modbus) reserved Modbus function code in use
Peg counts:
•modbus.sessions: total sessions processed (sum)
•modbus.frames: total Modbus messages (sum)
•modbus.concurrent_sessions: total concurrent modbus sessions (now)
•modbus.max_concurrent_sessions: maximum concurrent modbus sessions (max)
9.23 normalizer
What: packet scrubbing for inline mode
Type: inspector
Usage: inspect
Configuration:
• bool normalizer.ip4.base = true: clear options
• bool normalizer.ip4.df = false: clear don’t frag flag
• bool normalizer.ip4.rf = false: clear reserved flag
• bool normalizer.ip4.tos = false: clear tos / differentiated services byte
• bool normalizer.ip4.trim = false: truncate excess payload beyond datagram length
• bool normalizer.tcp.base = true: clear reserved bits and option padding and fix urgent pointer / flags issues
• bool normalizer.tcp.block = true: allow packet drops during TCP normalization
• bool normalizer.tcp.urp = true: adjust urgent pointer if beyond segment length
• bool normalizer.tcp.ips = false: ensure consistency in retransmitted data
• select normalizer.tcp.ecn = off: clear ecn for all packets | sessions w/o ecn setup { off | packet | stream }
• bool normalizer.tcp.pad = true: clear any option padding bytes
• bool normalizer.tcp.trim_syn = false: remove data on SYN
• bool normalizer.tcp.trim_rst = false: remove any data from RST packet
• bool normalizer.tcp.trim_win = false: trim data to window
• bool normalizer.tcp.trim_mss = false: trim data to MSS
Snort 3 User Manual 113 / 284
• bool normalizer.tcp.trim = false: enable all of the TCP trim options
• bool normalizer.tcp.opts = true: clear all options except mss, wscale, timestamp, and any explicitly allowed
• bool normalizer.tcp.req_urg = true: clear the urgent pointer if the urgent flag is not set
• bool normalizer.tcp.req_pay = true: clear the urgent pointer and the urgent flag if there is no payload
• bool normalizer.tcp.rsv = true: clear the reserved bits in the TCP header
• bool normalizer.tcp.req_urp = true: clear the urgent flag if the urgent pointer is not set
• multi normalizer.tcp.allow_names: don’t clear given option names { sack | echo | partial_order | conn_count | alt_checksum |
md5 }
• string normalizer.tcp.allow_codes: don’t clear given option codes
• bool normalizer.ip6 = false: clear reserved flag
• bool normalizer.icmp4 = false: clear reserved flag
• bool normalizer.icmp6 = false: clear reserved flag
Peg counts:
•normalizer.test_ip4_trim: test eth packets trimmed to datagram size (sum)
•normalizer.ip4_trim: eth packets trimmed to datagram size (sum)
•normalizer.test_ip4_tos: test type of service normalizations (sum)
•normalizer.ip4_tos: type of service normalizations (sum)
•normalizer.test_ip4_df: test don’t frag bit normalizations (sum)
•normalizer.ip4_df: don’t frag bit normalizations (sum)
•normalizer.test_ip4_rf: test reserved flag bit clears (sum)
•normalizer.ip4_rf: reserved flag bit clears (sum)
•normalizer.test_ip4_ttl: test time-to-live normalizations (sum)
•normalizer.ip4_ttl: time-to-live normalizations (sum)
•normalizer.test_ip4_opts: test ip4 options cleared (sum)
•normalizer.ip4_opts: ip4 options cleared (sum)
•normalizer.test_icmp4_echo: test icmp4 ping normalizations (sum)
•normalizer.icmp4_echo: icmp4 ping normalizations (sum)
•normalizer.test_ip6_hops: test ip6 hop limit normalizations (sum)
•normalizer.ip6_hops: ip6 hop limit normalizations (sum)
•normalizer.test_ip6_options: test ip6 options cleared (sum)
•normalizer.ip6_options: ip6 options cleared (sum)
•normalizer.test_icmp6_echo: test icmp6 echo normalizations (sum)
•normalizer.icmp6_echo: icmp6 echo normalizations (sum)
•normalizer.test_tcp_syn_options: test SYN only options cleared from non-SYN packets (sum)
•normalizer.tcp_syn_options: SYN only options cleared from non-SYN packets (sum)
Snort 3 User Manual 114 / 284
•normalizer.test_tcp_options: test packets with options cleared (sum)
•normalizer.tcp_options: packets with options cleared (sum)
•normalizer.test_tcp_padding: test packets with padding cleared (sum)
•normalizer.tcp_padding: packets with padding cleared (sum)
•normalizer.test_tcp_reserved: test packets with reserved bits cleared (sum)
•normalizer.tcp_reserved: packets with reserved bits cleared (sum)
•normalizer.test_tcp_nonce: test packets with nonce bit cleared (sum)
•normalizer.tcp_nonce: packets with nonce bit cleared (sum)
•normalizer.test_tcp_urgent_ptr: test packets without data with urgent pointer cleared (sum)
•normalizer.tcp_urgent_ptr: packets without data with urgent pointer cleared (sum)
•normalizer.test_tcp_ecn_pkt: test packets with ECN bits cleared (sum)
•normalizer.tcp_ecn_pkt: packets with ECN bits cleared (sum)
•normalizer.test_tcp_ts_ecr: test timestamp cleared on non-ACKs (sum)
•normalizer.tcp_ts_ecr: timestamp cleared on non-ACKs (sum)
•normalizer.test_tcp_req_urg: test cleared urgent pointer when urgent flag is not set (sum)
•normalizer.tcp_req_urg: cleared urgent pointer when urgent flag is not set (sum)
•normalizer.test_tcp_req_pay: test cleared urgent pointer and urgent flag when there is no payload (sum)
•normalizer.tcp_req_pay: cleared urgent pointer and urgent flag when there is no payload (sum)
•normalizer.test_tcp_req_urp: test cleared the urgent flag if the urgent pointer is not set (sum)
•normalizer.tcp_req_urp: cleared the urgent flag if the urgent pointer is not set (sum)
•normalizer.test_tcp_trim_syn: test tcp segments trimmed on SYN (sum)
•normalizer.tcp_trim_syn: tcp segments trimmed on SYN (sum)
•normalizer.test_tcp_trim_rst: test RST packets with data trimmed (sum)
•normalizer.tcp_trim_rst: RST packets with data trimmed (sum)
•normalizer.test_tcp_trim_win: test data trimmed to window (sum)
•normalizer.tcp_trim_win: data trimmed to window (sum)
•normalizer.test_tcp_trim_mss: test data trimmed to MSS (sum)
•normalizer.tcp_trim_mss: data trimmed to MSS (sum)
•normalizer.test_tcp_ecn_session: test ECN bits cleared (sum)
•normalizer.tcp_ecn_session: ECN bits cleared (sum)
•normalizer.test_tcp_ts_nop: test timestamp options cleared (sum)
•normalizer.tcp_ts_nop: timestamp options cleared (sum)
•normalizer.test_tcp_ips_data: test normalized segments (sum)
•normalizer.tcp_ips_data: normalized segments (sum)
•normalizer.test_tcp_block: test blocked segments (sum)
•normalizer.tcp_block: blocked segments (sum)
Snort 3 User Manual 115 / 284
9.24 packet_capture
What: raw packet dumping facility
Type: inspector
Usage: context
Configuration:
• bool packet_capture.enable = false: initially enable packet dumping
• string packet_capture.filter: bpf filter to use for packet dump
Commands:
•packet_capture.enable(filter): dump raw packets
•packet_capture.disable(): stop packet dump
Peg counts:
•packet_capture.processed: packets processed against filter (sum)
•packet_capture.captured: packets matching dumped after matching filter (sum)
9.25 perf_monitor
What: performance monitoring and flow statistics collection
Type: inspector
Usage: context
Configuration:
• bool perf_monitor.base = true: enable base statistics { nullptr }
• bool perf_monitor.cpu = false: enable cpu statistics { nullptr }
• bool perf_monitor.flow = false: enable traffic statistics
• bool perf_monitor.flow_ip = false: enable statistics on host pairs
• int perf_monitor.packets = 10000: minimum packets to report { 0: }
• int perf_monitor.seconds = 60: report interval { 1: }
• int perf_monitor.flow_ip_memcap = 52428800: maximum memory in bytes for flow tracking { 8200: }
• int perf_monitor.max_file_size = 1073741824: files will be rolled over if they exceed this size { 4096: }
• int perf_monitor.flow_ports = 1023: maximum ports to track { 0:65535 }
• enum perf_monitor.output = file: output location for stats { file | console }
• string perf_monitor.modules[].name: name of the module
• string perf_monitor.modules[].pegs: list of statistics to track or empty for all counters
• enum perf_monitor.format = csv: output format for stats { csv | text | json | flatbuffers }
• bool perf_monitor.summary = false: output summary at shutdown
Peg counts:
•perf_monitor.packets: total packets (sum)
Snort 3 User Manual 116 / 284
9.26 pop
What: pop inspection
Type: inspector
Usage: inspect
Configuration:
• int pop.b64_decode_depth = 1460: base64 decoding depth { -1:65535 }
• int pop.bitenc_decode_depth = 1460: Non-Encoded MIME attachment extraction depth { -1:65535 }
• int pop.qp_decode_depth = 1460: Quoted Printable decoding depth { -1:65535 }
• int pop.uu_decode_depth = 1460: Unix-to-Unix decoding depth { -1:65535 }
Rules:
•142:1 (pop) unknown POP3 command
•142:2 (pop) unknown POP3 response
•142:4 (pop) base64 decoding failed
•142:5 (pop) quoted-printable decoding failed
•142:7 (pop) Unix-to-Unix decoding failed
Peg counts:
•pop.packets: total packets processed (sum)
•pop.sessions: total pop sessions (sum)
•pop.concurrent_sessions: total concurrent pop sessions (now)
•pop.max_concurrent_sessions: maximum concurrent pop sessions (max)
•pop.b64_attachments: total base64 attachments decoded (sum)
•pop.b64_decoded_bytes: total base64 decoded bytes (sum)
•pop.qp_attachments: total quoted-printable attachments decoded (sum)
•pop.qp_decoded_bytes: total quoted-printable decoded bytes (sum)
•pop.uu_attachments: total uu attachments decoded (sum)
•pop.uu_decoded_bytes: total uu decoded bytes (sum)
•pop.non_encoded_attachments: total non-encoded attachments extracted (sum)
•pop.non_encoded_bytes: total non-encoded extracted bytes (sum)
Snort 3 User Manual 117 / 284
9.27 port_scan
What: detect various ip, icmp, tcp, and udp port or protocol scans
Type: inspector
Usage: context
Configuration:
• int port_scan.memcap = 1048576: maximum tracker memory in bytes { 1: }
• multi port_scan.protos = all: choose the protocols to monitor { tcp | udp | icmp | ip | all }
• multi port_scan.scan_types = all: choose type of scans to look for { portscan | portsweep | decoy_portscan | distributed_portscan
| all }
• string port_scan.watch_ip: list of CIDRs with optional ports to watch
• string port_scan.ignore_scanners: list of CIDRs with optional ports to ignore if the source of scan alerts
• string port_scan.ignore_scanned: list of CIDRs with optional ports to ignore if the destination of scan alerts
• bool port_scan.alert_all = false: alert on all events over threshold within window if true; else alert on first only
• bool port_scan.include_midstream = false: list of CIDRs with optional ports
• int port_scan.tcp_ports.scans = 100: scan attempts { 0: }
• int port_scan.tcp_ports.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.tcp_ports.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.tcp_ports.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.tcp_decoy.scans = 100: scan attempts { 0: }
• int port_scan.tcp_decoy.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.tcp_decoy.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.tcp_decoy.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.tcp_sweep.scans = 100: scan attempts { 0: }
• int port_scan.tcp_sweep.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.tcp_sweep.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.tcp_sweep.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.tcp_dist.scans = 100: scan attempts { 0: }
• int port_scan.tcp_dist.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.tcp_dist.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.tcp_dist.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.udp_ports.scans = 100: scan attempts { 0: }
• int port_scan.udp_ports.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.udp_ports.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.udp_ports.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.udp_decoy.scans = 100: scan attempts { 0: }
Snort 3 User Manual 118 / 284
• int port_scan.udp_decoy.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.udp_decoy.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.udp_decoy.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.udp_sweep.scans = 100: scan attempts { 0: }
• int port_scan.udp_sweep.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.udp_sweep.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.udp_sweep.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.udp_dist.scans = 100: scan attempts { 0: }
• int port_scan.udp_dist.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.udp_dist.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.udp_dist.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.ip_proto.scans = 100: scan attempts { 0: }
• int port_scan.ip_proto.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.ip_proto.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.ip_proto.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.ip_decoy.scans = 100: scan attempts { 0: }
• int port_scan.ip_decoy.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.ip_decoy.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.ip_decoy.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.ip_sweep.scans = 100: scan attempts { 0: }
• int port_scan.ip_sweep.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.ip_sweep.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.ip_sweep.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.ip_dist.scans = 100: scan attempts { 0: }
• int port_scan.ip_dist.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.ip_dist.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.ip_dist.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.icmp_sweep.scans = 100: scan attempts { 0: }
• int port_scan.icmp_sweep.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.icmp_sweep.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.icmp_sweep.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.tcp_window = 0: detection interval for all TCP scans { 0: }
• int port_scan.udp_window = 0: detection interval for all UDP scans { 0: }
• int port_scan.ip_window = 0: detection interval for all IP scans { 0: }
• int port_scan.icmp_window = 0: detection interval for all ICMP scans { 0: }
Snort 3 User Manual 119 / 284
Rules:
•122:1 (port_scan) TCP portscan
•122:2 (port_scan) TCP decoy portscan
•122:3 (port_scan) TCP portsweep
•122:4 (port_scan) TCP distributed portscan
•122:5 (port_scan) TCP filtered portscan
•122:6 (port_scan) TCP filtered decoy portscan
•122:7 (port_scan) TCP filtered portsweep
•122:8 (port_scan) TCP filtered distributed portscan
•122:9 (port_scan) IP protocol scan
•122:10 (port_scan) IP decoy protocol scan
•122:11 (port_scan) IP protocol sweep
•122:12 (port_scan) IP distributed protocol scan
•122:13 (port_scan) IP filtered protocol scan
•122:14 (port_scan) IP filtered decoy protocol scan
•122:15 (port_scan) IP filtered protocol sweep
•122:16 (port_scan) IP filtered distributed protocol scan
•122:17 (port_scan) UDP portscan
•122:18 (port_scan) UDP decoy portscan
•122:19 (port_scan) UDP portsweep
•122:20 (port_scan) UDP distributed portscan
•122:21 (port_scan) UDP filtered portscan
•122:22 (port_scan) UDP filtered decoy portscan
•122:23 (port_scan) UDP filtered portsweep
•122:24 (port_scan) UDP filtered distributed portscan
•122:25 (port_scan) ICMP sweep
•122:26 (port_scan) ICMP filtered sweep
•122:27 (port_scan) open port
Peg counts:
•port_scan.packets: total packets (sum)
Snort 3 User Manual 120 / 284
9.28 reg_test
What: The regression test inspector (rti) is used when special packet handling is required for a reg test
Type: inspector
Usage: context
Configuration:
• bool reg_test.test_daq_retry = true: test daq packet retry feature
Peg counts:
•reg_test.packets: total packets (sum)
•reg_test.retry_requests: total retry packets requested (sum)
•reg_test.retry_packets: total retried packets received (sum)
9.29 reputation
What: reputation inspection
Type: inspector
Usage: global
Configuration:
• string reputation.blacklist: blacklist file name with IP lists
• int reputation.memcap = 500: maximum total MB of memory allocated { 1:4095 }
• enum reputation.nested_ip = inner: IP to use when there is IP encapsulation { inner|outer|all }
• enum reputation.priority = whitelist: defines priority when there is a decision conflict during run-time { blacklist|whitelist }
• bool reputation.scan_local = false: inspect local address defined in RFC 1918
• enum reputation.white = unblack: specify the meaning of whitelist { unblack|trust }
• string reputation.whitelist: whitelist file name with IP lists
Rules:
•136:1 (reputation) packets blacklisted
•136:2 (reputation) packets whitelisted
•136:3 (reputation) packets monitored
Peg counts:
•reputation.packets: total packets processed (sum)
•reputation.blacklisted: number of packets blacklisted (sum)
•reputation.whitelisted: number of packets whitelisted (sum)
•reputation.monitored: number of packets monitored (sum)
•reputation.memory_allocated: total memory allocated (sum)
Snort 3 User Manual 121 / 284
9.30 rpc_decode
What: RPC inspector
Type: inspector
Usage: inspect
Rules:
•106:1 (rpc_decode) fragmented RPC records
•106:2 (rpc_decode) multiple RPC records
•106:3 (rpc_decode) large RPC record fragment
•106:4 (rpc_decode) incomplete RPC segment
•106:5 (rpc_decode) zero-length RPC fragment
Peg counts:
•rpc_decode.total_packets: total packets (sum)
•rpc_decode.concurrent_sessions: total concurrent rpc sessions (now)
•rpc_decode.max_concurrent_sessions: maximum concurrent rpc sessions (max)
9.31 sip
What: sip inspection
Type: inspector
Usage: inspect
Configuration:
• bool sip.ignore_call_channel = false: enables the support for ignoring audio/video data channel
• int sip.max_call_id_len = 256: maximum call id field size { 0:65535 }
• int sip.max_contact_len = 256: maximum contact field size { 0:65535 }
• int sip.max_content_len = 1024: maximum content length of the message body { 0:65535 }
• int sip.max_dialogs = 4: maximum number of dialogs within one stream session { 1:4194303 }
• int sip.max_from_len = 256: maximum from field size { 0:65535 }
• int sip.max_requestName_len = 20: maximum request name field size { 0:65535 }
• int sip.max_to_len = 256: maximum to field size { 0:65535 }
• int sip.max_uri_len = 256: maximum request uri field size { 0:65535 }
• int sip.max_via_len = 1024: maximum via field size { 0:65535 }
• string sip.methods = invite cancel ack bye register options: list of methods to check in SIP messages
Rules:
•140:2 (sip) empty request URI
•140:3 (sip) URI is too long
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•140:4 (sip) empty call-Id
•140:5 (sip) Call-Id is too long
•140:6 (sip) CSeq number is too large or negative
•140:7 (sip) request name in CSeq is too long
•140:8 (sip) empty From header
•140:9 (sip) From header is too long
•140:10 (sip) empty To header
•140:11 (sip) To header is too long
•140:12 (sip) empty Via header
•140:13 (sip) Via header is too long
•140:14 (sip) empty Contact
•140:15 (sip) contact is too long
•140:16 (sip) content length is too large or negative
•140:17 (sip) multiple SIP messages in a packet
•140:18 (sip) content length mismatch
•140:19 (sip) request name is invalid
•140:20 (sip) Invite replay attack
•140:21 (sip) illegal session information modification
•140:22 (sip) response status code is not a 3 digit number
•140:23 (sip) empty Content-type header
•140:24 (sip) SIP version is invalid
•140:25 (sip) mismatch in METHOD of request and the CSEQ header
•140:26 (sip) method is unknown
•140:27 (sip) maximum dialogs within a session reached
Peg counts:
•sip.packets: total packets (sum)
•sip.sessions: total sessions (sum)
•sip.concurrent_sessions: total concurrent SIP sessions (now)
•sip.max_concurrent_sessions: maximum concurrent SIP sessions (max)
•sip.events: events generated (sum)
•sip.dialogs: total dialogs (sum)
•sip.ignored_channels: total channels ignored (sum)
•sip.ignored_sessions: total sessions ignored (sum)
•sip.total_requests: total requests (sum)
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•sip.invite: invite (sum)
•sip.cancel: cancel (sum)
•sip.ack: ack (sum)
•sip.bye: bye (sum)
•sip.register: register (sum)
•sip.options: options (sum)
•sip.refer: refer (sum)
•sip.subscribe: subscribe (sum)
•sip.update: update (sum)
•sip.join: join (sum)
•sip.info: info (sum)
•sip.message: message (sum)
•sip.notify: notify (sum)
•sip.prack: prack (sum)
•sip.total_responses: total responses (sum)
•sip.code_1xx: 1xx (sum)
•sip.code_2xx: 2xx (sum)
•sip.code_3xx: 3xx (sum)
•sip.code_4xx: 4xx (sum)
•sip.code_5xx: 5xx (sum)
•sip.code_6xx: 6xx (sum)
•sip.code_7xx: 7xx (sum)
•sip.code_8xx: 8xx (sum)
•sip.code_9xx: 9xx (sum)
9.32 smtp
What: smtp inspection
Type: inspector
Usage: inspect
Configuration:
• string smtp.alt_max_command_line_len[].command: command string
• int smtp.alt_max_command_line_len[].length = 0: specify non-default maximum for command { 0: }
• string smtp.auth_cmds: commands that initiate an authentication exchange
• string smtp.binary_data_cmds: commands that initiate sending of data and use a length value after the command
• int smtp.bitenc_decode_depth = 25: depth used to extract the non-encoded MIME attachments { -1:65535 }
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• int smtp.b64_decode_depth = 25: depth used to decode the base64 encoded MIME attachments { -1:65535 }
• string smtp.data_cmds: commands that initiate sending of data with an end of data delimiter
• int smtp.email_hdrs_log_depth = 1464: depth for logging email headers { 0:20480 }
• bool smtp.ignore_data = false: ignore data section of mail
• bool smtp.ignore_tls_data = false: ignore TLS-encrypted data when processing rules
• string smtp.invalid_cmds: alert if this command is sent from client side
• bool smtp.log_email_hdrs = false: log the SMTP email headers extracted from SMTP data
• bool smtp.log_filename = false: log the MIME attachment filenames extracted from the Content-Disposition header within
the MIME body
• bool smtp.log_mailfrom = false: log the sender’s email address extracted from the MAIL FROM command
• bool smtp.log_rcptto = false: log the recipient’s email address extracted from the RCPT TO command
• int smtp.max_auth_command_line_len = 1000: max auth command Line Length { 0:65535 }
• int smtp.max_command_line_len = 0: max Command Line Length { 0:65535 }
• int smtp.max_header_line_len = 0: max SMTP DATA header line { 0:65535 }
• int smtp.max_response_line_len = 0: max SMTP response line { 0:65535 }
• enum smtp.normalize = none: turns on/off normalization { none | cmds | all }
• string smtp.normalize_cmds: list of commands to normalize
• int smtp.qp_decode_depth = 25: quoted-Printable decoding depth { -1:65535 }
• int smtp.uu_decode_depth = 25: unix-to-Unix decoding depth { -1:65535 }
• string smtp.valid_cmds: list of valid commands
• enum smtp.xlink2state = alert: enable/disable xlink2state alert { disable | alert | drop }
Rules:
•124:1 (smtp) attempted command buffer overflow
•124:2 (smtp) attempted data header buffer overflow
•124:3 (smtp) attempted response buffer overflow
•124:4 (smtp) attempted specific command buffer overflow
•124:5 (smtp) unknown command
•124:6 (smtp) illegal command
•124:7 (smtp) attempted header name buffer overflow
•124:8 (smtp) attempted X-Link2State command buffer overflow
•124:10 (smtp) base64 decoding failed
•124:11 (smtp) quoted-printable decoding failed
•124:13 (smtp) Unix-to-Unix decoding failed
•124:14 (smtp) Cyrus SASL authentication attack
•124:15 (smtp) attempted authentication command buffer overflow
Snort 3 User Manual 125 / 284
Peg counts:
•smtp.packets: total packets processed (sum)
•smtp.sessions: total smtp sessions (sum)
•smtp.concurrent_sessions: total concurrent smtp sessions (now)
•smtp.max_concurrent_sessions: maximum concurrent smtp sessions (max)
•smtp.b64_attachments: total base64 attachments decoded (sum)
•smtp.b64_decoded_bytes: total base64 decoded bytes (sum)
•smtp.qp_attachments: total quoted-printable attachments decoded (sum)
•smtp.qp_decoded_bytes: total quoted-printable decoded bytes (sum)
•smtp.uu_attachments: total uu attachments decoded (sum)
•smtp.uu_decoded_bytes: total uu decoded bytes (sum)
•smtp.non_encoded_attachments: total non-encoded attachments extracted (sum)
•smtp.non_encoded_bytes: total non-encoded extracted bytes (sum)
9.33 ssh
What: ssh inspection
Type: inspector
Usage: inspect
Configuration:
• int ssh.max_encrypted_packets = 25: ignore session after this many encrypted packets { 0:65535 }
• int ssh.max_client_bytes = 19600: number of unanswered bytes before alerting on challenge-response overflow or CRC32 {
0:65535 }
• int ssh.max_server_version_len = 80: limit before alerting on secure CRT server version string overflow { 0:255 }
Rules:
•128:1 (ssh) challenge-response overflow exploit
•128:2 (ssh) SSH1 CRC32 exploit
•128:3 (ssh) server version string overflow
•128:5 (ssh) bad message direction
•128:6 (ssh) payload size incorrect for the given payload
•128:7 (ssh) failed to detect SSH version string
Peg counts:
•ssh.packets: total packets (sum)
•ssh.concurrent_sessions: total concurrent ssh sessions (now)
•ssh.max_concurrent_sessions: maximum concurrent ssh sessions (max)
Snort 3 User Manual 126 / 284
9.34 ssl
What: ssl inspection
Type: inspector
Usage: inspect
Configuration:
• bool ssl.trust_servers = false: disables requirement that application (encrypted) data must be observed on both sides
• int ssl.max_heartbeat_length = 0: maximum length of heartbeat record allowed { 0:65535 }
Rules:
•137:1 (ssl) invalid client HELLO after server HELLO detected
•137:2 (ssl) invalid server HELLO without client HELLO detected
•137:3 (ssl) heartbeat read overrun attempt detected
•137:4 (ssl) large heartbeat response detected
Peg counts:
•ssl.packets: total packets processed (sum)
•ssl.decoded: ssl packets decoded (sum)
•ssl.client_hello: total client hellos (sum)
•ssl.server_hello: total server hellos (sum)
•ssl.certificate: total ssl certificates (sum)
•ssl.server_done: total server done (sum)
•ssl.client_key_exchange: total client key exchanges (sum)
•ssl.server_key_exchange: total server key exchanges (sum)
•ssl.change_cipher: total change cipher records (sum)
•ssl.finished: total handshakes finished (sum)
•ssl.client_application: total client application records (sum)
•ssl.server_application: total server application records (sum)
•ssl.alert: total ssl alert records (sum)
•ssl.unrecognized_records: total unrecognized records (sum)
•ssl.handshakes_completed: total completed ssl handshakes (sum)
•ssl.bad_handshakes: total bad handshakes (sum)
•ssl.sessions_ignored: total sessions ignore (sum)
•ssl.detection_disabled: total detection disabled (sum)
•ssl.concurrent_sessions: total concurrent ssl sessions (now)
•ssl.max_concurrent_sessions: maximum concurrent ssl sessions (max)
Snort 3 User Manual 127 / 284
9.35 stream
What: common flow tracking
Type: inspector
Usage: global
Configuration:
• int stream.footprint = 0: use zero for production, non-zero for testing at given size (for TCP and user) { 0: }
• bool stream.ip_frags_only = false: don’t process non-frag flows
• int stream.ip_cache.max_sessions = 16384: maximum simultaneous sessions tracked before pruning { 2: }
• int stream.ip_cache.pruning_timeout = 30: minimum inactive time before being eligible for pruning { 1: }
• int stream.ip_cache.idle_timeout = 180: maximum inactive time before retiring session tracker { 1: }
• int stream.icmp_cache.max_sessions = 65536: maximum simultaneous sessions tracked before pruning { 2: }
• int stream.icmp_cache.pruning_timeout = 30: minimum inactive time before being eligible for pruning { 1: }
• int stream.icmp_cache.idle_timeout = 180: maximum inactive time before retiring session tracker { 1: }
• int stream.tcp_cache.max_sessions = 262144: maximum simultaneous sessions tracked before pruning { 2: }
• int stream.tcp_cache.pruning_timeout = 30: minimum inactive time before being eligible for pruning { 1: }
• int stream.tcp_cache.idle_timeout = 3600: maximum inactive time before retiring session tracker { 1: }
• int stream.udp_cache.max_sessions = 131072: maximum simultaneous sessions tracked before pruning { 2: }
• int stream.udp_cache.pruning_timeout = 30: minimum inactive time before being eligible for pruning { 1: }
• int stream.udp_cache.idle_timeout = 180: maximum inactive time before retiring session tracker { 1: }
• int stream.user_cache.max_sessions = 1024: maximum simultaneous sessions tracked before pruning { 2: }
• int stream.user_cache.pruning_timeout = 30: minimum inactive time before being eligible for pruning { 1: }
• int stream.user_cache.idle_timeout = 180: maximum inactive time before retiring session tracker { 1: }
• int stream.file_cache.max_sessions = 128: maximum simultaneous sessions tracked before pruning { 2: }
• int stream.file_cache.pruning_timeout = 30: minimum inactive time before being eligible for pruning { 1: }
• int stream.file_cache.idle_timeout = 180: maximum inactive time before retiring session tracker { 1: }
Peg counts:
•stream.ip_flows: total ip sessions (sum)
•stream.ip_total_prunes: total ip sessions pruned (sum)
•stream.ip_idle_prunes: ip sessions pruned due to timeout (sum)
•stream.ip_excess_prunes: ip sessions pruned due to excess (sum)
•stream.ip_uni_prunes: ip uni sessions pruned (sum)
•stream.ip_preemptive_prunes: ip sessions pruned during preemptive pruning (sum)
•stream.ip_memcap_prunes: ip sessions pruned due to memcap (sum)
•stream.ip_ha_prunes: ip sessions pruned by high availability sync (sum)
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•stream.icmp_flows: total icmp sessions (sum)
•stream.icmp_total_prunes: total icmp sessions pruned (sum)
•stream.icmp_idle_prunes: icmp sessions pruned due to timeout (sum)
•stream.icmp_excess_prunes: icmp sessions pruned due to excess (sum)
•stream.icmp_uni_prunes: icmp uni sessions pruned (sum)
•stream.icmp_preemptive_prunes: icmp sessions pruned during preemptive pruning (sum)
•stream.icmp_memcap_prunes: icmp sessions pruned due to memcap (sum)
•stream.icmp_ha_prunes: icmp sessions pruned by high availability sync (sum)
•stream.tcp_flows: total tcp sessions (sum)
•stream.tcp_total_prunes: total tcp sessions pruned (sum)
•stream.tcp_idle_prunes: tcp sessions pruned due to timeout (sum)
•stream.tcp_excess_prunes: tcp sessions pruned due to excess (sum)
•stream.tcp_uni_prunes: tcp uni sessions pruned (sum)
•stream.tcp_preemptive_prunes: tcp sessions pruned during preemptive pruning (sum)
•stream.tcp_memcap_prunes: tcp sessions pruned due to memcap (sum)
•stream.tcp_ha_prunes: tcp sessions pruned by high availability sync (sum)
•stream.udp_flows: total udp sessions (sum)
•stream.udp_total_prunes: total udp sessions pruned (sum)
•stream.udp_idle_prunes: udp sessions pruned due to timeout (sum)
•stream.udp_excess_prunes: udp sessions pruned due to excess (sum)
•stream.udp_uni_prunes: udp uni sessions pruned (sum)
•stream.udp_preemptive_prunes: udp sessions pruned during preemptive pruning (sum)
•stream.udp_memcap_prunes: udp sessions pruned due to memcap (sum)
•stream.udp_ha_prunes: udp sessions pruned by high availability sync (sum)
•stream.user_flows: total user sessions (sum)
•stream.user_total_prunes: total user sessions pruned (sum)
•stream.user_idle_prunes: user sessions pruned due to timeout (sum)
•stream.user_excess_prunes: user sessions pruned due to excess (sum)
•stream.user_uni_prunes: user uni sessions pruned (sum)
•stream.user_preemptive_prunes: user sessions pruned during preemptive pruning (sum)
•stream.user_memcap_prunes: user sessions pruned due to memcap (sum)
•stream.user_ha_prunes: user sessions pruned by high availability sync (sum)
•stream.file_flows: total file sessions (sum)
•stream.file_total_prunes: total file sessions pruned (sum)
•stream.file_idle_prunes: file sessions pruned due to timeout (sum)
Snort 3 User Manual 129 / 284
•stream.file_excess_prunes: file sessions pruned due to excess (sum)
•stream.file_uni_prunes: file uni sessions pruned (sum)
•stream.file_preemptive_prunes: file sessions pruned during preemptive pruning (sum)
•stream.file_memcap_prunes: file sessions pruned due to memcap (sum)
•stream.file_ha_prunes: file sessions pruned by high availability sync (sum)
9.36 stream_file
What: stream inspector for file flow tracking and processing
Type: inspector
Usage: inspect
Configuration:
• bool stream_file.upload = false: indicate file transfer direction
9.37 stream_icmp
What: stream inspector for ICMP flow tracking
Type: inspector
Usage: inspect
Configuration:
• int stream_icmp.session_timeout = 30: session tracking timeout { 1:86400 }
Peg counts:
•stream_icmp.sessions: total icmp sessions (sum)
•stream_icmp.max: max icmp sessions (max)
•stream_icmp.created: icmp session trackers created (sum)
•stream_icmp.released: icmp session trackers released (sum)
•stream_icmp.timeouts: icmp session timeouts (sum)
•stream_icmp.prunes: icmp session prunes (sum)
9.38 stream_ip
What: stream inspector for IP flow tracking and defragmentation
Type: inspector
Usage: inspect
Configuration:
• int stream_ip.max_frags = 8192: maximum number of simultaneous fragments being tracked { 1: }
• int stream_ip.max_overlaps = 0: maximum allowed overlaps per datagram; 0 is unlimited { 0: }
• int stream_ip.min_frag_length = 0: alert if fragment length is below this limit before or after trimming { 0: }
Snort 3 User Manual 130 / 284
• int stream_ip.min_ttl = 1: discard fragments with TTL below the minimum { 1:255 }
• enum stream_ip.policy = linux: fragment reassembly policy { first | linux | bsd | bsd_right | last | windows | solaris }
• int stream_ip.session_timeout = 30: session tracking timeout { 1:86400 }
• int stream_ip.trace: mask for enabling debug traces in module
Rules:
•123:1 (stream_ip) inconsistent IP options on fragmented packets
•123:2 (stream_ip) teardrop attack
•123:3 (stream_ip) short fragment, possible DOS attempt
•123:4 (stream_ip) fragment packet ends after defragmented packet
•123:5 (stream_ip) zero-byte fragment packet
•123:6 (stream_ip) bad fragment size, packet size is negative
•123:7 (stream_ip) bad fragment size, packet size is greater than 65536
•123:8 (stream_ip) fragmentation overlap
•123:11 (stream_ip) TTL value less than configured minimum, not using for reassembly
•123:12 (stream_ip) excessive fragment overlap
•123:13 (stream_ip) tiny fragment
Peg counts:
•stream_ip.sessions: total ip sessions (sum)
•stream_ip.max: max ip sessions (max)
•stream_ip.created: ip session trackers created (sum)
•stream_ip.released: ip session trackers released (sum)
•stream_ip.timeouts: ip session timeouts (sum)
•stream_ip.prunes: ip session prunes (sum)
•stream_ip.total_frags: total fragments (sum)
•stream_ip.current_frags: current fragments (now)
•stream_ip.max_frags: max fragments (sum)
•stream_ip.reassembled: reassembled datagrams (sum)
•stream_ip.discards: fragments discarded (sum)
•stream_ip.frag_timeouts: datagrams abandoned (sum)
•stream_ip.overlaps: overlapping fragments (sum)
•stream_ip.anomalies: anomalies detected (sum)
•stream_ip.alerts: alerts generated (sum)
•stream_ip.drops: fragments dropped (sum)
•stream_ip.trackers_added: datagram trackers created (sum)
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•stream_ip.trackers_freed: datagram trackers released (sum)
•stream_ip.trackers_cleared: datagram trackers cleared (sum)
•stream_ip.trackers_completed: datagram trackers completed (sum)
•stream_ip.nodes_inserted: fragments added to tracker (sum)
•stream_ip.nodes_deleted: fragments deleted from tracker (sum)
•stream_ip.memory_used: current memory usage in bytes (now)
•stream_ip.reassembled_bytes: total reassembled bytes (sum)
•stream_ip.fragmented_bytes: total fragmented bytes (sum)
9.39 stream_tcp
What: stream inspector for TCP flow tracking and stream normalization and reassembly
Type: inspector
Usage: inspect
Configuration:
• int stream_tcp.flush_factor = 0: flush upon seeing a drop in segment size after given number of non-decreasing segments {
0: }
• bool stream_tcp.ignore_any_rules = false: process TCP content rules w/o ports only if rules with ports are present
• int stream_tcp.max_window = 0: maximum allowed TCP window { 0:1073725440 }
• int stream_tcp.overlap_limit = 0: maximum number of allowed overlapping segments per session { 0:255 }
• int stream_tcp.max_pdu = 16384: maximum reassembled PDU size { 1460:32768 }
• enum stream_tcp.policy = bsd: determines operating system characteristics like reassembly { first | last | linux | old_linux |
bsd | macos | solaris | irix | hpux11 | hpux10 | windows | win_2003 | vista | proxy }
• bool stream_tcp.reassemble_async = true: queue data for reassembly before traffic is seen in both directions
• int stream_tcp.require_3whs = -1: don’t track midstream sessions after given seconds from start up; -1 tracks all { -1:86400
}
• bool stream_tcp.show_rebuilt_packets = false: enable cmg like output of reassembled packets
• int stream_tcp.queue_limit.max_bytes = 1048576: don’t queue more than given bytes per session and direction { 0: }
• int stream_tcp.queue_limit.max_segments = 2621: don’t queue more than given segments per session and direction { 0: }
• int stream_tcp.small_segments.count = 0: limit number of small segments queued { 0:2048 }
• int stream_tcp.small_segments.maximum_size = 0: limit number of small segments queued { 0:2048 }
• int stream_tcp.session_timeout = 30: session tracking timeout { 1:86400 }
Rules:
•129:1 (stream_tcp) SYN on established session
•129:2 (stream_tcp) data on SYN packet
•129:3 (stream_tcp) data sent on stream not accepting data
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•129:4 (stream_tcp) TCP timestamp is outside of PAWS window
•129:5 (stream_tcp) bad segment, adjusted size ⇐0 (deprecated)
•129:6 (stream_tcp) window size (after scaling) larger than policy allows
•129:7 (stream_tcp) limit on number of overlapping TCP packets reached
•129:8 (stream_tcp) data sent on stream after TCP reset sent
•129:9 (stream_tcp) TCP client possibly hijacked, different ethernet address
•129:10 (stream_tcp) TCP server possibly hijacked, different ethernet address
•129:11 (stream_tcp) TCP data with no TCP flags set
•129:12 (stream_tcp) consecutive TCP small segments exceeding threshold
•129:13 (stream_tcp) 4-way handshake detected
•129:14 (stream_tcp) TCP timestamp is missing
•129:15 (stream_tcp) reset outside window
•129:16 (stream_tcp) FIN number is greater than prior FIN
•129:17 (stream_tcp) ACK number is greater than prior FIN
•129:18 (stream_tcp) data sent on stream after TCP reset received
•129:19 (stream_tcp) TCP window closed before receiving data
•129:20 (stream_tcp) TCP session without 3-way handshake
Peg counts:
•stream_tcp.sessions: total tcp sessions (sum)
•stream_tcp.max: max tcp sessions (max)
•stream_tcp.created: tcp session trackers created (sum)
•stream_tcp.released: tcp session trackers released (sum)
•stream_tcp.timeouts: tcp session timeouts (sum)
•stream_tcp.prunes: tcp session prunes (sum)
•stream_tcp.resyns: SYN received on established session (sum)
•stream_tcp.discards: tcp packets discarded (sum)
•stream_tcp.events: events generated (sum)
•stream_tcp.ignored: tcp packets ignored (sum)
•stream_tcp.untracked: tcp packets not tracked (sum)
•stream_tcp.syn_trackers: tcp session tracking started on syn (sum)
•stream_tcp.syn_ack_trackers: tcp session tracking started on syn-ack (sum)
•stream_tcp.three_way_trackers: tcp session tracking started on ack (sum)
•stream_tcp.data_trackers: tcp session tracking started on data (sum)
•stream_tcp.segs_queued: total segments queued (sum)
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•stream_tcp.segs_released: total segments released (sum)
•stream_tcp.segs_split: tcp segments split when reassembling PDUs (sum)
•stream_tcp.segs_used: queued tcp segments applied to reassembled PDUs (sum)
•stream_tcp.rebuilt_packets: total reassembled PDUs (sum)
•stream_tcp.rebuilt_buffers: rebuilt PDU sections (sum)
•stream_tcp.rebuilt_bytes: total rebuilt bytes (sum)
•stream_tcp.overlaps: overlapping segments queued (sum)
•stream_tcp.gaps: missing data between PDUs (sum)
•stream_tcp.exceeded_max_segs: number of times the maximum queued segment limit was reached (sum)
•stream_tcp.exceeded_max_bytes: number of times the maximum queued byte limit was reached (sum)
•stream_tcp.internal_events: 135:X events generated (sum)
•stream_tcp.client_cleanups: number of times data from server was flushed when session released (sum)
•stream_tcp.server_cleanups: number of times data from client was flushed when session released (sum)
•stream_tcp.memory: current memory in use (now)
•stream_tcp.initializing: number of sessions currently initializing (now)
•stream_tcp.established: number of sessions currently established (now)
•stream_tcp.closing: number of sessions currently closing (now)
•stream_tcp.syns: number of syn packets (sum)
•stream_tcp.syn_acks: number of syn-ack packets (sum)
•stream_tcp.resets: number of reset packets (sum)
•stream_tcp.fins: number of fin packets (sum)
9.40 stream_udp
What: stream inspector for UDP flow tracking
Type: inspector
Usage: inspect
Configuration:
• int stream_udp.session_timeout = 30: session tracking timeout { 1:86400 }
• bool stream_udp.ignore_any_rules = false: process UDP content rules w/o ports only if rules with ports are present
Peg counts:
•stream_udp.sessions: total udp sessions (sum)
•stream_udp.max: max udp sessions (max)
•stream_udp.created: udp session trackers created (sum)
•stream_udp.released: udp session trackers released (sum)
•stream_udp.timeouts: udp session timeouts (sum)
•stream_udp.prunes: udp session prunes (sum)
•stream_udp.ignored: udp packets ignored (sum)
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9.41 stream_user
What: stream inspector for user flow tracking and reassembly
Type: inspector
Usage: inspect
Configuration:
• int stream_user.session_timeout = 30: session tracking timeout { 1:86400 }
• int stream_user.trace: mask for enabling debug traces in module
9.42 telnet
What: telnet inspection and normalization
Type: inspector
Usage: inspect
Configuration:
• int telnet.ayt_attack_thresh = -1: alert on this number of consecutive Telnet AYT commands { -1: }
• bool telnet.check_encrypted = false: check for end of encryption
• bool telnet.encrypted_traffic = false: check for encrypted Telnet and FTP
• bool telnet.normalize = false: eliminate escape sequences
Rules:
•126:1 (telnet) consecutive Telnet AYT commands beyond threshold
•126:2 (telnet) Telnet traffic encrypted
•126:3 (telnet) Telnet subnegotiation begin command without subnegotiation end
Peg counts:
•telnet.total_packets: total packets (sum)
•telnet.concurrent_sessions: total concurrent Telnet sessions (now)
•telnet.max_concurrent_sessions: maximum concurrent Telnet sessions (max)
9.43 wizard
What: inspector that implements port-independent protocol identification
Type: inspector
Usage: inspect
Configuration:
• string wizard.hexes[].service: name of service
• select wizard.hexes[].proto = tcp: protocol to scan { tcp | udp }
• bool wizard.hexes[].client_first = true: which end initiates data transfer
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• string wizard.hexes[].to_server[].hex: sequence of data with wild chars (?)
• string wizard.hexes[].to_client[].hex: sequence of data with wild chars (?)
• string wizard.spells[].service: name of service
• select wizard.spells[].proto = tcp: protocol to scan { tcp | udp }
• bool wizard.spells[].client_first = true: which end initiates data transfer
• string wizard.spells[].to_server[].spell: sequence of data with wild cards (*)
• string wizard.spells[].to_client[].spell: sequence of data with wild cards (*)
• multi wizard.curses: enable service identification based on internal algorithm { dce_smb | dce_udp | dce_tcp }
Peg counts:
•wizard.tcp_scans: tcp payload scans (sum)
•wizard.tcp_hits: tcp identifications (sum)
•wizard.udp_scans: udp payload scans (sum)
•wizard.udp_hits: udp identifications (sum)
•wizard.user_scans: user payload scans (sum)
•wizard.user_hits: user identifications (sum)
10 IPS Action Modules
IPS actions allow you to perform custom actions when events are generated. Unlike loggers, these are invoked before thresholding
and can be used to control external agents.
Externally defined actions must be configured to become available to the parser. For the reject rule, you can set reject = { } to
get the rule to parse.
10.1 react
What: send response to client and terminate session
Type: ips_action
Usage: detect
Configuration:
• bool react.msg = false: use rule msg in response page instead of default message
• string react.page: file containing HTTP response (headers and body)
10.2 reject
What: terminate session with TCP reset or ICMP unreachable
Type: ips_action
Usage: detect
Configuration:
• enum reject.reset: send TCP reset to one or both ends { source|dest|both }
• enum reject.control: send ICMP unreachable(s) { network|host|port|all }
Snort 3 User Manual 136 / 284
10.3 rewrite
What: overwrite packet contents
Type: ips_action
Usage: detect
Configuration:
• bool rewrite.disable_replace = false: disable replace of packet contents with rewrite rules
11 IPS Option Modules
IPS options are the building blocks of IPS rules.
11.1 ack
What: rule option to match on TCP ack numbers
Type: ips_option
Usage: detect
Configuration:
• interval ack.~range: check if TCP ack value is value | min<>max | <max | >min { 0: }
11.2 appids
What: detection option for application ids
Type: ips_option
Usage: detect
Configuration:
• string appids.~: comma separated list of application names
11.3 asn1
What: rule option for asn1 detection
Type: ips_option
Usage: detect
Configuration:
• implied asn1.bitstring_overflow: detects invalid bitstring encodings that are known to be remotely exploitable
• implied asn1.double_overflow: detects a double ASCII encoding that is larger than a standard buffer
• implied asn1.print: dump decode data to console; always true
• int asn1.oversize_length: compares ASN.1 type lengths with the supplied argument { 0: }
• int asn1.absolute_offset: absolute offset from the beginning of the packet { 0: }
• int asn1.relative_offset: relative offset from the cursor
Snort 3 User Manual 137 / 284
11.4 base64_decode
What: rule option to decode base64 data - must be used with base64_data option
Type: ips_option
Usage: detect
Configuration:
• int base64_decode.bytes: number of base64 encoded bytes to decode { 1: }
• int base64_decode.offset = 0: bytes past start of buffer to start decoding { 0: }
• implied base64_decode.relative: apply offset to cursor instead of start of buffer
11.5 bufferlen
What: rule option to check length of current buffer
Type: ips_option
Usage: detect
Configuration:
• interval bufferlen.~range: check that length of current buffer is in given range { 0:65535 }
11.6 byte_extract
What: rule option to convert data to an integer variable
Type: ips_option
Usage: detect
Configuration:
• int byte_extract.~count: number of bytes to pick up from the buffer { 1:10 }
• int byte_extract.~offset: number of bytes into the buffer to start processing { -65535:65535 }
• string byte_extract.~name: name of the variable that will be used in other rule options
• implied byte_extract.relative: offset from cursor instead of start of buffer
• int byte_extract.multiplier = 1: scale extracted value by given amount { 1:65535 }
• int byte_extract.align = 0: round the number of converted bytes up to the next 2- or 4-byte boundary { 0:4 }
• implied byte_extract.big: big endian
• implied byte_extract.little: little endian
• implied byte_extract.dce: dcerpc2 determines endianness
• implied byte_extract.string: convert from string
• implied byte_extract.hex: convert from hex string
• implied byte_extract.oct: convert from octal string
• implied byte_extract.dec: convert from decimal string
• int byte_extract.bitmask: applies as an AND to the extracted value before storage in name { 0x1:0xFFFFFFFF }
Snort 3 User Manual 138 / 284
11.7 byte_jump
What: rule option to move the detection cursor
Type: ips_option
Usage: detect
Configuration:
• int byte_jump.~count: number of bytes to pick up from the buffer { 0:10 }
• string byte_jump.~offset: variable name or number of bytes into the buffer to start processing
• implied byte_jump.relative: offset from cursor instead of start of buffer
• implied byte_jump.from_beginning: jump from start of buffer instead of cursor
• implied byte_jump.from_end: jump backward from end of buffer
• int byte_jump.multiplier = 1: scale extracted value by given amount { 1:65535 }
• int byte_jump.align = 0: round the number of converted bytes up to the next 2- or 4-byte boundary { 0:4 }
• int byte_jump.post_offset = 0: also skip forward or backwards (positive of negative value) this number of bytes { -65535:65535
}
• implied byte_jump.big: big endian
• implied byte_jump.little: little endian
• implied byte_jump.dce: dcerpc2 determines endianness
• implied byte_jump.string: convert from string
• implied byte_jump.hex: convert from hex string
• implied byte_jump.oct: convert from octal string
• implied byte_jump.dec: convert from decimal string
• int byte_jump.bitmask: applies as an AND prior to evaluation { 0x1:0xFFFFFFFF }
11.8 byte_math
What: rule option to perform mathematical operations on extracted value and a specified value or existing variable
Type: ips_option
Usage: detect
Configuration:
• int byte_math.bytes: number of bytes to pick up from the buffer { 1:10 }
• string byte_math.offset: number of bytes into the buffer to start processing
• enum byte_math.oper: mathematical operation to perform { +|-|*|/|<<|>> }
• string byte_math.rvalue: value to use mathematical operation against
• string byte_math.result: name of the variable to store the result
• implied byte_math.relative: offset from cursor instead of start of buffer
• enum byte_math.endian: specify big/little endian { big|little }
• implied byte_math.dce: dcerpc2 determines endianness
• enum byte_math.string: convert extracted string to dec/hex/oct { hex|dec|oct }
• int byte_math.bitmask: applies as bitwise AND to the extracted value before storage in name { 0x1:0xFFFFFFFF }
Snort 3 User Manual 139 / 284
11.9 byte_test
What: rule option to convert data to integer and compare
Type: ips_option
Usage: detect
Configuration:
• int byte_test.~count: number of bytes to pick up from the buffer { 1:10 }
• string byte_test.~operator: variable name or number of bytes into the buffer to start processing
• string byte_test.~compare: variable name or value to test the converted result against
• string byte_test.~offset: variable name or number of bytes into the payload to start processing
• implied byte_test.relative: offset from cursor instead of start of buffer
• implied byte_test.big: big endian
• implied byte_test.little: little endian
• implied byte_test.dce: dcerpc2 determines endianness
• implied byte_test.string: convert from string
• implied byte_test.hex: convert from hex string
• implied byte_test.oct: convert from octal string
• implied byte_test.dec: convert from decimal string
• int byte_test.bitmask: applies as an AND prior to evaluation { 0x1:0xFFFFFFFF }
11.10 classtype
What: general rule option for rule classification
Type: ips_option
Usage: detect
Configuration:
• string classtype.~: classification for this rule
11.11 content
What: payload rule option for basic pattern matching
Type: ips_option
Usage: detect
Configuration:
• string content.~data: data to match
• implied content.nocase: case insensitive match
• implied content.fast_pattern: use this content in the fast pattern matcher instead of the content selected by default
Snort 3 User Manual 140 / 284
• int content.fast_pattern_offset = 0: number of leading characters of this content the fast pattern matcher should exclude { 0:
}
• int content.fast_pattern_length: maximum number of characters from this content the fast pattern matcher should use { 1: }
• string content.offset: var or number of bytes from start of buffer to start search
• string content.depth: var or maximum number of bytes to search from beginning of buffer
• string content.distance: var or number of bytes from cursor to start search
• string content.within: var or maximum number of bytes to search from cursor
11.12 cvs
What: payload rule option for detecting specific attacks
Type: ips_option
Usage: detect
Configuration:
• implied cvs.invalid-entry: looks for an invalid Entry string
11.13 dce_iface
What: detection option to check dcerpc interface
Type: ips_option
Usage: detect
Configuration:
• string dce_iface.uuid: match given dcerpc uuid
• interval dce_iface.version: interface version { 0: }
• implied dce_iface.any_frag: match on any fragment
11.14 dce_opnum
What: detection option to check dcerpc operation number
Type: ips_option
Usage: detect
Configuration:
• string dce_opnum.~: match given dcerpc operation number, range or list
11.15 dce_stub_data
What: sets the cursor to dcerpc stub data
Type: ips_option
Usage: detect
Snort 3 User Manual 141 / 284
11.16 detection_filter
What: rule option to require multiple hits before a rule generates an event
Type: ips_option
Usage: detect
Configuration:
• enum detection_filter.track: track hits by source or destination IP address { by_src | by_dst }
• int detection_filter.count: hits in interval before allowing the rule to fire { 1: }
• int detection_filter.seconds: length of interval to count hits { 1: }
11.17 dnp3_data
What: sets the cursor to dnp3 data
Type: ips_option
Usage: detect
11.18 dnp3_func
What: detection option to check DNP3 function code
Type: ips_option
Usage: detect
Configuration:
• string dnp3_func.~: match DNP3 function code or name
11.19 dnp3_ind
What: detection option to check DNP3 indicator flags
Type: ips_option
Usage: detect
Configuration:
• string dnp3_ind.~: match given DNP3 indicator flags
11.20 dnp3_obj
What: detection option to check DNP3 object headers
Type: ips_option
Usage: detect
Configuration:
• int dnp3_obj.group = 0: match given DNP3 object header group { 0:255 }
• int dnp3_obj.var = 0: match given DNP3 object header var { 0:255 }
Snort 3 User Manual 142 / 284
11.21 dsize
What: rule option to test payload size
Type: ips_option
Usage: detect
Configuration:
• interval dsize.~range: check if packet payload size is in the given range { 0:65535 }
11.22 file_data
What: rule option to set detection cursor to file data
Type: ips_option
Usage: detect
11.23 file_type
What: rule option to check file type
Type: ips_option
Usage: detect
Configuration:
• string file_type.~: list of file type IDs to match
11.24 flags
What: rule option to test TCP control flags
Type: ips_option
Usage: detect
Configuration:
• string flags.~test_flags: these flags are tested
• string flags.~mask_flags: these flags are don’t cares
11.25 flow
What: rule option to check session properties
Type: ips_option
Usage: detect
Configuration:
• implied flow.to_client: match on server responses
• implied flow.to_server: match on client requests
• implied flow.from_client: same as to_server
Snort 3 User Manual 143 / 284
• implied flow.from_server: same as to_client
• implied flow.established: match only during data transfer phase
• implied flow.not_established: match only outside data transfer phase
• implied flow.stateless: match regardless of stream state
• implied flow.no_stream: match on raw packets only
• implied flow.only_stream: match on reassembled packets only
• implied flow.no_frag: match on raw packets only
• implied flow.only_frag: match on defragmented packets only
11.26 flowbits
What: rule option to set and test arbitrary boolean flags
Type: ips_option
Usage: detect
Configuration:
• string flowbits.~command: set|reset|isset|etc.
• string flowbits.~arg1: bits or group
• string flowbits.~arg2: group if arg1 is bits
11.27 fragbits
What: rule option to test IP frag flags
Type: ips_option
Usage: detect
Configuration:
• string fragbits.~flags: these flags are tested
11.28 fragoffset
What: rule option to test IP frag offset
Type: ips_option
Usage: detect
Configuration:
• interval fragoffset.~range: check if ip fragment offset is in given range { 0:8192 }
11.29 gid
What: rule option specifying rule generator
Type: ips_option
Usage: detect
Configuration:
• int gid.~: generator id { 1: }
Snort 3 User Manual 144 / 284
11.30 gtp_info
What: rule option to check gtp info element
Type: ips_option
Usage: detect
Configuration:
• string gtp_info.~: info element to match
11.31 gtp_type
What: rule option to check gtp types
Type: ips_option
Usage: detect
Configuration:
• string gtp_type.~: list of types to match
11.32 gtp_version
What: rule option to check GTP version
Type: ips_option
Usage: detect
Configuration:
• int gtp_version.~: version to match { 0:2 }
11.33 http_client_body
What: rule option to set the detection cursor to the request body
Type: ips_option
Usage: detect
11.34 http_cookie
What: rule option to set the detection cursor to the HTTP cookie
Type: ips_option
Usage: detect
Configuration:
• implied http_cookie.request: match against the cookie from the request message even when examining the response
• implied http_cookie.with_body: parts of this rule examine HTTP message body
• implied http_cookie.with_trailer: parts of this rule examine HTTP message trailers
Snort 3 User Manual 145 / 284
11.35 http_header
What: rule option to set the detection cursor to the normalized headers
Type: ips_option
Usage: detect
Configuration:
• string http_header.field: restrict to given header. Header name is case insensitive.
• implied http_header.request: match against the headers from the request message even when examining the response
• implied http_header.with_body: parts of this rule examine HTTP message body
• implied http_header.with_trailer: parts of this rule examine HTTP message trailers
11.36 http_method
What: rule option to set the detection cursor to the HTTP request method
Type: ips_option
Usage: detect
Configuration:
• implied http_method.with_body: parts of this rule examine HTTP message body
• implied http_method.with_trailer: parts of this rule examine HTTP message trailers
11.37 http_raw_body
What: rule option to set the detection cursor to the unnormalized message body
Type: ips_option
Usage: detect
11.38 http_raw_cookie
What: rule option to set the detection cursor to the unnormalized cookie
Type: ips_option
Usage: detect
Configuration:
• implied http_raw_cookie.request: match against the cookie from the request message even when examining the response
• implied http_raw_cookie.with_body: parts of this rule examine HTTP message body
• implied http_raw_cookie.with_trailer: parts of this rule examine HTTP message trailers
Snort 3 User Manual 146 / 284
11.39 http_raw_header
What: rule option to set the detection cursor to the unnormalized headers
Type: ips_option
Usage: detect
Configuration:
• implied http_raw_header.request: match against the headers from the request message even when examining the response
• implied http_raw_header.with_body: parts of this rule examine HTTP message body
• implied http_raw_header.with_trailer: parts of this rule examine HTTP message trailers
11.40 http_raw_request
What: rule option to set the detection cursor to the unnormalized request line
Type: ips_option
Usage: detect
Configuration:
• implied http_raw_request.with_body: parts of this rule examine HTTP message body
• implied http_raw_request.with_trailer: parts of this rule examine HTTP message trailers
11.41 http_raw_status
What: rule option to set the detection cursor to the unnormalized status line
Type: ips_option
Usage: detect
Configuration:
• implied http_raw_status.with_body: parts of this rule examine HTTP message body
• implied http_raw_status.with_trailer: parts of this rule examine HTTP message trailers
11.42 http_raw_trailer
What: rule option to set the detection cursor to the unnormalized trailers
Type: ips_option
Usage: detect
Configuration:
• implied http_raw_trailer.request: match against the trailers from the request message even when examining the response
• implied http_raw_trailer.with_header: parts of this rule examine HTTP response message headers (must be combined with
request)
• implied http_raw_trailer.with_body: parts of this rule examine HTTP response message body (must be combined with
request)
Snort 3 User Manual 147 / 284
11.43 http_raw_uri
What: rule option to set the detection cursor to the unnormalized URI
Type: ips_option
Usage: detect
Configuration:
• implied http_raw_uri.with_body: parts of this rule examine HTTP message body
• implied http_raw_uri.with_trailer: parts of this rule examine HTTP message trailers
• implied http_raw_uri.scheme: match against scheme section of URI only
• implied http_raw_uri.host: match against host section of URI only
• implied http_raw_uri.port: match against port section of URI only
• implied http_raw_uri.path: match against path section of URI only
• implied http_raw_uri.query: match against query section of URI only
• implied http_raw_uri.fragment: match against fragment section of URI only
11.44 http_stat_code
What: rule option to set the detection cursor to the HTTP status code
Type: ips_option
Usage: detect
Configuration:
• implied http_stat_code.with_body: parts of this rule examine HTTP message body
• implied http_stat_code.with_trailer: parts of this rule examine HTTP message trailers
11.45 http_stat_msg
What: rule option to set the detection cursor to the HTTP status message
Type: ips_option
Usage: detect
Configuration:
• implied http_stat_msg.with_body: parts of this rule examine HTTP message body
• implied http_stat_msg.with_trailer: parts of this rule examine HTTP message trailers
Snort 3 User Manual 148 / 284
11.46 http_trailer
What: rule option to set the detection cursor to the normalized trailers
Type: ips_option
Usage: detect
Configuration:
• string http_trailer.field: restrict to given trailer
• implied http_trailer.request: match against the trailers from the request message even when examining the response
• implied http_trailer.with_header: parts of this rule examine HTTP response message headers (must be combined with re-
quest)
• implied http_trailer.with_body: parts of this rule examine HTTP message body (must be combined with request)
11.47 http_true_ip
What: rule option to set the detection cursor to the final client IP address
Type: ips_option
Usage: detect
Configuration:
• implied http_true_ip.with_body: parts of this rule examine HTTP message body
• implied http_true_ip.with_trailer: parts of this rule examine HTTP message trailers
11.48 http_uri
What: rule option to set the detection cursor to the normalized URI buffer
Type: ips_option
Usage: detect
Configuration:
• implied http_uri.with_body: parts of this rule examine HTTP message body
• implied http_uri.with_trailer: parts of this rule examine HTTP message trailers
• implied http_uri.scheme: match against scheme section of URI only
• implied http_uri.host: match against host section of URI only
• implied http_uri.port: match against port section of URI only
• implied http_uri.path: match against path section of URI only
• implied http_uri.query: match against query section of URI only
• implied http_uri.fragment: match against fragment section of URI only
Snort 3 User Manual 149 / 284
11.49 http_version
What: rule option to set the detection cursor to the version buffer
Type: ips_option
Usage: detect
Configuration:
• implied http_version.request: match against the version from the request message even when examining the response
• implied http_version.with_body: parts of this rule examine HTTP message body
• implied http_version.with_trailer: parts of this rule examine HTTP message trailers
11.50 icmp_id
What: rule option to check ICMP ID
Type: ips_option
Usage: detect
Configuration:
• interval icmp_id.~range: check if ICMP ID is in given range { 0:65535 }
11.51 icmp_seq
What: rule option to check ICMP sequence number
Type: ips_option
Usage: detect
Configuration:
• interval icmp_seq.~range: check if ICMP sequence number is in given range { 0:65535 }
11.52 icode
What: rule option to check ICMP code
Type: ips_option
Usage: detect
Configuration:
• interval icode.~range: check if ICMP code is in given range is { 0:255 }
11.53 id
What: rule option to check the IP ID field
Type: ips_option
Usage: detect
Configuration:
• interval id.~range: check if the IP ID is in the given range { 0: }
Snort 3 User Manual 150 / 284
11.54 ip_proto
What: rule option to check the IP protocol number
Type: ips_option
Usage: detect
Configuration:
• string ip_proto.~proto: [!|>|<] name or number
11.55 ipopts
What: rule option to check for IP options
Type: ips_option
Usage: detect
Configuration:
• select ipopts.~opt: output format { rr|eol|nop|ts|sec|esec|lsrr|lsrre|ssrr|satid|any }
11.56 isdataat
What: rule option to check for the presence of payload data
Type: ips_option
Usage: detect
Configuration:
• string isdataat.~length: num | !num
• implied isdataat.relative: offset from cursor instead of start of buffer
11.57 itype
What: rule option to check ICMP type
Type: ips_option
Usage: detect
Configuration:
• interval itype.~range: check if ICMP type is in given range { 0:255 }
11.58 md5
What: payload rule option for hash matching
Type: ips_option
Usage: detect
Configuration:
• string md5.~hash: data to match
• int md5.length: number of octets in plain text { 1:65535 }
• string md5.offset: var or number of bytes from start of buffer to start search
• implied md5.relative = false: offset from cursor instead of start of buffer
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11.59 metadata
What: rule option for conveying arbitrary name, value data within the rule text
Type: ips_option
Usage: detect
Configuration:
• string metadata.*: comma-separated list of arbitrary name value pairs
11.60 modbus_data
What: rule option to set cursor to modbus data
Type: ips_option
Usage: detect
11.61 modbus_func
What: rule option to check modbus function code
Type: ips_option
Usage: detect
Configuration:
• string modbus_func.~: function code to match
11.62 modbus_unit
What: rule option to check Modbus unit ID
Type: ips_option
Usage: detect
Configuration:
• int modbus_unit.~: Modbus unit ID { 0:255 }
11.63 msg
What: rule option summarizing rule purpose output with events
Type: ips_option
Usage: detect
Configuration:
• string msg.~: message describing rule
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11.64 mss
What: detection for TCP maximum segment size
Type: ips_option
Usage: detect
Configuration:
• interval mss.~range: check if TCP MSS is in given range { 0:65535 }
11.65 pcre
What: rule option for matching payload data with pcre
Type: ips_option
Usage: detect
Configuration:
• string pcre.~re: Snort regular expression
11.66 pkt_data
What: rule option to set the detection cursor to the normalized packet data
Type: ips_option
Usage: detect
11.67 pkt_num
What: alert on raw packet number
Type: ips_option
Usage: detect
Configuration:
• interval pkt_num.~range: check if packet number is in given range { 1: }
11.68 priority
What: rule option for prioritizing events
Type: ips_option
Usage: detect
Configuration:
• int priority.~: relative severity level; 1 is highest priority { 1: }
11.69 raw_data
What: rule option to set the detection cursor to the raw packet data
Type: ips_option
Usage: detect
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11.70 reference
What: rule option to indicate relevant attack identification system
Type: ips_option
Usage: detect
Configuration:
• string reference.~scheme: reference scheme
• string reference.~id: reference id
11.71 regex
What: rule option for matching payload data with hyperscan regex
Type: ips_option
Usage: detect
Configuration:
• string regex.~re: hyperscan regular expression
• implied regex.dotall: matching a . will not exclude newlines
• implied regex.fast_pattern: use this content in the fast pattern matcher instead of the content selected by default
• implied regex.multiline: ˆ and $ anchors match any newlines in data
• implied regex.nocase: case insensitive match
• implied regex.relative: start search from end of last match instead of start of buffer
11.72 rem
What: rule option to convey an arbitrary comment in the rule body
Type: ips_option
Usage: detect
Configuration:
• string rem.~: comment
11.73 replace
What: rule option to overwrite payload data; use with rewrite action
Type: ips_option
Usage: detect
Configuration:
• string replace.~: byte code to replace with
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11.74 rev
What: rule option to indicate current revision of signature
Type: ips_option
Usage: detect
Configuration:
• int rev.~: revision { 1: }
11.75 rpc
What: rule option to check SUNRPC CALL parameters
Type: ips_option
Usage: detect
Configuration:
• int rpc.~app: application number
• string rpc.~ver: version number or * for any
• string rpc.~proc: procedure number or * for any
11.76 sd_pattern
What: rule option for detecting sensitive data
Type: ips_option
Usage: detect
Configuration:
• string sd_pattern.~pattern: The pattern to search for
• int sd_pattern.threshold: number of matches before alerting { 1 }
Peg counts:
•sd_pattern.below_threshold: sd_pattern matched but missed threshold (sum)
•sd_pattern.pattern_not_found: sd_pattern did not not match (sum)
•sd_pattern.terminated: hyperscan terminated (sum)
11.77 seq
What: rule option to check TCP sequence number
Type: ips_option
Usage: detect
Configuration:
• interval seq.~range: check if TCP sequence number is in given range { 0: }
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11.78 service
What: rule option to specify list of services for grouping rules
Type: ips_option
Usage: detect
Configuration:
• string service.*: one or more comma-separated service names
11.79 session
What: rule option to check user data from TCP sessions
Type: ips_option
Usage: detect
Configuration:
• enum session.~mode: output format { printable|binary|all }
11.80 sha256
What: payload rule option for hash matching
Type: ips_option
Usage: detect
Configuration:
• string sha256.~hash: data to match
• int sha256.length: number of octets in plain text { 1:65535 }
• string sha256.offset: var or number of bytes from start of buffer to start search
• implied sha256.relative = false: offset from cursor instead of start of buffer
11.81 sha512
What: payload rule option for hash matching
Type: ips_option
Usage: detect
Configuration:
• string sha512.~hash: data to match
• int sha512.length: number of octets in plain text { 1:65535 }
• string sha512.offset: var or number of bytes from start of buffer to start search
• implied sha512.relative = false: offset from cursor instead of start of buffer
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11.82 sid
What: rule option to indicate signature number
Type: ips_option
Usage: detect
Configuration:
• int sid.~: signature id { 1: }
11.83 sip_body
What: rule option to set the detection cursor to the request body
Type: ips_option
Usage: detect
11.84 sip_header
What: rule option to set the detection cursor to the SIP header buffer
Type: ips_option
Usage: detect
11.85 sip_method
What: detection option for sip stat code
Type: ips_option
Usage: detect
Configuration:
• string sip_method.*method: sip method
11.86 sip_stat_code
What: detection option for sip stat code
Type: ips_option
Usage: detect
Configuration:
• int sip_stat_code.*code: stat code { 1:999 }
11.87 so
What: rule option to call custom eval function
Type: ips_option
Usage: detect
Configuration:
• string so.~func: name of eval function
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11.88 soid
What: rule option to specify a shared object rule ID
Type: ips_option
Usage: detect
Configuration:
• string soid.~: SO rule ID is unique key, eg <gid>_<sid>_<rev> like 3_45678_9
11.89 ssl_state
What: detection option for ssl state
Type: ips_option
Usage: detect
Configuration:
• implied ssl_state.client_hello: check for client hello
• implied ssl_state.server_hello: check for server hello
• implied ssl_state.client_keyx: check for client keyx
• implied ssl_state.server_keyx: check for server keyx
• implied ssl_state.unknown: check for unknown record
• implied ssl_state.!client_hello: check for records that are not client hello
• implied ssl_state.!server_hello: check for records that are not server hello
• implied ssl_state.!client_keyx: check for records that are not client keyx
• implied ssl_state.!server_keyx: check for records that are not server keyx
• implied ssl_state.!unknown: check for records that are not unknown
11.90 ssl_version
What: detection option for ssl version
Type: ips_option
Usage: detect
Configuration:
• implied ssl_version.sslv2: check for sslv2
• implied ssl_version.sslv3: check for sslv3
• implied ssl_version.tls1.0: check for tls1.0
• implied ssl_version.tls1.1: check for tls1.1
• implied ssl_version.tls1.2: check for tls1.2
• implied ssl_version.!sslv2: check for records that are not sslv2
• implied ssl_version.!sslv3: check for records that are not sslv3
• implied ssl_version.!tls1.0: check for records that are not tls1.0
• implied ssl_version.!tls1.1: check for records that are not tls1.1
• implied ssl_version.!tls1.2: check for records that are not tls1.2
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11.91 stream_reassemble
What: detection option for stream reassembly control
Type: ips_option
Usage: detect
Configuration:
• enum stream_reassemble.action: stop or start stream reassembly { disable|enable }
• enum stream_reassemble.direction: action applies to the given direction(s) { client|server|both }
• implied stream_reassemble.noalert: don’t alert when rule matches
• implied stream_reassemble.fastpath: optionally whitelist the remainder of the session
11.92 stream_size
What: detection option for stream size checking
Type: ips_option
Usage: detect
Configuration:
• interval stream_size.~range: check if the stream size is in the given range { 0: }
• enum stream_size.~direction: compare applies to the given direction(s) { either|to_server|to_client|both }
11.93 tag
What: rule option to log additional packets
Type: ips_option
Usage: detect
Configuration:
• enum tag.~: log all packets in session or all packets to or from host { session|host_src|host_dst }
• int tag.packets: tag this many packets { 1: }
• int tag.seconds: tag for this many seconds { 1: }
• int tag.bytes: tag for this many bytes { 1: }
11.94 target
What: rule option to indicate target of attack
Type: ips_option
Usage: detect
Configuration:
• enum target.~: indicate the target of the attack { src_ip | dst_ip }
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11.95 tos
What: rule option to check type of service field
Type: ips_option
Usage: detect
Configuration:
• interval tos.~range: check if IP TOS is in given range { 0:255 }
11.96 ttl
What: rule option to check time to live field
Type: ips_option
Usage: detect
Configuration:
• interval ttl.~range: check if IP TTL is in the given range { 0:255 }
11.97 urg
What: detection for TCP urgent pointer
Type: ips_option
Usage: detect
Configuration:
• interval urg.~range: check if tcp urgent offset is in given range { 0:65535 }
11.98 window
What: rule option to check TCP window field
Type: ips_option
Usage: detect
Configuration:
• interval window.~range: check if TCP window size is in given range { 0:65535 }
11.99 wscale
What: detection for TCP window scale
Type: ips_option
Usage: detect
Configuration:
• interval wscale.~range: check if TCP window scale is in given range { 0:65535 }
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12 Search Engine Modules
Search engines perform multipattern searching of packets and payload to find rules that should be evaluated. There are currently
no specific modules, although there are several search engine plugins. Related configuration is done with the basic detection
module.
13 SO Rule Modules
SO rules are dynamic rules that require custom coding to perform detection not possible with the existing rule options. These
rules typically do not have associated modules.
14 Logger Modules
All output of events and packets is done by Loggers.
14.1 alert_csv
What: output event in csv format
Type: logger
Usage: context
Configuration:
• bool alert_csv.file = false: output to alert_csv.txt instead of stdout
• multi alert_csv.fields = timestamp pkt_num proto pkt_gen pkt_len dir src_ap dst_ap rule action: selected fields will be output
in given order left to right { action | class | b64_data | dir | dst_addr | dst_ap | dst_port | eth_dst | eth_len | eth_src | eth_type |
gid | icmp_code | icmp_id | icmp_seq | icmp_type | iface | ip_id | ip_len | msg | mpls | pkt_gen | pkt_len | pkt_num | priority |
proto | rev | rule | seconds | service | sid | src_addr | src_ap | src_port | target | tcp_ack | tcp_flags | tcp_len | tcp_seq | tcp_win |
timestamp | tos | ttl | udp_len | vlan }
• int alert_csv.limit = 0: set maximum size in MB before rollover (0 is unlimited) { 0: }
• string alert_csv.separator = , : separate fields with this character sequence
14.2 alert_ex
What: output gid:sid:rev for alerts
Type: logger
Usage: context
Configuration:
• bool alert_ex.upper = false: true/false →convert to upper/lower case
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14.3 alert_fast
What: output event with brief text format
Type: logger
Usage: context
Configuration:
• bool alert_fast.file = false: output to alert_fast.txt instead of stdout
• bool alert_fast.packet = false: output packet dump with alert
• int alert_fast.limit = 0: set maximum size in MB before rollover (0 is unlimited) { 0: }
14.4 alert_full
What: output event with full packet dump
Type: logger
Usage: context
Configuration:
• bool alert_full.file = false: output to alert_full.txt instead of stdout
• int alert_full.limit = 0: set maximum size in MB before rollover (0 is unlimited) { 0: }
14.5 alert_json
What: output event in json format
Type: logger
Usage: context
Configuration:
• bool alert_json.file = false: output to alert_json.txt instead of stdout
• multi alert_json.fields = timestamp pkt_num proto pkt_gen pkt_len dir src_ap dst_ap rule action: selected fields will be output
in given order left to right { action | class | b64_data | dir | dst_addr | dst_ap | dst_port | eth_dst | eth_len | eth_src | eth_type |
gid | icmp_code | icmp_id | icmp_seq | icmp_type | iface | ip_id | ip_len | msg | mpls | pkt_gen | pkt_len | pkt_num | priority |
proto | rev | rule | seconds | service | sid | src_addr | src_ap | src_port | target | tcp_ack | tcp_flags | tcp_len | tcp_seq | tcp_win |
timestamp | tos | ttl | udp_len | vlan }
• int alert_json.limit = 0: set maximum size in MB before rollover (0 is unlimited) { 0: }
• string alert_json.separator = , : separate fields with this character sequence
14.6 alert_sfsocket
What: output event over socket
Type: logger
Usage: context
Configuration:
• string alert_sfsocket.file: name of unix socket file
• int alert_sfsocket.rules[].gid = 1: rule generator ID { 1: }
• int alert_sfsocket.rules[].sid = 1: rule signature ID { 1: }
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14.7 alert_syslog
What: output event to syslog
Type: logger
Usage: context
Configuration:
• enum alert_syslog.facility = auth: part of priority applied to each message { auth | authpriv | daemon | user | local0 | local1 |
local2 | local3 | local4 | local5 | local6 | local7 }
• enum alert_syslog.level = info: part of priority applied to each message { emerg | alert | crit | err | warning | notice | info | debug
}
• multi alert_syslog.options: used to open the syslog connection { cons | ndelay | perror | pid }
14.8 alert_unixsock
What: output event over unix socket
Type: logger
Usage: context
14.9 log_codecs
What: log protocols in packet by layer
Type: logger
Usage: context
Configuration:
• bool log_codecs.file = false: output to log_codecs.txt instead of stdout
• bool log_codecs.msg = false: include alert msg
14.10 log_hext
What: output payload suitable for daq hext
Type: logger
Usage: context
Configuration:
• bool log_hext.file = false: output to log_hext.txt instead of stdout
• bool log_hext.raw = false: output all full packets if true, else just TCP payload
• int log_hext.limit = 0: set maximum size in MB before rollover (0 is unlimited) { 0: }
• int log_hext.width = 20: set line width (0 is unlimited) { 0: }
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14.11 log_pcap
What: log packet in pcap format
Type: logger
Usage: context
Configuration:
• int log_pcap.limit = 0: set maximum size in MB before rollover (0 is unlimited) { 0: }
14.12 unified2
What: output event and packet in unified2 format file
Type: logger
Usage: context
Configuration:
• bool unified2.legacy_events = false: generate Snort 2.X style events for barnyard2 compatibility
• int unified2.limit = 0: set maximum size in MB before rollover (0 is unlimited) { 0: }
• bool unified2.nostamp = true: append file creation time to name (in Unix Epoch format)
15 DAQ Configuration and Modules
The Data AcQuisition library (DAQ), provides pluggable packet I/O. LibDAQ replaces direct calls to libraries like libpcap with
an abstraction layer that facilitates operation on a variety of hardware and software interfaces without requiring changes to Snort.
It is possible to select the DAQ module and mode when invoking Snort to perform pcap readback or inline operation, etc. The
DAQ library may be useful for other packet processing applications and the modular nature allows you to build new modules for
other platforms.
The DAQ library is provided as a separate package on the official Snort download site (https://snort.org/downloads) and contains
a number of DAQ modules including PCAP, AFPacket, NFQ, IPFQ, Netmap, and Dump implementations. Snort 3 itself contains
a few new DAQ modules mostly used for testing as described below. Additionally, DAQ modules developed by third parties to
facilitate the usage of their own hardware and software platforms exist.
15.1 Building the DAQ Library and Its Bundled DAQ Modules
Refer to the README in the LibDAQ source tarball for instructions on how to build the library and modules as well as details
on configuring and using the bundled DAQ modules.
A copy of the README from LibDAQ has been included in the Reference section of this manual for convenience. For the most
up-to-date information, please refer to the version that came with your installation’s source code.
15.2 Configuration
As with a number of features in Snort 3, the LibDAQ and DAQ module configuration may be controlled using either the command
line options or direct Snort module configuration.
DAQ modules may be statically built into Snort, but the more common case is to use DAQ modules that have been built as
dynamically loadable objects. Because of this, the first thing to take care of is informing Snort of any locations it should search
for dynamic DAQ modules. From the command line, this can be done with one or more invocations of the --daq-dir option,
Snort 3 User Manual 164 / 284
which takes a path to search as its argument. All arguments will be collected into a list of locations to be searched. In the Lua
configuration, the module_dirs property of the daq Snort module is a list of paths for the same purpose.
Next, one must select which DAQ module they wish to use by name. This is done using the --daq option from the command
line or the module property of the daq Snort module. To get a list of the available modules, run Snort with the --daq-list option
making sure to specify any DAQ module search directories beforehand. If no DAQ module is specified, Snort will default to
attempting to find and use the pcap DAQ module.
Some DAQ modules can be further directly configured using DAQ module variables. All DAQ module variables come in the
form of either just a key or a key and a value separated by an equals sign. For example, debug or fanout_type=hash. The
command line option for specifying these is --daq-var and the configuration file equivalent is the variables property of the daq
Snort module.
The LibDAQ concept of operational mode (passive, inline, or file readback) is not directly configurable but instead inferred from
other Snort configuration. The DAQ module acquisition timeout is always configured to 1 second and the packet capture length
(snaplen) is configured by the -s command line option and defaults to 1514 bytes.
Finally, and most importantly, is the input specification for the DAQ module. In readback mode, this is simply the file to be read
back and analyzed. For live traffic processing, this is the name of the interface or other necessary input specification as required
by the DAQ module to understand what to operate upon. From the command line, the -r option is used to specify a file to be read
back and the -i option is used to indicate a live interface input specification. Both are covered by the input_spec property of the
daq Snort module.
15.2.1 Command Line Example
snort --daq-dir /usr/local/lib/daq --daq-dir /opt/lib/daq --daq afpacket
--daq-var debug --daq-var fanout_type=hash -i eth1:eth2
15.2.2 Configuration File Example
The following is the equivalent of the above command line DAQ configuration in Lua form:
daq =
{
module_dirs =
{
’/usr/local/lib/daq’,
’/opt/lib/daq’
},
module = ’afpacket’,
input_spec = ’eth1:eth2’,
variables =
{
’debug’,
’fanout_type=hash’
}
}
15.2.3 Interaction With Multiple Packet Threads
DAQ configuration can become much more complicated as additional packet threads are introduced. To allow for more flexibility
in configuring DAQ module instances, each packet thread can be configured with its own input specification and/or DAQ module
variables, which creates two classes of each: instance-specific and global. Global DAQ module variables are those defined before
any -i option on the command line or in the top-level variables property demonstrated in the previous section. The global input
specification is defined by either the first -i option on the command line (which doubles as the input specification for instance 0)
or the top-level input_spec in the i’daq’ Snort module. Instance-specific input specifiers are configured on the command line by
Snort 3 User Manual 165 / 284
giving multiple -i options. In the same way, instance-specific DAQ module variables on the command line are declared normally
but follow and apply only to the instance operating on the last -i option. When configuring through Lua, the instances property
of the daq Snort module is a list of tables, each defining instance-specific configuration for a given instance ID.
Each packet thread will create an instance of the chosen DAQ module using the global interface specification and global set of
DAQ module variables unless they were overridden with instance-specific values. When DAQ module instances are configured,
any global DAQ modules will be set and then any instance-specific DAQ variables. This means that an instance will "inherit" the
global DAQ modules and can override those by specifying them again with different values or add to them by specifying new
variables entirely.
Here is the configuration for a hypothetical AFPacket DAQ module that has been modified to loadbalance based on DAQ variables
(lb_total is the total number of instances to loadbalance across and is set globally, and lb_id is the instance’s loadbalancing ID
within that total and is set per-instance) across 4 packet processing threads within Snort:
daq =
{
module_dirs =
{
’/usr/local/sf/lib/daq’
},
module = ’afpacket’,
input_spec = ’eth1’,
variables =
{
’lb_total=4’
},
instances =
{
{
id = 0,
variables =
{
’lb_id=1’,
}
},
{
id = 1,
variables =
{
’lb_id=2’,
}
},
{
id = 2,
variables =
{
’lb_id=3’,
}
},
{
id = 3,
variables =
{
’lb_id=4’,
}
},
}
}
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The equivalent command line invocation would look like this (made uglier by the lack of needing a different input specification
for each thread):
snort --daq-dir /usr/local/sf/lib/daq --daq afpacket --daq-var lb_total=4 -i
eth1 --daq-var lb_id=1 -i eth1 --daq-var lb_id=2 -i eth1 --daq-var lb_id=3 -i
eth1 --daq-var lb_id=4 -z 4
For any particularly complicated setup, it is recommended that one configure via a Lua configuration file rather than using the
command line options.
15.3 DAQ Modules Included With Snort 3
15.3.1 Socket Module
The socket module provides provides a stream socket server that will accept up to 2 simultaneous connections and bridge them
together while also passing data to Snort for inspection. The first connection accepted is considered the client and the second
connection accepted is considered the server. If there is only one connection, stream data can’t be forwarded but it is still
inspected.
Each read from a socket of up to snaplen bytes is passed as a packet to Snort along with a DAQ_SktHdr_t pointer in DAQ_PktHdr_t→priv_ptr.
DAQ_SktHdr_t conveys IP4 address, ports, protocol, and direction. Socket packets can be configured to be TCP or UDP. The
socket DAQ can be operated in inline mode and is able to block packets.
The socket DAQ uses DLT_SOCKET and requires that Snort load the socket codec which is included in the extra package.
To use the socket DAQ, start Snort like this:
./snort --plugin-path /path/to/lib/snort_extra \
--daq socket [--daq-var port=<port>] [--daq-var proto=<proto>] [-Q]
<port> ::= 1..65535; default is 8000
<proto> ::= tcp | udp
• This module only supports ip4 traffic.
• This module is only supported by Snort 3. It is not compatible with Snort 2.
• This module is primarily for development and test.
15.3.2 File Module
The file module provides the ability to process files directly w/o having to extract them from pcaps. Use the file module with
Snort’s stream_file to get file type identification and signature services. The usual IPS detection and logging etc. is available too.
You can process all the files in a directory recursively using 8 threads with these Snort options:
--pcap-dir path -z 8
• This module is only supported by Snort 3. It is not compatible with Snort 2.
• This module is primarily for development and test.
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15.3.3 Hext Module
The hext module generates packets suitable for processing by Snort from hex/plain text. Raw packets include full headers and are
processed normally. Otherwise the packets contain only payload and are accompanied with flow information (4-tuple) suitable
for processing by stream_user.
The first character of the line determines it’s purpose:
’$’ command
’#’ comment
’"’ quoted string packet data
’x’ hex packet data
’ ’ empty line separates packets
The available commands are:
$client <ip4> <port>
$server <ip4> <port>
$packet -> client
$packet -> server
$packet <addr> <port> -> <addr> <port>
Client and server are determined as follows. $packet →client indicates to the client (from server) and $packet →server indicates
a packet to the server (from client). $packet followed by a 4-tuple uses the heuristic that the client is the side with the lower port
number.
The default client and server are 192.168.1.1 12345 and 10.1.2.3 80 respectively. $packet commands with a 4-tuple do not change
client and server set with the other $packet commands.
$packet commands should be followed by packet data, which may contain any combination of hex and strings. Data for a packet
ends with the next command or a blank line. Data after a blank line will start another packet with the same tuple as the prior one.
Strings may contain the following escape sequences:
\r = 0x0D = carriage return
\n = 0x0A = new line
\t = 0x09 = tab
\\ = 0x5C = \
Format your input carefully; there is minimal error checking and little tolerance for arbitrary whitespace. You can use Snort’s -L
hext option to generate hext input from a pcap.
• This module only supports ip4 traffic.
• This module is only supported by Snort 3. It is not compatible with Snort 2.
• This module is primarily for development and test.
The hext DAQ also supports a raw mode which is activated by setting the data link type. For example, you can input full ethernet
packets with --daq-var dlt=1 (Data link types are defined in the DAQ include sfbpf_dlt.h.) Combine that with the hext logger in
raw mode for a quick (and dirty) way to edit pcaps. With --lua "log_hext = { raw = true }", the hext logger will dump the full
packet in a way that can be read by the hext DAQ in raw mode. Here is an example:
# 3 [96]
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x02 09 08 07 06 05 02 01 02 03 04 05 08 00 45 00 00 52 00 03 # ..............E..R ←-
..
x00 00 40 06 5C 90 0A 01 02 03 0A 09 08 07 BD EC 00 50 00 00 # ..@.\............P ←-
..
x00 02 00 00 00 02 50 10 20 00 8A E1 00 00 47 45 54 20 2F 74 # ......P. .....GET ←-
/t
x72 69 67 67 65 72 2F 31 20 48 54 54 50 2F 31 2E 31 0D 0A 48 # rigger/1 HTTP ←-
/1.1..H
x6F 73 74 3A 20 6C 6F 63 61 6C 68 6F 73 74 0D 0A # ost: localhost..
A comment indicating packet number and size precedes each packet dump. Note that the commands are not applicable in raw
mode and have no effect.
16 Snort 3 vs Snort 2
Snort 3 differs from Snort 2 in the following ways:
• command line and conf file syntax made more uniform
• removed unused and deprecated features
• remove as many barriers to successful run as possible (e.g.: no upper bounds on memcaps)
• assume the simplest mode of operation (e.g.: never assume input from or output to some hardcoded filename)
• all Snort 2 config options are grouped into Snort 3 modules
16.1 Features New to Snort 3
Some things Snort++ can do today that Snort can not do:
• regex fast patterns, not just literals
• FlatBuffers and JSON perf monitor logs
• LuaJIT scriptable rule options and loggers
• pub/sub inspection events (currently used by sip and http_inspect to appid)
• JIT buffer stuffers (notably with new http_inspect)
• C-style comments in rules
• #begin . . . #end comment blocks in rules
• rule remarks (comment is part of rule, not just in it)
• process raw files (eg read a PDF and do file processing)
• process raw payload (eg bridge 2 sockets and do inspection)
• fast pattern offload to separate thread (experimental)
• track all memory allocated
• add or override any config item on command line
• set CPU affinity
• pause and resume commands
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16.2 Features Improved over Snort 2
Some things Snort++ can do today that Snort can not do as well:
• Hyperscan search engine plugin (Intel provides patch for Snort 2)
• fast pattern sensitive data (Snort 2 requires a slow, extra search)
• multiple packet threads with one config (Snort 2 requires multiple processes)
• wizard automatically detects service for first flow (Snort 2 appid detects for next flow)
• nested policy binding (Snort 2 has just one level)
• decode arbitrary layers (Snort 2 supports only 2 IP layers)
• process PDU buffers (Snort 2 only processes packets)
• fully stateful http_inspect with 97 builtin alerts (Snort 2 is only partly stateful with 33 builtin alerts)
• output all semantic errors before quitting (Snort 2 stops at first one)
• alert file rules (Snort 2 must use multiple rules)
• alert service rules, eg alert http (Snort 2 must use metadata:service)
• automatic fast_pattern only (Snort 2 requires explicit fast_pattern:only)
• elided rule headers omit nets and/or ports (Snort 2 requires explicit any)
• dump builtin rule stubs (Snort 2 can only dump SO stubs)
• rule sticky buffers (Snort 2 buffers must be repeated)
• http_header:name supported to restrict to single field (Snort 2 searches all headers)
• fully equivalent SO rules (Snort 2 has some limitations with SO processing)
• text-based SO rule implementation (Snort 2 requires tedious, nested C structs)
• extensible module-based tracing (Snort 2 has a fixed set of flags)
• over 200 plugins, no need to change core source code (Snort 2 only supports preprocessors and outputs)
• use consistent conf syntax (Snort 2 defines lists different ways in different places, etc.)
• use consistent rule syntax (Snort 2 has semicolon separated suboptions, etc.)
• arbitrary whitespace and comments in conf and rules (Snort 2 requires newline escapes)
• properly parse rules (Snort 2 can actually completely ignore stuff)
• optional, expanded warnings output, can be fatal (Snort 2 warnings limited and are not optional or fatal)
• define and use arbitrary variables and functions in config with Lua (Snort 2 has variables just for rule headers)
• text-based command line shell (Snort 2 has binary control socket)
• generate text and HTML user guide in addition to PDF (Snort 2 just has PDF and Talos provides HTML)
• generate developer’s guide (Snort 2’s is manually written)
• extensive command line help, eg every config item, rule option, and peg count (Snort 2 only has command line args)
• cmake builds (Snort 2 only does automake)
• read rules from separate file or stdin (Snort 2 requires rules directly in or included in conf)
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• simple, clean, uniform startup and shutdown output (Snort 2 is heavy and inconsistent)
• port_scan is fully configurable (Snort 2 hard codes most of the configuration)
• port_scan can block scans (Snort 2 can only detect scans)
• sigquit will cause a --dirty-pig style exit (Snort 2 handles sigquit the same as sigterm and sigint)
• detection trace (Snort 2 has more limited buffer dumping)
• updated unified2 events with MPLS, VLAN, and IP6 (Snort 2 requires configuration and extra data)
• significantly more unit tests, including --catch and make check (Snort 2 has very few unit tests)
• better modularity 346K/1534 = 226 lines/file, max=2700 (Snort 2 has 440K/1021 = 431 lines/file, max=13K)
16.3 Build Options
• configure --with-lib{pcap,pcre}-* →--with-{pcap,pcre}-*
• control socket, cs_dir, and users were deleted
• POLICY_BY_ID_ONLY code was deleted
• hardened --enable-inline-init-failopen / INLINE_FAILOPEN
16.4 Command Line
• --pause loads config and waits for resume before processing packets
• --require-rule-sid is hardened
• --shell enables interactive Lua shell
• -T is assumed if no input given
• added --help-config prefix to dump all matching settings
• added --script-path
• added -L none|dump|pcap
• added -z <#> and --max-packet-threads <#>
• delete --enable-mpls-multicast, --enable-mpls-overlapping-ip, --max-mpls-labelchain-len, --mpls-payload-type
• deleted --pid-path and --no-interface-pidfile
• deleting command line options which will be available with --lua or some such including: -I, -h, -F, -p, --disable-inline-init-
failopen
• hardened -n < 0
• removed --search-method
• replaced "unknown args are bpf" with --bpf
• replaced --dynamic-*-lib[-dir] with --plugin-path (with : separators)
• removed -b, -N, -Z and, --perfmon-file options
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16.5 Conf File
• Snort 3 has a default unicode.map
• Snort 3 will not enforce an upper bound on memcaps and the like within 64 bits
• Snort 3 will supply a default *_global config if not specified (Snort 2 would fatal; e.g. http_inspect_server w/o http_inspect_global)
• address list syntax changes: [[ and ]] must be [ [ and ] ] to avoid Lua string parsing errors (unless in quoted string)
• because the Lua conf is live code, we lose file:line locations in app error messages (syntax errors from Lua have file:line)
• changed search-method names for consistency
• delete config include_vlan_in_alerts (not used in code)
• delete config so_rule_memcap (not used in code)
• deleted --disable-attribute-table-reload-thread
• deleted config decode_*_{alerts,drops} (use rules only)
• deleted config dump-dynamic-rules-path
• deleted config ipv6_frag (not actually used)
• deleted config threshold and ips rule threshold (→event_filter)
• eliminated ac-split; must use ac-full-q split-any-any
• frag3 →defrag, arpspoof →arp_spoof, sfportscan →port_scan, perfmonitor →perf_monitor, bo →back_orifice
• limits like "1234K" are now "limit = 1234, units = K"
• lua field names are (lower) case sensitive; snort.conf largely wasn’t
• module filenames are not configurable: always <log-dir>/<module-name><suffix> (suffix is determined by module)
• no positional parameters; all name = value
• perf_monitor configuration was simplified
• portscan.detect_ack_scans deleted (exact same as include_midstream)
• removed various run modes - now just one
• frag3 default policy is Linux not bsd
• lowmem* search methods are now in snort_examples
• deleted unused http_inspect stateful mode
• deleted stateless inspection from ftp and telnet
• deleted http and ftp alert options (now strictly rule based)
• preprocessor disabled settings deleted since no longer relevant
• sessions are always created; snort config stateful checks eliminated
• stream5_tcp: prune_log_max deleted; to be replaced with histogram
• stream5_tcp: max_active_responses, min_response_seconds moved to active.max_responses, min_interval
Snort 3 User Manual 172 / 284
16.6 Rules
• all rules must have a sid
• sid == 0 not allowed
• deleted activate / dynamic rules
• deleted unused rule_state.action
• deleted metadata engine shared
• deleted metadata: rule-flushing (with PDU flushing rule flushing can cause missed attacks, the opposite of its intent)
• changed metadata:service one[, service two]; to service:one[, two];
• soid is now a non-metadata option
• metadata is now truly metadata with no impact on detection (Snort doesn’t care about metadata internal structure / syntax)
• deleted fast_pattern:only; use fast_pattern, nocase (option is not added to detection tree if not required)
• changed fast_pattern:<offset>,<length> to fastpattern_offset: <offset>, fast_pattern_length <length>
• fast pattern sensitive data with sd_pattern using hyperscan
• hyperscan regex fast patterns with regex:"<regex>", fast_pattern;
• no ; separated content suboptions
• offset, depth, distance, and within must use a space separator not colon (e.g. offset:5; becomes offset 5;)
• content suboptions http_* are now full options
• added sticky buffers: buffer selector options must precede contents and remain in effect until changed
• the following pcre options have been deleted: use sticky buffers instead B, U, P, H, M, C, I, D, K, S, Y
• deleted uricontent option; use sticky buffer uricontent:"foo" -→http_uri; content:"foo"
• deleted urilen raw and norm; must use http_raw_uri and http_uri instead
• deleted unused http_encode option
• urilen replaced with generic bufferlen which applies to current sticky buffer
• added optional selector to http_header, e.g. http_header:User-Agent;
• the all new http_inspect has new buffers and rule options
• added alert file and alert service rules (service in body not required if there is only one and it is in header; alert service / file
rules disable fast pattern searching of raw packets)
• rule option sequence: <stub> soid <hidden>
• arbitrary whitespace and multiline rules w/o \n
• #begin . . . #end comments to easily comment out multiple lines
• add rule remarks option with rem:"arbitrary comment"
• nets and/or ports may be omitted from rule headers (matches any)
• parse all rules and output all errors before quitting
• read rules from conf, separate rules file, or stdin
Snort 3 User Manual 173 / 284
16.7 Output
• alert_fast includes packet data by default
• all text mode outputs default to stdout
• changed default logging mode to -L none
• deleted layer2resets and flexresp2_*
• deleted log_ascii
• general output guideline: don’t print zero counts
• Snort 3 queues decoder and inspector events to the main event queue before ips policy is selected; since some events may not
be enabled, the queue needs to be sized larger than with Snort 2 which used an intermediate queue for decoder events.
• deleted the intermediate http and ftp_telnet event queues
• alert_unified2 and log_unified2 have been deleted
16.8 Sensitive Data
The Snort 2.X SDF Preprocessor is gone, replaced by ips option sd_pattern. The sd_pattern rule option is synonymous with
the sd_pattern option used for gid:138 rules, but has a different syntax. A major difference in syntax is the use of Hyperscan
pattern matching library which provides a regex language similar to PCRE.
To facilitate continued performance, sd_pattern rule option is implemented with Hyperscan pattern matching library. The rule
option is now also utilized as a "fast pattern" in the Snort engine which provides a significant performance improvement over the
separate detection step of earlier implementations.
The preprocessor alert SDF_COMBO_ALERT (139:1) has been removed and has no replacement in Snort 3.X. This is because
the rule offered no additional value over gid:138 rules and was difficult to interpret the result of.
For more information, See Features > Sensitive Data Filtering for details.
17 Snort2Lua
One of the major differences between Snort 2 and Snort 3 is the configuration. Snort 2 configuration files are written in Snort-
specific syntax while Snort 3 configuration files are written in Lua. Snort2Lua is a program specifically designed to convert valid
Snort 2 configuration files into Lua files that Snort 3 can understand.
Snort2Lua reads your legacy Snort conf file(s) and generates Snort 3 Lua and rules files. When running this program, the only
mandatory option is to provide Snort2Lua with a Snort 2 configuration file. The default output file file is snort.lua, the default
error file will be snort.rej, and the default rule file is the output file (default is snort.lua). When Snort2Lua finishes running,
the resulting configuration file can be successfully run as the Snort3.0 configuration file. The sole exception to this rule is
when Snort2Lua cannot find an included file. If that occurs, the file will still be included in the output file and you will need
to manually adjust or comment the file name. Additionally, if the exit code is not zero, some of the information may not be
successfully converted. Check the error file for all of the conversion problems.
Those errors can occur for a multitude of reasons and are not necessarily bad. Snort2Lua expects a valid Snort 2 configuration.
Therefore, if the configuration is invalid or has questionable syntax, Snort2Lua may fail to parse the configuration file or create
an invalid Snort 3 configuration file.
There are a also few peculiarities of Snort2Lua that may be confusing to a first time user:
• Aside from an initial configuration file (which is specified from the command line or as the file in ‘config binding’), every file
that is included into Snort 3 must be either a Lua file or a rule file; the file cannot contain both rules and Lua syntax. Therefore,
when parsing a file specified with the ‘include’ command, Snort2Lua will output both a Lua file and a rule file.
Snort 3 User Manual 174 / 284
• Any line that is a comment in a configuration file will be added in to a comments section at the bottom of the main configuration
file.
• Rules that contain unsupported options will be converted to the best of Snort2Lua’s capability and then printed as a comment
in the rule file.
• Files with a .rules suffix are assumed to be Talos 2.X rules files and converted line-by-line. In this case, lines starting with
alert are converted as usual but lines starting with # alert are assumed to be commented out rules which are converted to 3.0
format and remain comments in the output file. All other comments are passed through directly. There is no support for other
commented rule actions since these do not appear in Talos rules files.
17.1 Snort2Lua Command Line
By default, Snort2Lua will attempt to parse every ‘include’ file and every ‘binding’ file. There is an option to change this
functionality.
When specifying a rule file with one of the command line options, Snort2Lua will output all of the converted rules to that specified
rule file. This is especially useful when you are only interesting in converting rules since there is no Lua syntax in rule files.
There is also an option that tells Snort2Lua to output every rule for a given configuration into a single rule file. Similarly, there
is an option pull all of the Lua syntax from every ‘include’ file into the output file.
There are currently three output modes: default, quiet, and differences. As expected, quiet mode produces a Snort configuration.
All errors (aside from Fatal Snort2Lua errors), differences, and comments will omitted from the final output file. Default mode
will print everything. That mean you will be able to see exactly what changes have occurred between Snort 2 and Snort 3 in
addition to the new syntax, the original file’s comments, and all errors that have occurred. Finally, differences mode will not
actually output a valid Snort 3 configuration. Instead, you can see the exact options from the input configuration that have
changed.
17.1.1 Usage: snort2lua [OPTIONS]. . . -c <snort_conf> . . .
Converts the Snort configuration file specified by the -c or --conf-file options into a Snort++ configuration file
Options:
•-? show usage
•-h this overview of snort2lua
•-a default option. print all data
•-c <snort_conf> The Snort <snort_conf> file to convert
•-d print the differences, and only the differences, between the Snort and Snort++ configurations to the <out_file>
•-e <error_file> output all errors to <error_file>
•-i if <snort_conf> file contains any <include_file> or <policy_file> (i.e. include path/to/conf/other_conf ), do NOT parse those
files
•-m add a remark to the end of every converted rule
•-o <out_file> output the new Snort++ lua configuration to <out_file>
•-q quiet mode. Only output valid configuration information to the <out_file>
•-r <rule_file> output any converted rule to <rule_file>
•-s when parsing <include_file>, write <include_file>’s rules to <rule_file>. Meaningless if -i provided
•-t when parsing <include_file>, write <include_file>’s information, excluding rules, to <out_file>. Meaningless if -i provided
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•-V Print the current Snort2Lua version
•--bind-wizard Add default wizard to bindings
•--conf-file Same as -c. A Snort <snort_conf> file which will be converted
•--dont-parse-includes Same as -p. if <snort_conf> file contains any <include_file> or <policy_file> (i.e. include path/to/con-
f/other_conf ), do NOT parse those files
•--error-file=<error_file> Same as -e. output all errors to <error_file>
•--help Same as -h. this overview of snort2lua
•--ips-policy-pattern Convert config bindings matching this path to ips policy bindings
•--markup print help in asciidoc compatible format
•--output-file=<out_file> Same as -o. output the new Snort++ lua configuration to <out_file>
•--print-all Same as -a. default option. print all data
•--print-binding-order Print sorting priority used when generating binder table
•--print-differences Same as -d. output the differences, and only the differences, between the Snort and Snort++ configurations
to the <out_file>
•--quiet Same as -q. quiet mode. Only output valid configuration information to the <out_file>
•--remark same as -m. add a remark to the end of every converted rule
•--rule-file=<rule_file> Same as -r. output any converted rule to <rule_file>
•--single-conf-file Same as -t. when parsing <include_file>, write <include_file>’s information, excluding rules, to <out_file>
•--single-rule-file Same as -s. when parsing <include_file>, write <include_file>’s rules to <rule_file>.
•--version Same as -V. Print the current Snort2Lua version
Required option:
• A Snort configuration file to convert. Set with either -c or --conf-file
Default values:
• <out_file> = snort.lua
• <rule_file> = <out_file> = snort.lua. Rules are written to the local_rules variable in the <out_file>
• <error_file> = snort.rej. This file will not be created in quiet mode.
17.2 Known Problems
• Any Snort 2 ‘string’ which is dependent on a variable will no longer have that variable in the Lua string.
• Snort2Lua currently does not handle variables well. First, that means variables will not always be parsed correctly. Second,
sometimes a variables value will be output in the lua file rather than a variable For instance, if Snort2Lua attempted to convert
the line include $RULE_PATH/example.rule, the output may output include /etc/rules/example.rule instead.
• When Snort2Lua parses a ‘binding’ configuration file, the rules and configuration will automatically be combined into the
same file. Also, the new files name will automatically become the old file’s name with a .lua extension. There is currently no
way to specify or change that files name.
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• If a rule’s action is a custom ruletype, that rule action will be silently converted to the rultype’s type. No warnings or errors are
currently emitted. Additionally, the custom ruletypes outputs will be silently discarded.
• If the original configuration contains a binding that points to another file and the binding file contains an error, Snort2Lua will
output the number of rejects for the binding file in addition to the number of rejects in the main file. The two numbers will
eventually be combined into one output.
17.3 Usage
Snort2Lua is included in the Snort 3 distribution. The Snort2Lua source code is located in the tools/snort2lua directory. The
program is automatically built and installed.
Translating your configuration
To run Snort2Lua, the only requirement is a file containing Snort 2 syntax. Assuming your configuration file is named snort.conf,
run the command
snort2lua -c snort.conf
Snort2Lua will output a file named snort.lua. Assuming your snort.conf file is a valid Snort 2 configuration file, than the resulting
snort.lua file will always be a valid Snort 3 configuration file; any errors that occur are because Snort 3 currently does not support
all of the Snort 2 options.
Every keyword from the Snort configuration can be found in the output file. If the option or keyword has changed, then a
comment containing both the option or keyword’s old name and new name will be present in the output file.
Translating a rule file
Snort2Lua can also accommodate translating individual rule files. Assuming the Snort 2 rule file is named snort.rules and you
want the new rule file to be name updated.rules, run the command
snort2lua -c snort.rules -r updated.rules
Snort2Lua will output a file named updated.rules. That file, updated.rules, will always be a valid Snort 3 rule file. Any rule that
contains unsupported options will be a comment in the output file.
Understanding the Output
Although Snort2Lua outputs very little to the console, there are several things that occur when Snort2Lua runs. This is a list of
Snort2Lua outputs.
The console. Every line that Snort2Lua is unable to translate from the Snort 2.X format to the Snort 3 format is considered an
error. Upon exiting, Snort2Lua will print the number of errors that occurred. Snort2Lua will also print the name of the error file.
The output file. As previously mentioned, Snort2Lua will create a Lua file with valid Snort 3 syntax. The default Lua file is
named snort.lua. This file is the equivalent of your main Snort 2 configuration file.
The rule file. By default, all rules will be printed to the Lua file. However, if a rule file is specified on the command line, any
rules found in the Snort 2 configuration will be written to the rule file instead
The error file. By default, the error file is snort.rej. It will only be created if errors exist. Every error referenced on the command
line can be found in this file. There are two reasons an error can occur.
• The Snort 2 configuration file has invalid syntax. If Snort 2 cannot parse the configuration file, neither can Snort2Lua. In the
example below, Snort2Lua could not convert the line config bad_option. Since that is not valid Snort 2 syntax, this is a syntax
error.
• The Snort 2 configuration file contains preprocessors and rule options that are not supported in Snort 3. If Snort 2 can parse
a line that Snort2Lua cannot parse, than Snort 3 does not support something in the line. As Snort 3 begins supporting these
preprocessors and rule options, Snort2Lua will also begin translating these lines. One example of such an error is dcerpc2.
Additional .lua and .rules files. Every time Snort2Lua parses the include or binding keyword, the program will attempt to parse
the file referenced by the keyword. Snort2Lua will then create one or two new files. The new files will have a .lua or .rules
extension appended to the original filename.
Snort 3 User Manual 177 / 284
18 Extending Snort
18.1 Plugins
Plugins have an associated API defined for each type, all of which share a common header, called the BaseApi. A dynamic
library makes its plugins available by exporting the snort_plugins symbol, which is a null terminated array of BaseApi pointers.
The BaseApi includes type, name, API version, plugin version, and function pointers for constructing and destructing a Module.
The specific API add various other data and functions for their given roles.
18.2 Modules
If we are defining a new Inspector called, say, gadget, it might be configured in snort.lua like this:
gadget =
{
brain = true,
claw = 3
}
When the gadget table is processed, Snort will look for a module called gadget. If that Module has an associated API, it will be
used to configure a new instance of the plugin. In this case, a GadgetModule would be instantiated, brain and claw would be set,
and the Module instance would be passed to the GadgetInspector constructor.
Module has three key virtual methods:
•begin() - called when Snort starts processing the associated Lua table. This is a good place to allocate any required data and
set defaults.
•set() - called to set each parameter after validation.
•end() - called when Snort finishes processing the associated Lua table. This is where additional integrity checks of related
parameters should be done.
The configured Module is passed to the plugin constructor which pulls the configuration data from the Module. For non-trivial
configurations, the working paradigm is that Module hands a pointer to the configured data to the plugin instance which takes
ownership.
Note that there is at most one instance of a given Module, even if multiple plugin instances are created which use that Module.
(Multiple instances require Snort binding configuration.)
18.3 Inspectors
There are several types of inspector, which determines which inspectors are executed when:
• IT_BINDER - determines which inspectors apply to given flows
• IT_WIZARD - determines which service inspector to use if none explicitly bound
• IT_PACKET - used to process all packets before session and service processing (e.g. normalize)
• IT_NETWORK - processes packets w/o service (e.g. arp_spoof, back_orifice)
• IT_STREAM - for flow tracking, ip defrag, and tcp reassembly
• IT_SERVICE - for http, ftp, telnet, etc.
• IT_PROBE - process all packets after all the above (e.g. perf_monitor, port_scan)
Snort 3 User Manual 178 / 284
18.4 Codecs
The Snort Codecs decipher raw packets. These Codecs are now completely pluggable; almost every Snort Codec can be built
dynamically and replaced with an alternative, customized Codec. The pluggable nature has also made it easier to build new
Codecs for protocols without having to touch the Snort code base.
The first step in creating a Codec is defining its class and protocol. Every Codec must inherit from the Snort Codec class defined
in "framework/codec.h". The following is an example Codec named "example" and has an associated struct that is 14 bytes long.
#include <cstdint>
#include <arpa/inet.h>
#include “framework/codec.h”
#include "main/snort_types.h"
#define EX_NAME “example”
#define EX_HELP “example codec help string”
struct Example
{
uint8_t dst[6];
uint8_t src[6];
uint16_t ethertype;
static inline uint8_t size()
{ return 14; }
}
class ExCodec : public Codec
{
public:
ExCodec() : Codec(EX_NAME) { }
~ExCodec() { }
bool decode(const RawData&, CodecData&, DecodeData&) override;
void get_protocol_ids(std::vector<uint16_t>&) override;
};
After defining ExCodec, the next step is adding the Codec’s decode functionality. The function below does this by implementing
a valid decode function. The first parameter, which is the RawData struct, provides both a pointer to the raw data that has come
from a wire and the length of that raw data. The function takes this information and validates that there are enough bytes for
this protocol. If the raw data’s length is less than 14 bytes, the function returns false and Snort discards the packet; the packet
is neither inspected nor processed. If the length is greater than 14 bytes, the function populates two fields in the CodecData
struct, next_prot_id and lyr_len. The lyr_len field tells Snort the number of bytes that this layer contains. The next_prot_id field
provides Snort the value of the next EtherType or IP protocol number.
bool ExCodec::decode(const RawData& raw, CodecData& codec, DecodeData&)
{
if ( raw.len < Example::size() )
return false;
const Example*const ex = reinterpret_cast<const Example*>(raw.data);
codec.next_prot_id = ntohs(ex->ethertype);
codec.lyr_len = ex->size();
return true;
}
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For instance, assume this decode function receives the following raw data with a validated length of 32 bytes:
00 11 22 33 44 55 66 77 88 99 aa bb 08 00 45 00
00 38 00 01 00 00 40 06 5c ac 0a 01 02 03 0a 09
The Example struct’s EtherType field is the 13 and 14 bytes. Therefore, this function tells Snort that the next protocol has an
EtherType of 0x0800. Additionally, since the lyr_len is set to 14, Snort knows that the next protocol begins 14 bytes after the
beginning of this protocol. The Codec with EtherType 0x0800, which happens to be the IPv4 Codec, will receive the following
data with a validated length of 18 ( == 32 – 14):
45 00 00 38 00 01 00 00 40 06 5c ac 0a 01 02 03
0a 09
How does Snort know that the IPv4 Codec has an EtherType of 0x0800? The Codec class has a second virtual function named
get_protocol_ids(). When implementing the function, a Codec can register for any number of values between 0x0000 - 0xFFFF.
Then, if the next_proto_id is set to a value for which this Codec has registered, this Codec’s decode function will be called. As
a general note, the protocol ids between [0, 0x00FF] are IP protocol numbers, [0x0100, 0x05FF] are custom types, and [0x0600,
0xFFFF] are EtherTypes.
For example, in the get_protocol_ids function below, the ExCodec registers for the protocols numbers 17, 787, and 2054. 17
happens to be the protocol number for UDP while 2054 is ARP’s EtherType. Therefore, this Codec will now attempt to decode
UDP and ARP data. Additionally, if any Codec sets the next_protocol_id to 787, ExCodec’s decode function will be called.
Some custom protocols are already defined in the file "protocols/protocol_ids.h"
void ExCodec::get_protocol_ids(std::vector<uint16_t>&v)
{
v.push_back(0x0011); // == 17 == UDP
v.push_back(0x1313); // == 787 == custom
v.push_back(0x0806); // == 2054 == ARP
}
To register a Codec for Data Link Type’s rather than protocols, the function get_data_link_type() can be similarly implemented.
The final step to creating a pluggable Codec is the snort_plugins array. This array is important because when Snort loads a
dynamic library, the program only find plugins that are inside the snort_plugins array. In other words, if a plugin has not been
added to the snort_plugins array, that plugin will not be loaded into Snort.
Although the details will not be covered in this post, the following code snippet is a basic CodecApi that Snort can load. This
snippet can be copied and used with only three minor changes. First, in the function ctor, ExCodec should be replaced with the
name of the Codec that is being built. Second, EX_NAME must match the Codec’s name or Snort will be unable to load this
Codec. Third, EX_HELP should be replaced with the general description of this Codec. Once this code snippet has been added,
ExCodec is ready to be compiled and plugged into Snort.
static Codec*ctor(Module*)
{ return new ExCodec; }
static void dtor(Codec *cd)
{ delete cd; }
static const CodecApi ex_api =
{
{
PT_CODEC,
EX_NAME,
EX_HELP,
CDAPI_PLUGIN_V0,
0,
nullptr,
nullptr,
Snort 3 User Manual 180 / 284
},
nullptr, // pointer to a function called during Snort’s startup.
nullptr, // pointer to a function called during Snort’s exit.
nullptr, // pointer to a function called during thread’s startup.
nullptr, // pointer to a function called during thread’s destruction.
ctor, // pointer to the codec constructor.
dtor, // pointer to the codec destructor.
};
SO_PUBLIC const BaseApi*snort_plugins[] =
{
&ex_api.base,
nullptr
};
Two example Codecs are available in the extra directory on git and the extra tarball on the Snort page. One of those examples is
the Token Ring Codec while the other example is the PIM Codec.
As a final note, there are four more virtual functions that a Codec should implement: encode, format, update, and log. If the
functions are not implemented Snort will not throw any errors. However, Snort may also be unable to accomplish some of its
basic functionality.
• encode is called whenever Snort actively responds and needs to builds a packet, i.e. whenever a rule using an IPS ACTION
like react, reject, or rewrite is triggered. This function is used to build the response packet protocol by protocol.
• format is called when Snort is rebuilding a packet. For instance, every time Snort reassembles a TCP stream or IP fragment,
format is called. Generally, this function either swaps any source and destination fields in the protocol or does nothing.
• update is similar to format in that it is called when Snort is reassembling a packet. Unlike format, this function only sets length
fields.
• log is called when either the log_codecs logger or a custom logger that calls PacketManager::log_protocols is used when
running Snort.
18.5 IPS Actions
Action plugins specify a builtin action in the API which is used to determine verdict. (Conversely, builtin actions don’t have an
associated plugin function.)
18.6 Developers Guide
Run doc/dev_guide.sh to generate /tmp/dev_guide.html, an annotated guide to the source tree.
18.7 Piglet Test Harness
In order to assist with plugin development, an experimental mode called "piglet" mode is provided. With piglet mode, you can
call individual methods for a specific plugin. The piglet tests are specified as Lua scripts. Each piglet test script defines a test for
a specific plugin.
Here is a minimal example of a piglet test script for the IPv4 Codec plugin:
plugin =
{
type = "piglet",
name = "codec::ipv4",
use_defaults = true,
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test = function()
local daq_header = DAQHeader.new()
local raw_buffer = RawBuffer.new("some data")
local codec_data = CodecData.new()
local decode_data = DecodeData.new()
return Codec.decode(
daq_header,
raw_buffer,
codec_data,
decode_data
)
end
}
To run snort in piglet mode, first build snort with the ENABLE_PIGLET option turned on (pass the flag -DENABLE_PIGLET:BOOL=ON
in cmake).
Then, run the following command:
snort --script-path $test_scripts --piglet
(where $test_scripts is the directory containing your piglet tests).
The test runner will generate a check-like output, indicating the the results of each test script.
18.8 Piglet Lua API
This section documents the API that piglet exposes to Lua. Refer to the piglet directory in the source tree for examples of usage.
Note: Because of the differences between the Lua and C++ data model and type system, not all parameters map directly to the
parameters of the underlying C\++ member functions. Every effort has been made to keep the mappings consist, but there are
still some differences. They are documented below.
18.8.1 Plugin Instances
For each test, piglet instantiates plugin specified in the name field of the plugin table. The virtual methods of the instance are
exposed in a table unique to each plugin type. The name of the table is the CamelCase name of the plugin type.
For example, codec plugins have a virtual method called decode. This method is called like this:
Codec.decode(...)
Codec
•Codec.get_data_link_type() →{ int, int, ... }
•Codec.get_protocol_ids() →{ int, int, ... }
•Codec.decode(DAQHeader, RawBuffer, CodecData, DecodeData) →bool
•Codec.log(RawBuffer, uint[lyr_len])
•Codec.encode(RawBuffer, EncState, Buffer) →bool
•Codec.update(uint[flags_hi], uint[flags_lo], RawBuffer, uint[lyr_len] →int
•Codec.format(bool[reverse], RawBuffer, DecodeData)
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Differences:
• In Codec.update(), the (uint64_t) flags parameter has been split into flags_hi and flags_lo
Inspector
•Inspector.configure()
•Inspector.tinit()
•Inspector.tterm()
•Inspector.likes(Packet)
•Inspector.eval(Packet)
•Inspector.clear(Packet)
•Inspector.get_buf_from_key(string[key], Packet, RawBuffer) →bool
•Inspector.get_buf_from_id(uint[id], Packet, RawBuffer) →bool
•Inspector.get_buf_from_type(uint[type], Packet, RawBuffer) →bool
•Inspector.get_splitter(bool[to_server]) →StreamSplitter
Differences: * In Inspector.configure(), the SnortConfig*parameter is passed implicitly. * the overloaded get_
buf() member function has been split into three separate methods.
IpsOption
•IpsOption.hash() →int
•IpsOption.is_relative() →bool
•IpsOption.fp_research() →bool
•IpsOption.get_cursor_type() →int
•IpsOption.eval(Cursor, Packet) →int
•IpsOption.action(Packet)
IpsAction
•IpsAction.exec(Packet)
Logger
•Logger.open()
•Logger.close()
•Logger.reset()
•Logger.alert(Packet, string[message], Event)
•Logger.log(Packet, string[message], Event)
SearchEngine
Currently, SearchEngine does not expose any methods.
SoRule
Currently, SoRule does not expose any methods.
Snort 3 User Manual 183 / 284
Interface Objects
Many of the plugins take C++ classes and structs as arguments. These objects are exposed to the Lua API as Lua userdata.
Exposed objects are instantiated by calling the new method from each object’s method table.
For example, the DecodeData object can be instantiated and exposed to Lua like this:
local decode_data = DecodeData.new(...)
Each object also exposes useful methods for getting and setting member variables, and calling the C++ methods contained in the
the object. These methods can be accessed using the :accessor syntax:
decode_data:set({ sp = 80, dp = 3500 })
Since this is just syntactic sugar for passing the object as the first parameter of the function DecodeData.set, an equivalent
form is:
decode_data.set(decode_data, { sp = 80, dp = 3500 })
or even:
DecodeData.set(decode_data, { sp = 80, dp = 3500 })
Buffer
•Buffer.new(string[data]) →Buffer
•Buffer.new(uint[length]) →Buffer
•Buffer.new(RawBuffer) →Buffer
•Buffer:allocate(uint[length]) →bool
•Buffer:clear()
CodecData
•CodecData.new() →CodecData
•CodecData.new(uint[next_prot_id]) →CodecData
•CodecData.new(fields) →CodecData
•CodecData:get() →fields
•CodecData:set(fields)
fields is a table with the following contents:
•next_prot_id
•lyr_len
•invalid_bytes
•proto_bits
•codec_flags
•ip_layer_cnt
•ip6_extension_count
Snort 3 User Manual 184 / 284
•curr_ip6_extension
•ip6_csum_proto
Cursor
•Cursor.new() →Cursor
•Cursor.new(Packet) →Cursor
•Cursor.new(string[data]) →Cursor
•Cursor.new(RawBuffer) →Cursor
•Cursor:reset()
•Cursor:reset(Packet)
•Cursor:reset(string[data])
•Cursor:reset(RawBuffer)
DAQHeader
•DAQHeader.new() →DAQHeader
•DAQHeader.new(fields) →DAQHeader
•DAQHeader:get() →fields
•DAQHeader:set(fields)
fields is a table with the following contents:
•caplen
•pktlen
•ingress_index
•egress_index
•ingress_group
•egress_group
•flags
•opaque
DecodeData
•DecodeData.new() →DecodeData
•DecodeData.new(fields) →DecodeData
•DecodeData:reset()
•DecodeData:get() →fields
•DecodeData:set(fields)
•DecodeData:set_ipv4_hdr(RawBuffer, uint[offset])
Snort 3 User Manual 185 / 284
fields is a table with the following contents:
•sp
•dp
•decode_flags
•type
EncState
•EncState.new() →EncState
•EncState.new(uint[flags_lo]) →EncState
•EncState.new(uint[flags_lo], uint[flags_hi]) →EncState
•EncState.new(uint[flags_lo], uint[flags_hi], uint[next_proto]) →EncState
•EncState.new(uint[flags_lo], uint[flags_hi], uint[next_proto], uint[ttl]) →EncState
•EncState.new(uint[flags_lo], uint[flags_hi], uint[next_proto], uint[ttl], uint[dsize
]) →EncState
Event
•Event.new() →Event
•Event.new(fields) →Event
•Event:get() →fields
•Event:set(fields)
fields is a table with the following contents:
•event_id
•event_reference
•sig_info
–generator
–id
–rev
–class_id
–priority
–text_rule
–num_services
Flow
•Flow.new() →Flow
•Flow:reset()
Packet
Snort 3 User Manual 186 / 284
•Packet.new() →Packet
•Packet.new(string[data]) →Packet
•Packet.new(uint[size]) →Packet
•Packet.new(fields) →Packet
•Packet.new(RawBuffer) →Packet
•Packet.new(DAQHeader) →Packet
•Packet:set_decode_data(DecodeData)
•Packet:set_data(uint[offset], uint[length])
•Packet:set_flow(Flow)
•Packet:get() →fields
•Packet:set()
•Packet:set(string[data])
•Packet:set(uint[size])
•Packet:set(fields)
•Packet:set(RawBuffer)
•Packet:set(DAQHeader)
fields is a table with the following contents:
•packet_flags
•xtradata_mask
•proto_bits
•application_protocol_ordinal
•alt_dsize
•num_layers
•iplist_id
•user_policy_id
•ps_proto
Note: Packet.new() and Packet:set() accept multiple arguments of the types described above in any order
RawBuffer
•RawBuffer.new() →RawBuffer
•RawBuffer.new(uint[size]) →RawBuffer
•RawBuffer.new(string[data]) →RawBuffer
•RawBuffer:size() →int
•RawBuffer:resize(uint[size])
•RawBuffer:write(string[data])
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•RawBuffer:write(string[data], uint[size])
•RawBuffer:read() →string
•RawBuffer:read(uint[end]) →string
•RawBuffer:read(uint[start], uint[end]) →string
Note: calling RawBuffer.new() with no arguments returns a RawBuffer of size 0
StreamSplitter
•StreamSplitter:scan(Flow, RawBuffer) →int, int
•StreamSplitter:scan(Flow, RawBuffer, uint[len]) →int, int
•StreamSplitter:scan(Flow, RawBuffer, uint[len], uint[flags]) →int, int
•StreamSplitter:reassemble(Flow, uint[total], uint[offset], RawBuffer) →int, RawBuffer
•StreamSplitter:reassemble(Flow, uint[total], uint[offset], RawBuffer, uint[len]) →i
nt, RawBuffer
•StreamSplitter:reassemble(Flow, uint[total], uint[offset], RawBuffer, uint[len], uin
t[flags]) →int, RawBuffer
•StreamSplitter:finish(Flow) →bool
Note: StreamSplitter does not have a new() method, it must be created by an inspector via Inspector.get_splitter()
19 Coding Style
All new code should try to follow these style guidelines. These are not yet firm so feedback is welcome to get something we can
live with.
19.1 General
• Generally try to follow http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml, but there are some differences doc-
umented here.
• Each source directory should have a dev_notes.txt file summarizing the key points and design decisions for the code in that
directory. These are built into the developers guide.
• Makefile.am and CMakeLists.txt should have the same files listed in alpha order. This makes it easier to maintain both build
systems.
• All new code must come with unit tests providing 95% coverage or better.
• Generally, Catch is preferred for tests in the source file and CppUTest is preferred for test executables in a test subdirectory.
19.2 C++ Specific
• Do not use exceptions. Exception-safe code is non-trivial and we have ported legacy code that makes use of exceptions unwise.
There are a few exceptions to this rule for the memory manager, shell, etc. Other code should handle errors as errors.
• Do not use dynamic_cast or RTTI. Although compilers are getting better all the time, there is a time and space cost to this that
is easily avoided.
Snort 3 User Manual 188 / 284
• Use smart pointers judiciously as they aren’t free. If you would have to roll your own, then use a smart pointer. If you just
need a dtor to delete something, write the dtor.
• Prefer and over && and or over || for new source files.
• Use nullptr instead of NULL.
• Use new, delete, and their [] counterparts instead of malloc and free except where realloc must be used. But try not to use
realloc. New and delete can’t return nullptr so no need to check. And Snort’s memory manager will ensure that we live within
our memory budget.
• Use references in lieu of pointers wherever possible.
• Use the order public, protected, private top to bottom in a class declaration.
• Keep inline functions in a class declaration very brief, preferably just one line. If you need a more complex inline function,
move the definition below the class declaration.
• The goal is to have highly readable class declarations. The user shouldn’t have to sift through implementation details to see
what is available to the client.
• Any using statements in source files should be added only after all includes have been declared.
19.3 Naming
• Use camel case for namespaces, classes, and types like WhizBangPdfChecker.
• Use lower case identifiers with underscore separators, e.g. some_function() and my_var.
• Do not start or end variable names with an underscore. This has a good chance of conflicting with macro and/or system
definitions.
• Use lower case filenames with underscores.
19.4 Comments
• Write comments sparingly with a mind towards future proofing. Often the comments can be obviated with better code. Clear
code is better than a comment.
• Heed Tim Ottinger’s Rules on Comments (https://disqus.com/by/tim_ottinger/):
1. Comments should only say what the code is incapable of saying.
2. Comments that repeat (or pre-state) what the code is doing must be removed.
3. If the code CAN say what the comment is saying, it must be changed at least until rule #2 is in force.
• Function comment blocks are generally just noise that quickly becomes obsolete. If you absolutely must comment on pa-
rameters, put each on a separate line along with the comment. That way changing the signature may prompt a change to the
comments too.
• Use FIXIT (not FIXTHIS or TODO or whatever) to mark things left for a day or even just a minute. That way we can find
them easily and won’t lose track of them.
• Presently using FIXIT-X where X = A | W | P | H | M | L, indicating analysis, warning, perf, high, med, or low priority. Place
A and W comments on the exact warning line so we can match up comments and build output. Supporting comments can be
added above.
• Put the copyright(s) and license in a comment block at the top of each source file (.h and .cc). Don’t bother with trivial scripts
and make foo. Some interesting Lua code should get a comment block too. Copy and paste exactly from src/main.h (don’t
reformat).
Snort 3 User Manual 189 / 284
• Put author, description, etc. in separate comment(s) following the license. Do not put such comments in the middle of the
license foo. Be sure to put the author line ahead of the header guard to exclude them from the developers guide. Use the
following format, and include a mention to the original author if this is derived work:
// ips_dnp3_obj.cc author Maya Dagon <mdagon@cisco.com>
// based on work by Ryan Jordan
• Each header should have a comment immediately after the header guard to give an overview of the file so the reader knows
what’s going on.
• Use the following comment on switch cases that intentionally fall through to the next case to suppress compiler warning on
known valid cases:
// fallthrough
19.5 Logging
• Messages intended for the user should not look like debug messages. Eg, the function name should not be included. It is
generally unhelpful to include pointers.
• Most debug messages should just be deleted.
• Don’t bang your error messages (no !). The user feels bad enough about the problem already w/o you shouting at him.
19.6 Types
• Use logical types to make the code clearer and to help the compiler catch problems. typedef uint16_t Port; bool foo(Port) is
way better than int foo(int port).
• Use forward declarations (e.g. struct SnortConfig;) instead of void*.
• Try not to use extern data unless absolutely necessary and then put the extern in an appropriate header. Exceptions for things
used in exactly one place like BaseApi pointers.
• Use const liberally. In most cases, const char* s = "foo" should be const char* const s = "foo". The former goes in the initialized
data section and the latter in read only data section.
• But use const char s[] = "foo" instead of const char* s = "foo" when possible. The latter form allocates a pointer variable and
the data while the former allocates only the data.
• Use static wherever possible to minimize public symbols and eliminate unneeded relocations.
• Declare functions virtual only in the parent class introducing the function (not in a derived class that is overriding the function).
This makes it clear which class introduces the function.
• Declare functions as override if they are intended to override a function. This makes it possible to find derived implementations
that didn’t get updated and therefore won’t get called due a change in the parent signature.
• Use bool functions instead of int unless there is truly a need for multiple error returns. The C-style use of zero for success
and -1 for error is less readable and often leads to messy code that either ignores the various errors anyway or needlessly and
ineffectively tries to do something about them. Generally that code is not updated if new errors are added.
Snort 3 User Manual 190 / 284
19.7 Macros (aka defines)
• In many cases, even in C++, use #define name "value" instead of a const char* const name = "value" because it will eliminate
a symbol from the binary.
• Use inline functions instead of macros where possible (pretty much all cases except where stringification is necessary). Func-
tions offer better typing, avoid re-expansions, and a debugger can break there.
• All macros except simple const values should be wrapped in () and all args should be wrapped in () too to avoid surprises upon
expansion. Example:
#define SEQ_LT(a,b) ((int)((a) - (b)) < 0)
• Multiline macros should be blocked (i.e. inside { }) to avoid if-else type surprises.
19.8 Formatting
• Try to keep all source files under 2500 lines. 3000 is the max allowed. If you need more lines, chances are that the code needs
to be refactored.
• Indent 4 space chars . . . no tabs!
• If you need to indent many times, something could be rewritten or restructured to make it clearer. Fewer indents is generally
easier to write, easier to read, and overall better code.
• Braces go on the line immediately following a new scope (function signature, if, else, loop, switch, etc.
• Use consistent spacing and line breaks. Always indent 4 spaces from the breaking line. Keep lines less than 100 chars; it
greatly helps readability.
No:
calling_a_func_with_a_long_name(arg1,
arg2,
arg3);
Yes:
calling_a_func_with_a_long_name(
arg1, arg2, arg3);
• Put function signature on one line, except when breaking for the arg list:
No:
inline
bool foo()
{ // ...
Yes:
inline bool foo()
{ // ...
• Put conditional code on the line following the if so it is easy to break on the conditional block:
No:
if ( test ) foo();
Yes:
if ( test )
foo();
Snort 3 User Manual 191 / 284
19.9 Headers
• Don’t hesitate to create a new header if it is needed. Don’t lump unrelated stuff into an header because it is convenient.
• Write header guards like this (leading underscores are reserved for system stuff). In my_header.h:
#ifndef MY_HEADER_H
#define MY_HEADER_H
// ...
#endif
• Includes from a different directory should specify parent directory. This makes it clear exactly what is included and avoids the
primordial soup that results from using -I this -I that -I the_other_thing . . . .
// given:
src/foo/foo.cc
src/bar/bar.cc
src/bar/baz.cc
// in baz.cc
#include "bar.h"
// in foo.cc
#include "bar/bar.h"
• Includes within installed headers should specify parent directory.
• Just because it is a #define doesn’t mean it goes in a header. Everything should be scoped as tightly as possible. Shared
implementation declarations should go in a separate header from the interface. And so on.
• All .cc files should include config.h with the standard block shown below immediately following the initial comment blocks and
before anything else. This presents a consistent view of all included header files as well as access to any other configure-time
definitions. No .h files should include config.h unless they are guaranteed to be local header files (never installed).
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
• A .cc should include its own .h before any others aside from the aforementioned config.h (including system headers). This
ensures that the header stands on its own and can be used by clients without include prerequisites and the developer will be the
first to find a dependency issue.
• Split headers included from the local directory into a final block of headers. For a .cc file, the final order of sets of header
includes should look like this:
1. config.h
2. its own .h file
3. system headers (.h/.hpp/.hxx)
4. C++ standard library headers (no file extension)
5. Snort headers external to the local directory (path-prefixed)
6. Snort headers in the local directory
• Include required headers, all required headers, and nothing but required headers. Don’t just clone a bunch of headers because
it is convenient.
• Keep includes in alphabetical order. This makes it easier to maintain, avoid duplicates, etc.
• Do not put using statements in headers unless they are tightly scoped.
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19.10 Warnings
• With g++, use at least these compiler flags:
-Wall -Wextra -pedantic -Wformat -Wformat-security
-Wunused-but-set-variable -Wno-deprecated-declarations
-fsanitize=address -fno-omit-frame-pointer
• With clang, use at least these compiler flags:
-Wall -Wextra -pedantic -Wformat -Wformat-security
-Wno-deprecated-declarations
-fsanitize=address -fno-omit-frame-pointer
• Two macros (PADDING_GUARD_BEGIN and PADDING_GUARD_END) are provided by utils/cpp_macros.h. These should
be used to surround any structure used as a hash key with a raw comparator or that would otherwise suffer from unintentional
padding. A compiler warning will be generated if any structure definition is automatically padded between the macro invoca-
tions.
• Then Fix All Warnings and Aborts. None Allowed.
19.11 Uncrustify
Currently using uncrustify from at https://github.com/bengardner/uncrustify to reformat legacy code and anything that happens
to need a makeover at some point.
The working config is crusty.cfg in the top level directory. It does well but will munge some things. Specially formatted
INDENT-OFF comments were added in 2 places to avoid a real mess.
You can use uncrustify something like this:
uncrustify -c crusty.cfg --replace file.cc
20 Reference
20.1 Build Options
The options listed below must be explicitly enabled so they are built into the Snort binary. For a full list of build options, run
./configure --help.
•--enable-shell: enable building local and remote command line shell support.
•--enable-tsc-clock: use the TSC register on x86 systems for improved performance of latency and profiler features.
These options are built only if the required libraries and headers are present. There is no need to explicitly enable.
•flatbuffers: for an alternative perf_monitor logging format.
•hyperscan >= 4.4.0: for the regex and sd_pattern rule options and the hyperscan search engine.
•iconv: for converting UTF16-LE filenames to UTF8 (usually included in glibc)
•lzma: for decompression of SWF and PDF files.
•safec: for additional runtime error checking of some memory copy operations.
If you need to use headers and/or libraries in non-standard locations, you can use these options:
Snort 3 User Manual 193 / 284
•--with-pkg-includes: specify the directory containing the package headers.
•--with-pkg-libraries: specify the directory containing the package libraries.
These can be used for pcap, luajit, pcre, dnet, daq, lzma, openssl, flatbuffers, iconv, and hyperscan packages. For more informa-
tion on these libraries see the Getting Started section of the manual.
20.2 Environment Variables
•HOSTTYPE: optional string that is output with the version at end of line.
•LUA_PATH: you must export as follows so LuaJIT can find required files.
LUA_PATH=$install_dir/include/snort/lua/\?.lua\;\;
•SNORT_IGNORE: the list of symbols Snort should ignore when parsing the Lua conf. Unknown symbols not in SNORT_IGNORE
will cause warnings with --warn-unknown or fatals with --warn-unknown --pedantic.
•SNORT_LUA_PATH: an optional path where Snort can find supplemental conf files such as classification.lua.
•SNORT_PROMPT: the character sequence that is printed at startup, shutdown, and in the shell. The default is the mini-pig:
o")~ .
•SNORT_PLUGIN_PATH: an optional path where Snort can find supplemental shared libraries. This is only used when Snort
is building manuals. Modules in supplemental shared libraries will be added to the manuals.
20.3 Command Line Options
•--alert-before-pass process alert, drop, sdrop, or reject before pass; default is pass before alert, drop,. . .
•-A <mode> set alert mode: none, cmg, or alert_*
•-B <mask> obfuscated IP addresses in alerts and packet dumps using CIDR mask
•--bpf <filter options> are standard BPF options, as seen in TCPDump
•--c2x output hex for given char (see also --x2c)
•--catch-test comma separated list of cat unit test tags or all
•-c <conf> use this configuration
•--control-socket <file> to create unix socket
•-C print out payloads with character data only (no hex)
•--create-pidfile create PID file, even when not in Daemon mode
•--daq-dir <dir> tell snort where to find desired DAQ
•--daq-list list packet acquisition modules available in optional dir, default is static modules only
•--daq <type> select packet acquisition module (default is pcap)
•--daq-var <name=value> specify extra DAQ configuration variable
•-d dump the Application Layer
•--dirty-pig don’t flush packets on shutdown
•-D run Snort in background (daemon) mode
•--dump-builtin-rules [<module prefix>] output stub rules for selected modules (optional)
Snort 3 User Manual 194 / 284
•--dump-defaults [<module prefix>] output module defaults in Lua format (optional)
•--dump-dynamic-rules output stub rules for all loaded rules libraries
•--dump-version output the version, the whole version, and only the version
•-e display the second layer header info
•--enable-inline-test enable Inline-Test Mode Operation
•-f turn off fflush() calls after binary log writes
•-G <0xid> (same as --logid) (0:65535)
•--gen-msg-map dump builtin rules in gen-msg.map format for use by other tools
•-g <gname> run snort gid as <gname> group (or gid) after initialization
•--help-commands [<module prefix>] output matching commands (optional)
•--help-config [<module prefix>] output matching config options (optional)
•--help-counts [<module prefix>] output matching peg counts (optional)
•--help list command line options
•--help-module <module> output description of given module
•--help-modules list all available modules with brief help
•--help-options [<option prefix>] output matching command line option quick help (same as -?) (optional)
•--help-plugins list all available plugins with brief help
•--help-signals dump available control signals
•-H make hash tables deterministic
•--id-offset offset to add to instance IDs when logging to files (0:65535)
•--id-subdir create/use instance subdirectories in logdir instead of instance filename prefix
•--id-zero use id prefix / subdirectory even with one packet thread
•-i <iface>. . . list of interfaces
•-j <port> to listen for Telnet connections
•-k <mode> checksum mode; default is all (all|noip|notcp|noudp|noicmp|none)
•--list-buffers output available inspection buffers
•--list-builtin [<module prefix>] output matching builtin rules (optional)
•--list-gids [<module prefix>] output matching generators (optional)
•--list-modules [<module type>] list all known modules of given type (optional)
•--list-plugins list all known plugins
•-l <logdir> log to this directory instead of current directory
•-L <mode> logging mode (none, dump, pcap, or log_*)
•--logid <0xid> log Identifier to uniquely id events for multiple snorts (same as -G) (0:65535)
•--lua <chunk> extend/override conf with chunk; may be repeated
•--markup output help in asciidoc compatible format
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•--max-packet-threads <count> configure maximum number of packet threads (same as -z) (0:)
•--mem-check like -T but also compile search engines
•-M log messages to syslog (not alerts)
•-m <umask> set umask = <umask> (0:)
•-n <count> stop after count packets (0:)
•--nolock-pidfile do not try to lock Snort PID file
•--nostamps don’t include timestamps in log file names
•-O obfuscate the logged IP addresses
•-? <option prefix> output matching command line option quick help (same as --help-options) (optional)
•--parsing-follows-files parse relative paths from the perspective of the current configuration file
•--pause wait for resume/quit command before processing packets/terminating
•--pcap-dir <dir> a directory to recurse to look for pcaps - read mode is implied
•--pcap-file <file> file that contains a list of pcaps to read - read mode is implied
•--pcap-filter <filter> filter to apply when getting pcaps from file or directory
•--pcap-list <list> a space separated list of pcaps to read - read mode is implied
•--pcap-loop <count> read all pcaps <count> times; 0 will read until Snort is terminated (-1:)
•--pcap-no-filter reset to use no filter when getting pcaps from file or directory
•--pcap-reload if reading multiple pcaps, reload snort config between pcaps
•--pcap-show print a line saying what pcap is currently being read
•--pedantic warnings are fatal
•--piglet enable piglet test harness mode
•--plugin-path <path> where to find plugins
•--process-all-events process all action groups
•-Q enable inline mode operation
•-q quiet mode - Don’t show banner and status report
•-r <pcap>. . . (same as --pcap-list)
•-R <rules> include this rules file in the default policy
•--rule <rules> to be added to configuration; may be repeated
•--rule-to-hex output so rule header to stdout for text rule on stdin
•--rule-to-text output plain so rule header to stdout for text rule on stdin
•--run-prefix <pfx> prepend this to each output file
•--script-path <path> to a luajit script or directory containing luajit scripts
•--shell enable the interactive command line
•--show-plugins list module and plugin versions
•--skip <n> skip 1st n packets (0:)
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•--snaplen <snap> set snaplen of packet (same as -s) (68:65535)
•-s <snap> (same as --snaplen); default is 1514 (68:65535)
•--stdin-rules read rules from stdin until EOF or a line starting with END is read
•-S <x=v> set config variable x equal to value v
•-t <dir> chroots process to <dir> after initialization
•--treat-drop-as-alert converts drop, sdrop, and reject rules into alert rules during startup
•--treat-drop-as-ignore use drop, sdrop, and reject rules to ignore session traffic when not inline
•-T test and report on the current Snort configuration
•-u <uname> run snort as <uname> or <uid> after initialization
•-U use UTC for timestamps
•-v be verbose
•--version show version number (same as -V)
•-V (same as --version)
•--warn-all enable all warnings
•--warn-conf warn about configuration issues
•--warn-daq warn about DAQ issues, usually related to mode
•--warn-flowbits warn about flowbits that are checked but not set and vice-versa
•--warn-hosts warn about host table issues
•--warn-plugins warn about issues that prevent plugins from loading
•--warn-rules warn about duplicate rules and rule parsing issues
•--warn-scripts warn about issues discovered while processing Lua scripts
•--warn-symbols warn about unknown symbols in your Lua config
•--warn-vars warn about variable definition and usage issues
•-W lists available interfaces
•--x2c output ASCII char for given hex (see also --c2x)
•--x2s output ASCII string for given byte code (see also --x2c)
•-X dump the raw packet data starting at the link layer
•-x same as --pedantic
•-y include year in timestamp in the alert and log files
•-z <count> maximum number of packet threads (same as --max-packet-threads); 0 gets the number of CPU cores reported by
the system; default is 1 (0:)
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20.4 Configuration
• interval ack.~range: check if TCP ack value is value | min<>max | <max | >min { 0: }
• int active.attempts = 0: number of TCP packets sent per response (with varying sequence numbers) { 0:20 }
• string active.device: use ip for network layer responses or eth0 etc for link layer
• string active.dst_mac: use format 01:23:45:67:89:ab
• int active.max_responses = 0: maximum number of responses { 0: }
• int active.min_interval = 255: minimum number of seconds between responses { 1: }
• multi alert_csv.fields = timestamp pkt_num proto pkt_gen pkt_len dir src_ap dst_ap rule action: selected fields will be output
in given order left to right { action | class | b64_data | dir | dst_addr | dst_ap | dst_port | eth_dst | eth_len | eth_src | eth_type |
gid | icmp_code | icmp_id | icmp_seq | icmp_type | iface | ip_id | ip_len | msg | mpls | pkt_gen | pkt_len | pkt_num | priority |
proto | rev | rule | seconds | service | sid | src_addr | src_ap | src_port | target | tcp_ack | tcp_flags | tcp_len | tcp_seq | tcp_win |
timestamp | tos | ttl | udp_len | vlan }
• bool alert_csv.file = false: output to alert_csv.txt instead of stdout
• int alert_csv.limit = 0: set maximum size in MB before rollover (0 is unlimited) { 0: }
• string alert_csv.separator = , : separate fields with this character sequence
• bool alert_ex.upper = false: true/false →convert to upper/lower case
• bool alert_fast.file = false: output to alert_fast.txt instead of stdout
• int alert_fast.limit = 0: set maximum size in MB before rollover (0 is unlimited) { 0: }
• bool alert_fast.packet = false: output packet dump with alert
• bool alert_full.file = false: output to alert_full.txt instead of stdout
• int alert_full.limit = 0: set maximum size in MB before rollover (0 is unlimited) { 0: }
• multi alert_json.fields = timestamp pkt_num proto pkt_gen pkt_len dir src_ap dst_ap rule action: selected fields will be output
in given order left to right { action | class | b64_data | dir | dst_addr | dst_ap | dst_port | eth_dst | eth_len | eth_src | eth_type |
gid | icmp_code | icmp_id | icmp_seq | icmp_type | iface | ip_id | ip_len | msg | mpls | pkt_gen | pkt_len | pkt_num | priority |
proto | rev | rule | seconds | service | sid | src_addr | src_ap | src_port | target | tcp_ack | tcp_flags | tcp_len | tcp_seq | tcp_win |
timestamp | tos | ttl | udp_len | vlan }
• bool alert_json.file = false: output to alert_json.txt instead of stdout
• int alert_json.limit = 0: set maximum size in MB before rollover (0 is unlimited) { 0: }
• string alert_json.separator = , : separate fields with this character sequence
• bool alerts.alert_with_interface_name = false: include interface in alert info (fast, full, or syslog only)
• bool alerts.default_rule_state = true: enable or disable ips rules
• int alerts.detection_filter_memcap = 1048576: set available bytes of memory for detection_filters { 0: }
• int alerts.event_filter_memcap = 1048576: set available bytes of memory for event_filters { 0: }
• string alert_sfsocket.file: name of unix socket file
• int alert_sfsocket.rules[].gid = 1: rule generator ID { 1: }
• int alert_sfsocket.rules[].sid = 1: rule signature ID { 1: }
• bool alerts.log_references = false: include rule references in alert info (full only)
• string alerts.order = pass drop alert log: change the order of rule action application
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• int alerts.rate_filter_memcap = 1048576: set available bytes of memory for rate_filters { 0: }
• string alerts.reference_net: set the CIDR for homenet (for use with -l or -B, does NOT change $HOME_NET in IDS mode)
• bool alerts.stateful = false: don’t alert w/o established session (note: rule action still taken)
• string alerts.tunnel_verdicts: let DAQ handle non-allow verdicts for gtp|teredo|6in4|4in6|4in4|6in6|gre|mpls traffic
• enum alert_syslog.facility = auth: part of priority applied to each message { auth | authpriv | daemon | user | local0 | local1 |
local2 | local3 | local4 | local5 | local6 | local7 }
• enum alert_syslog.level = info: part of priority applied to each message { emerg | alert | crit | err | warning | notice | info | debug
}
• multi alert_syslog.options: used to open the syslog connection { cons | ndelay | perror | pid }
• string appid.app_detector_dir: directory to load appid detectors from
• int appid.app_stats_period = 300: time period for collecting and logging appid statistics { 0: }
• int appid.app_stats_rollover_size = 20971520: max file size for appid stats before rolling over the log file { 0: }
• int appid.app_stats_rollover_time = 86400: max time period for collection appid stats before rolling over the log file { 0: }
• bool appid.debug = false: enable appid debug logging
• bool appid.dump_ports = false: enable dump of appid port information
• int appid.instance_id = 0: instance id - ignored { 0: }
• bool appid.log_all_sessions = false: enable logging of all appid sessions
• bool appid.log_stats = false: enable logging of appid statistics
• int appid.memcap = 0: disregard - not implemented { 0: }
• string appids.~: comma separated list of application names
• addr appid.session_log_filter.dst_ip = 0.0.0.0/32: destination IP address in CIDR format
• port appid.session_log_filter.dst_port: destination port { 1: }
• bool appid.session_log_filter.log_all_sessions = false: enable logging for all appid sessions
• string appid.session_log_filter.protocol: IP protocol
• addr appid.session_log_filter.src_ip = 0.0.0.0/32: source IP address in CIDR format
• port appid.session_log_filter.src_port: source port { 1: }
• ip4 arp_spoof.hosts[].ip: host ip address
• mac arp_spoof.hosts[].mac: host mac address
• int asn1.absolute_offset: absolute offset from the beginning of the packet { 0: }
• implied asn1.bitstring_overflow: detects invalid bitstring encodings that are known to be remotely exploitable
• implied asn1.double_overflow: detects a double ASCII encoding that is larger than a standard buffer
• int asn1.oversize_length: compares ASN.1 type lengths with the supplied argument { 0: }
• implied asn1.print: dump decode data to console; always true
• int asn1.relative_offset: relative offset from the cursor
• int attribute_table.max_hosts = 1024: maximum number of hosts in attribute table { 32:207551 }
• int attribute_table.max_metadata_services = 8: maximum number of services in rule metadata { 1:256 }
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• int attribute_table.max_services_per_host = 8: maximum number of services per host entry in attribute table { 1:65535 }
• int base64_decode.bytes: number of base64 encoded bytes to decode { 1: }
• int base64_decode.offset = 0: bytes past start of buffer to start decoding { 0: }
• implied base64_decode.relative: apply offset to cursor instead of start of buffer
• enum binder[].use.action = inspect: what to do with matching traffic { reset | block | allow | inspect }
• string binder[].use.file: use configuration in given file
• string binder[].use.inspection_policy: use inspection policy from given file
• string binder[].use.ips_policy: use ips policy from given file
• string binder[].use.name: symbol name (defaults to type)
• string binder[].use.network_policy: use network policy from given file
• string binder[].use.service: override automatic service identification
• string binder[].use.type: select module for binding
• addr_list binder[].when.dst_nets: list of destination networks
• bit_list binder[].when.dst_ports: list of destination ports { 65535 }
• int binder[].when.dst_zone: destination zone { 0:2147483647 }
• bit_list binder[].when.ifaces: list of interface indices { 255 }
• int binder[].when.ips_policy_id = 0: unique ID for selection of this config by external logic { 0: }
• addr_list binder[].when.nets: list of networks
• bit_list binder[].when.ports: list of ports { 65535 }
• enum binder[].when.proto: protocol { any | ip | icmp | tcp | udp | user | file }
• enum binder[].when.role = any: use the given configuration on one or any end of a session { client | server | any }
• string binder[].when.service: override default configuration
• addr_list binder[].when.src_nets: list of source networks
• bit_list binder[].when.src_ports: list of source ports { 65535 }
• int binder[].when.src_zone: source zone { 0:2147483647 }
• bit_list binder[].when.vlans: list of VLAN IDs { 4095 }
• interval bufferlen.~range: check that length of current buffer is in given range { 0:65535 }
• int byte_extract.align = 0: round the number of converted bytes up to the next 2- or 4-byte boundary { 0:4 }
• implied byte_extract.big: big endian
• int byte_extract.bitmask: applies as an AND to the extracted value before storage in name { 0x1:0xFFFFFFFF }
• int byte_extract.~count: number of bytes to pick up from the buffer { 1:10 }
• implied byte_extract.dce: dcerpc2 determines endianness
• implied byte_extract.dec: convert from decimal string
• implied byte_extract.hex: convert from hex string
• implied byte_extract.little: little endian
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• int byte_extract.multiplier = 1: scale extracted value by given amount { 1:65535 }
• string byte_extract.~name: name of the variable that will be used in other rule options
• implied byte_extract.oct: convert from octal string
• int byte_extract.~offset: number of bytes into the buffer to start processing { -65535:65535 }
• implied byte_extract.relative: offset from cursor instead of start of buffer
• implied byte_extract.string: convert from string
• int byte_jump.align = 0: round the number of converted bytes up to the next 2- or 4-byte boundary { 0:4 }
• implied byte_jump.big: big endian
• int byte_jump.bitmask: applies as an AND prior to evaluation { 0x1:0xFFFFFFFF }
• int byte_jump.~count: number of bytes to pick up from the buffer { 0:10 }
• implied byte_jump.dce: dcerpc2 determines endianness
• implied byte_jump.dec: convert from decimal string
• implied byte_jump.from_beginning: jump from start of buffer instead of cursor
• implied byte_jump.from_end: jump backward from end of buffer
• implied byte_jump.hex: convert from hex string
• implied byte_jump.little: little endian
• int byte_jump.multiplier = 1: scale extracted value by given amount { 1:65535 }
• implied byte_jump.oct: convert from octal string
• string byte_jump.~offset: variable name or number of bytes into the buffer to start processing
• int byte_jump.post_offset = 0: also skip forward or backwards (positive of negative value) this number of bytes { -65535:65535
}
• implied byte_jump.relative: offset from cursor instead of start of buffer
• implied byte_jump.string: convert from string
• int byte_math.bitmask: applies as bitwise AND to the extracted value before storage in name { 0x1:0xFFFFFFFF }
• int byte_math.bytes: number of bytes to pick up from the buffer { 1:10 }
• implied byte_math.dce: dcerpc2 determines endianness
• enum byte_math.endian: specify big/little endian { big|little }
• string byte_math.offset: number of bytes into the buffer to start processing
• enum byte_math.oper: mathematical operation to perform { +|-|*|/|<<|>> }
• implied byte_math.relative: offset from cursor instead of start of buffer
• string byte_math.result: name of the variable to store the result
• string byte_math.rvalue: value to use mathematical operation against
• enum byte_math.string: convert extracted string to dec/hex/oct { hex|dec|oct }
• implied byte_test.big: big endian
• int byte_test.bitmask: applies as an AND prior to evaluation { 0x1:0xFFFFFFFF }
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• string byte_test.~compare: variable name or value to test the converted result against
• int byte_test.~count: number of bytes to pick up from the buffer { 1:10 }
• implied byte_test.dce: dcerpc2 determines endianness
• implied byte_test.dec: convert from decimal string
• implied byte_test.hex: convert from hex string
• implied byte_test.little: little endian
• implied byte_test.oct: convert from octal string
• string byte_test.~offset: variable name or number of bytes into the payload to start processing
• string byte_test.~operator: variable name or number of bytes into the buffer to start processing
• implied byte_test.relative: offset from cursor instead of start of buffer
• implied byte_test.string: convert from string
• string classifications[].name: name used with classtype rule option
• int classifications[].priority = 1: default priority for class { 0: }
• string classifications[].text: description of class
• string classtype.~: classification for this rule
• string content.~data: data to match
• string content.depth: var or maximum number of bytes to search from beginning of buffer
• string content.distance: var or number of bytes from cursor to start search
• int content.fast_pattern_length: maximum number of characters from this content the fast pattern matcher should use { 1: }
• int content.fast_pattern_offset = 0: number of leading characters of this content the fast pattern matcher should exclude { 0:
}
• implied content.fast_pattern: use this content in the fast pattern matcher instead of the content selected by default
• implied content.nocase: case insensitive match
• string content.offset: var or number of bytes from start of buffer to start search
• string content.within: var or maximum number of bytes to search from cursor
• implied cvs.invalid-entry: looks for an invalid Entry string
• string daq.input_spec: input specification
• int daq.instances[].id: instance ID (required) { 0: }
• string daq.instances[].input_spec: input specification
• string daq.instances[].variables[].str: string parameter
• string daq.module: DAQ module to use
• string daq.module_dirs[].str: string parameter
• bool daq.no_promisc = false: whether to put DAQ device into promiscuous mode
• int daq.snaplen: set snap length (same as -s) { 0:65535 }
• string daq.variables[].str: string parameter
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• select data_log.key = http_request_header_event : name of the event to log { http_request_header_event | http_response_header_event
}
• int data_log.limit = 0: set maximum size in MB before rollover (0 is unlimited) { 0: }
• implied dce_iface.any_frag: match on any fragment
• string dce_iface.uuid: match given dcerpc uuid
• interval dce_iface.version: interface version { 0: }
• string dce_opnum.~: match given dcerpc operation number, range or list
• bool dce_smb.disable_defrag = false: Disable DCE/RPC defragmentation
• int dce_smb.max_frag_len = 65535: Maximum fragment size for defragmentation { 1514:65535 }
• enum dce_smb.policy = WinXP: Target based policy to use { Win2000 | WinXP | WinVista | Win2003 | Win2008 | Win7 |
Samba | Samba-3.0.37 | Samba-3.0.22 | Samba-3.0.20 }
• int dce_smb.reassemble_threshold = 0: Minimum bytes received before performing reassembly { 0:65535 }
• int dce_smb.smb_file_depth = 16384: SMB file depth for file data { -1: }
• enum dce_smb.smb_file_inspection = off: SMB file inspection { off | on | only }
• enum dce_smb.smb_fingerprint_policy = none: Target based SMB policy to use { none | client | server | both }
• string dce_smb.smb_invalid_shares: SMB shares to alert on
• bool dce_smb.smb_legacy_mode = false: inspect only SMBv1
• int dce_smb.smb_max_chain = 3: SMB max chain size { 0:255 }
• int dce_smb.smb_max_compound = 3: SMB max compound size { 0:255 }
• multi dce_smb.valid_smb_versions = all: Valid SMB versions { v1 | v2 | all }
• bool dce_tcp.disable_defrag = false: Disable DCE/RPC defragmentation
• int dce_tcp.max_frag_len = 65535: Maximum fragment size for defragmentation { 1514:65535 }
• enum dce_tcp.policy = WinXP: Target based policy to use { Win2000 | WinXP | WinVista | Win2003 | Win2008 | Win7 |
Samba | Samba-3.0.37 | Samba-3.0.22 | Samba-3.0.20 }
• int dce_tcp.reassemble_threshold = 0: Minimum bytes received before performing reassembly { 0:65535 }
• bool dce_udp.disable_defrag = false: Disable DCE/RPC defragmentation
• int dce_udp.max_frag_len = 65535: Maximum fragment size for defragmentation { 1514:65535 }
• int detection.asn1 = 256: maximum decode nodes { 1: }
• int detection_filter.count: hits in interval before allowing the rule to fire { 1: }
• int detection_filter.seconds: length of interval to count hits { 1: }
• enum detection_filter.track: track hits by source or destination IP address { by_src | by_dst }
• int detection.offload_limit = 99999: minimum sizeof PDU to offload fast pattern search (defaults to disabled) { 0: }
• int detection.offload_threads = 0: maximum number of simultaneous offloads (defaults to disabled) { 0: }
• bool detection.pcre_enable = true: disable pcre pattern matching
• int detection.pcre_match_limit = 1500: limit pcre backtracking, -1 = max, 0 = off { -1:1000000 }
• int detection.pcre_match_limit_recursion = 1500: limit pcre stack consumption, -1 = max, 0 = off { -1:10000 }
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• int detection.trace: mask for enabling debug traces in module
• bool dnp3.check_crc = false: validate checksums in DNP3 link layer frames
• string dnp3_func.~: match DNP3 function code or name
• string dnp3_ind.~: match given DNP3 indicator flags
• int dnp3_obj.group = 0: match given DNP3 object header group { 0:255 }
• int dnp3_obj.var = 0: match given DNP3 object header var { 0:255 }
• int dpx.max = 0: maximum payload before alert { 0:65535 }
• port dpx.port: port to check
• interval dsize.~range: check if packet payload size is in the given range { 0:65535 }
• bool esp.decode_esp = false: enable for inspection of esp traffic that has authentication but not encryption
• int event_filter[].count = 0: number of events in interval before tripping; -1 to disable { -1: }
• int event_filter[].gid = 1: rule generator ID { 0: }
• string event_filter[].ip: restrict filter to these addresses according to track
• int event_filter[].seconds = 0: count interval { 0: }
• int event_filter[].sid = 1: rule signature ID { 0: }
• enum event_filter[].track: filter only matching source or destination addresses { by_src | by_dst }
• enum event_filter[].type: 1st count events | every count events | once after count events { limit | threshold | both }
• int event_queue.log = 3: maximum events to log { 1: }
• int event_queue.max_queue = 8: maximum events to queue { 1: }
• enum event_queue.order_events = content_length: criteria for ordering incoming events { priority|content_length }
• bool event_queue.process_all_events = false: process just first action group or all action groups
• string file_connector.connector: connector name
• enum file_connector.direction: usage { receive | transmit | duplex }
• enum file_connector.format: file format { binary | text }
• string file_connector.name: channel name
• int file_id.block_timeout = 86400: stop blocking after this many seconds { 0: }
• bool file_id.block_timeout_lookup = false: block if lookup times out
• int file_id.capture_block_size = 32768: file capture block size in bytes { 8: }
• int file_id.capture_max_size = 1048576: stop file capture beyond this point { 0: }
• int file_id.capture_memcap = 100: memcap for file capture in megabytes { 0: }
• int file_id.capture_min_size = 0: stop file capture if file size less than this { 0: }
• bool file_id.enable_capture = false: enable file capture
• bool file_id.enable_signature = true: enable signature calculation
• bool file_id.enable_type = true: enable type ID
• bool file_id.file_policy[].use.enable_file_capture = false: true/false →enable/disable file capture
Snort 3 User Manual 204 / 284
• bool file_id.file_policy[].use.enable_file_signature = false: true/false →enable/disable file signature
• bool file_id.file_policy[].use.enable_file_type = false: true/false →enable/disable file type identification
• enum file_id.file_policy[].use.verdict = unknown: what to do with matching traffic { unknown | log | stop | block | reset }
• int file_id.file_policy[].when.file_type_id = 0: unique ID for file type in file magic rule { 0: }
• string file_id.file_policy[].when.sha256: SHA 256
• string file_id.file_rules[].category: file type category
• string file_id.file_rules[].group: comma separated list of groups associated with file type
• int file_id.file_rules[].id = 0: file type id { 0: }
• string file_id.file_rules[].magic[].content: file magic content
• int file_id.file_rules[].magic[].offset = 0: file magic offset { 0: }
• string file_id.file_rules[].msg: information about the file type
• int file_id.file_rules[].rev = 0: rule revision { 0: }
• string file_id.file_rules[].type: file type name
• string file_id.file_rules[].version: file type version
• int file_id.lookup_timeout = 2: give up on lookup after this many seconds { 0: }
• int file_id.max_files_cached = 65536: maximal number of files cached in memory { 8: }
• int file_id.show_data_depth = 100: print this many octets { 0: }
• int file_id.signature_depth = 10485760: stop signature at this point { 0: }
• bool file_id.trace_signature = false: enable runtime dump of signature info
• bool file_id.trace_stream = false: enable runtime dump of file data
• bool file_id.trace_type = false: enable runtime dump of type info
• int file_id.type_depth = 1460: stop type ID at this point { 0: }
• int file_id.verdict_delay = 0: number of queries to return final verdict { 0: }
• bool file_log.log_pkt_time = true: log the packet time when event generated
• bool file_log.log_sys_time = false: log the system time when event generated
• string file_type.~: list of file type IDs to match
• string flags.~mask_flags: these flags are don’t cares
• string flags.~test_flags: these flags are tested
• string flowbits.~arg1: bits or group
• string flowbits.~arg2: group if arg1 is bits
• string flowbits.~command: set|reset|isset|etc.
• implied flow.established: match only during data transfer phase
• implied flow.from_client: same as to_server
• implied flow.from_server: same as to_client
• implied flow.no_frag: match on raw packets only
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• implied flow.no_stream: match on raw packets only
• implied flow.not_established: match only outside data transfer phase
• implied flow.only_frag: match on defragmented packets only
• implied flow.only_stream: match on reassembled packets only
• implied flow.stateless: match regardless of stream state
• implied flow.to_client: match on server responses
• implied flow.to_server: match on client requests
• string fragbits.~flags: these flags are tested
• interval fragoffset.~range: check if ip fragment offset is in given range { 0:8192 }
• bool ftp_client.bounce = false: check for bounces
• addr ftp_client.bounce_to[].address = 1.0.0.0/32: allowed IP address in CIDR format
• port ftp_client.bounce_to[].last_port: optional allowed range from port to last_port inclusive { 0: }
• port ftp_client.bounce_to[].port = 20: allowed port { 1: }
• bool ftp_client.ignore_telnet_erase_cmds = false: ignore erase character and erase line commands when normalizing
• int ftp_client.max_resp_len = -1: maximum FTP response accepted by client { -1: }
• bool ftp_client.telnet_cmds = false: detect Telnet escape sequences on FTP control channel
• bool ftp_server.check_encrypted = false: check for end of encryption
• string ftp_server.chk_str_fmt: check the formatting of the given commands
• string ftp_server.cmd_validity[].command: command string
• string ftp_server.cmd_validity[].format: format specification
• int ftp_server.cmd_validity[].length = 0: specify non-default maximum for command { 0: }
• string ftp_server.data_chan_cmds: check the formatting of the given commands
• string ftp_server.data_rest_cmds: check the formatting of the given commands
• string ftp_server.data_xfer_cmds: check the formatting of the given commands
• int ftp_server.def_max_param_len = 100: default maximum length of commands handled by server; 0 is unlimited { 1: }
• string ftp_server.directory_cmds[].dir_cmd: directory command
• int ftp_server.directory_cmds[].rsp_code = 200: expected successful response code for command { 200: }
• string ftp_server.encr_cmds: check the formatting of the given commands
• bool ftp_server.encrypted_traffic = false: check for encrypted Telnet and FTP
• string ftp_server.file_get_cmds: check the formatting of the given commands
• string ftp_server.file_put_cmds: check the formatting of the given commands
• string ftp_server.ftp_cmds: specify additional commands supported by server beyond RFC 959
• bool ftp_server.ignore_data_chan = false: do not inspect FTP data channels
• bool ftp_server.ignore_telnet_erase_cmds = false: ignore erase character and erase line commands when normalizing
• string ftp_server.login_cmds: check the formatting of the given commands
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• bool ftp_server.print_cmds = false: print command configurations on start up
• bool ftp_server.telnet_cmds = false: detect Telnet escape sequences of FTP control channel
• int gid.~: generator id { 1: }
• string gtp_info.~: info element to match
• int gtp_inspect[].infos[].length = 0: information element type code { 0:255 }
• string gtp_inspect[].infos[].name: information element name
• int gtp_inspect[].infos[].type = 0: information element type code { 0:255 }
• string gtp_inspect[].messages[].name: message name
• int gtp_inspect[].messages[].type = 0: message type code { 0:255 }
• int gtp_inspect[].version = 2: GTP version { 0:2 }
• string gtp_type.~: list of types to match
• int gtp_version.~: version to match { 0:2 }
• bool high_availability.daq_channel = false: enable use of daq data plane channel
• bool high_availability.enable = false: enable high availability
• real high_availability.min_age = 1.0: minimum session life before HA updates { 0.0:100.0 }
• real high_availability.min_sync = 1.0: minimum interval between HA updates { 0.0:100.0 }
• bit_list high_availability.ports: side channel message port list { 65535 }
• int host_cache[].size: size of host cache
• enum hosts[].frag_policy: defragmentation policy { first | linux | bsd | bsd_right | last | windows | solaris }
• addr hosts[].ip = 0.0.0.0/32: hosts address / CIDR
• string hosts[].services[].name: service identifier
• port hosts[].services[].port: port number
• enum hosts[].services[].proto = tcp: IP protocol { tcp | udp }
• enum hosts[].tcp_policy: TCP reassembly policy { first | last | linux | old_linux | bsd | macos | solaris | irix | hpux11 | hpux10 |
windows | win_2003 | vista | proxy }
• enum host_tracker[].frag_policy: defragmentation policy { first | linux | bsd | bsd_right | last | windows | solaris }
• addr host_tracker[].IP = 0.0.0.0/32: hosts address / cidr
• string host_tracker[].services[].name: service identifier
• port host_tracker[].services[].port: port number
• enum host_tracker[].services[].proto = tcp: IP protocol { tcp | udp }
• enum host_tracker[].tcp_policy: TCP reassembly policy { first | last | linux | old_linux | bsd | macos | solaris | irix | hpux11 |
hpux10 | windows | win_2003 | vista | proxy }
• implied http_cookie.request: match against the cookie from the request message even when examining the response
• implied http_cookie.with_body: parts of this rule examine HTTP message body
• implied http_cookie.with_trailer: parts of this rule examine HTTP message trailers
• string http_header.field: restrict to given header. Header name is case insensitive.
Snort 3 User Manual 207 / 284
• implied http_header.request: match against the headers from the request message even when examining the response
• implied http_header.with_body: parts of this rule examine HTTP message body
• implied http_header.with_trailer: parts of this rule examine HTTP message trailers
• bool http_inspect.backslash_to_slash = false: replace \ with / when normalizing URIs
• bit_list http_inspect.bad_characters: alert when any of specified bytes are present in URI after percent decoding { 255 }
• bool http_inspect.decompress_pdf = false: decompress pdf files in response bodies
• bool http_inspect.decompress_swf = false: decompress swf files in response bodies
• string http_inspect.ignore_unreserved: do not alert when the specified unreserved characters are percent-encoded in a
URI.Unreserved characters are 0-9, a-z, A-Z, period, underscore, tilde, and minus. { (optional) }
• bool http_inspect.iis_double_decode = false: perform double decoding of percent encodings to normalize characters
• int http_inspect.iis_unicode_code_page = 1252: code page to use from the IIS unicode map file { 0:65535 }
• bool http_inspect.iis_unicode = false: use IIS unicode code point mapping to normalize characters
• string http_inspect.iis_unicode_map_file: file containing code points for IIS unicode. { (optional) }
• int http_inspect.max_javascript_whitespaces = 200: maximum consecutive whitespaces allowed within the Javascript ob-
fuscated data { 1:65535 }
• bool http_inspect.normalize_javascript = false: normalize javascript in response bodies
• bool http_inspect.normalize_utf = true: normalize charset utf encodings in response bodies
• int http_inspect.oversize_dir_length = 300: maximum length for URL directory { 1:65535 }
• bool http_inspect.percent_u = false: normalize %uNNNN and %UNNNN encodings
• bool http_inspect.plus_to_space = true: replace + with <sp> when normalizing URIs
• int http_inspect.print_amount = 1200: number of characters to print from a Field { 1:1000000 }
• bool http_inspect.print_hex = false: nonprinting characters printed in [HH] format instead of using an asterisk
• int http_inspect.request_depth = -1: maximum request message body bytes to examine (-1 no limit) { -1: }
• int http_inspect.response_depth = -1: maximum response message body bytes to examine (-1 no limit) { -1: }
• bool http_inspect.show_pegs = true: display peg counts with test output
• bool http_inspect.show_scan = false: display scanned segments
• bool http_inspect.simplify_path = true: reduce URI directory path to simplest form
• bool http_inspect.test_input = false: read HTTP messages from text file
• bool http_inspect.test_output = false: print out HTTP section data
• bool http_inspect.unzip = true: decompress gzip and deflate message bodies
• bool http_inspect.utf8_bare_byte = false: when doing UTF-8 character normalization include bytes that were not percent
encoded
• bool http_inspect.utf8 = true: normalize 2-byte and 3-byte UTF-8 characters to a single byte
• implied http_method.with_body: parts of this rule examine HTTP message body
• implied http_method.with_trailer: parts of this rule examine HTTP message trailers
• implied http_raw_cookie.request: match against the cookie from the request message even when examining the response
Snort 3 User Manual 208 / 284
• implied http_raw_cookie.with_body: parts of this rule examine HTTP message body
• implied http_raw_cookie.with_trailer: parts of this rule examine HTTP message trailers
• implied http_raw_header.request: match against the headers from the request message even when examining the response
• implied http_raw_header.with_body: parts of this rule examine HTTP message body
• implied http_raw_header.with_trailer: parts of this rule examine HTTP message trailers
• implied http_raw_request.with_body: parts of this rule examine HTTP message body
• implied http_raw_request.with_trailer: parts of this rule examine HTTP message trailers
• implied http_raw_status.with_body: parts of this rule examine HTTP message body
• implied http_raw_status.with_trailer: parts of this rule examine HTTP message trailers
• implied http_raw_trailer.request: match against the trailers from the request message even when examining the response
• implied http_raw_trailer.with_body: parts of this rule examine HTTP response message body (must be combined with
request)
• implied http_raw_trailer.with_header: parts of this rule examine HTTP response message headers (must be combined with
request)
• implied http_raw_uri.fragment: match against fragment section of URI only
• implied http_raw_uri.host: match against host section of URI only
• implied http_raw_uri.path: match against path section of URI only
• implied http_raw_uri.port: match against port section of URI only
• implied http_raw_uri.query: match against query section of URI only
• implied http_raw_uri.scheme: match against scheme section of URI only
• implied http_raw_uri.with_body: parts of this rule examine HTTP message body
• implied http_raw_uri.with_trailer: parts of this rule examine HTTP message trailers
• implied http_stat_code.with_body: parts of this rule examine HTTP message body
• implied http_stat_code.with_trailer: parts of this rule examine HTTP message trailers
• implied http_stat_msg.with_body: parts of this rule examine HTTP message body
• implied http_stat_msg.with_trailer: parts of this rule examine HTTP message trailers
• string http_trailer.field: restrict to given trailer
• implied http_trailer.request: match against the trailers from the request message even when examining the response
• implied http_trailer.with_body: parts of this rule examine HTTP message body (must be combined with request)
• implied http_trailer.with_header: parts of this rule examine HTTP response message headers (must be combined with re-
quest)
• implied http_true_ip.with_body: parts of this rule examine HTTP message body
• implied http_true_ip.with_trailer: parts of this rule examine HTTP message trailers
• implied http_uri.fragment: match against fragment section of URI only
• implied http_uri.host: match against host section of URI only
• implied http_uri.path: match against path section of URI only
Snort 3 User Manual 209 / 284
• implied http_uri.port: match against port section of URI only
• implied http_uri.query: match against query section of URI only
• implied http_uri.scheme: match against scheme section of URI only
• implied http_uri.with_body: parts of this rule examine HTTP message body
• implied http_uri.with_trailer: parts of this rule examine HTTP message trailers
• implied http_version.request: match against the version from the request message even when examining the response
• implied http_version.with_body: parts of this rule examine HTTP message body
• implied http_version.with_trailer: parts of this rule examine HTTP message trailers
• interval icmp_id.~range: check if ICMP ID is in given range { 0:65535 }
• interval icmp_seq.~range: check if ICMP sequence number is in given range { 0:65535 }
• interval icode.~range: check if ICMP code is in given range is { 0:255 }
• interval id.~range: check if the IP ID is in the given range { 0: }
• int imap.b64_decode_depth = 1460: base64 decoding depth { -1:65535 }
• int imap.bitenc_decode_depth = 1460: non-Encoded MIME attachment extraction depth { -1:65535 }
• int imap.qp_decode_depth = 1460: quoted Printable decoding depth { -1:65535 }
• int imap.uu_decode_depth = 1460: Unix-to-Unix decoding depth { -1:65535 }
• int inspection.id = 0: correlate policy and events with other items in configuration { 0:65535 }
• enum inspection.mode = inline-test: set policy mode { inline | inline-test }
• string inspection.uuid: correlate events by uuid
• select ipopts.~opt: output format { rr|eol|nop|ts|sec|esec|lsrr|lsrre|ssrr|satid|any }
• string ip_proto.~proto: [!|>|<] name or number
• bool ips.enable_builtin_rules = false: enable events from builtin rules w/o stubs
• int ips.id = 0: correlate unified2 events with configuration { 0:65535 }
• string ips.include: legacy snort rules and includes
• enum ips.mode: set policy mode { tap | inline | inline-test }
• string ips.rules: snort rules and includes
• string ips.uuid = 00000000-0000-0000-0000-000000000000: IPS policy uuid
• string isdataat.~length: num | !num
• implied isdataat.relative: offset from cursor instead of start of buffer
• interval itype.~range: check if ICMP type is in given range { 0:255 }
• enum latency.packet.action = none: event action if packet times out and is fastpathed { none | alert | log | alert_and_log }
• bool latency.packet.fastpath = false: fastpath expensive packets (max_time exceeded)
• int latency.packet.max_time = 500: set timeout for packet latency thresholding (usec) { 0: }
• enum latency.rule.action = none: event action for rule latency enable and suspend events { none | alert | log | alert_and_log }
Snort 3 User Manual 210 / 284
• int latency.rule.max_suspend_time = 30000: set max time for suspending a rule (ms, 0 means permanently disable rule) { 0:
}
• int latency.rule.max_time = 500: set timeout for rule evaluation (usec) { 0: }
• bool latency.rule.suspend = false: temporarily suspend expensive rules
• int latency.rule.suspend_threshold = 5: set threshold for number of timeouts before suspending a rule { 1: }
• bool log_codecs.file = false: output to log_codecs.txt instead of stdout
• bool log_codecs.msg = false: include alert msg
• bool log_hext.file = false: output to log_hext.txt instead of stdout
• int log_hext.limit = 0: set maximum size in MB before rollover (0 is unlimited) { 0: }
• bool log_hext.raw = false: output all full packets if true, else just TCP payload
• int log_hext.width = 20: set line width (0 is unlimited) { 0: }
• int log_pcap.limit = 0: set maximum size in MB before rollover (0 is unlimited) { 0: }
• string md5.~hash: data to match
• int md5.length: number of octets in plain text { 1:65535 }
• string md5.offset: var or number of bytes from start of buffer to start search
• implied md5.relative = false: offset from cursor instead of start of buffer
• int memory.cap = 0: set the per-packet-thread cap on memory (bytes, 0 to disable) { 0: }
• bool memory.soft = false: always succeed in allocating memory, even if above the cap
• int memory.threshold = 0: set the per-packet-thread threshold for preemptive cleanup actions (percent, 0 to disable) { 0: }
• string metadata.*: comma-separated list of arbitrary name value pairs
• string modbus_func.~: function code to match
• int modbus_unit.~: Modbus unit ID { 0:255 }
• bool mpls.enable_mpls_multicast = false: enables support for MPLS multicast
• bool mpls.enable_mpls_overlapping_ip = false: enable if private network addresses overlap and must be differentiated by
MPLS label(s)
• int mpls.max_mpls_stack_depth = -1: set MPLS stack depth { -1: }
• enum mpls.mpls_payload_type = ip4: set encapsulated payload type { eth | ip4 | ip6 }
• string msg.~: message describing rule
• interval mss.~range: check if TCP MSS is in given range { 0:65535 }
• multi network.checksum_drop = none: drop if checksum is bad { all | ip | noip | tcp | notcp | udp | noudp | icmp | noicmp |
none }
• multi network.checksum_eval = none: checksums to verify { all | ip | noip | tcp | notcp | udp | noudp | icmp | noicmp | none }
• bool network.decode_drops = false: enable dropping of packets by the decoder
• int network.id = 0: correlate unified2 events with configuration { 0:65535 }
• int network.layers = 40: the maximum number of protocols that Snort can correctly decode { 3:255 }
Snort 3 User Manual 211 / 284
• int network.max_ip6_extensions = 0: the maximum number of IP6 options Snort will process for a given IPv6 layer before
raising 116:456 (0 = unlimited) { 0:255 }
• int network.max_ip_layers = 0: the maximum number of IP layers Snort will process for a given packet before raising 116:293
(0 = unlimited) { 0:255 }
• int network.min_ttl = 1: alert / normalize packets with lower TTL / hop limit (you must enable rules and / or normalization
also) { 1:255 }
• int network.new_ttl = 1: use this value for responses and when normalizing { 1:255 }
• bool normalizer.icmp4 = false: clear reserved flag
• bool normalizer.icmp6 = false: clear reserved flag
• bool normalizer.ip4.base = true: clear options
• bool normalizer.ip4.df = false: clear don’t frag flag
• bool normalizer.ip4.rf = false: clear reserved flag
• bool normalizer.ip4.tos = false: clear tos / differentiated services byte
• bool normalizer.ip4.trim = false: truncate excess payload beyond datagram length
• bool normalizer.ip6 = false: clear reserved flag
• string normalizer.tcp.allow_codes: don’t clear given option codes
• multi normalizer.tcp.allow_names: don’t clear given option names { sack | echo | partial_order | conn_count | alt_checksum |
md5 }
• bool normalizer.tcp.base = true: clear reserved bits and option padding and fix urgent pointer / flags issues
• bool normalizer.tcp.block = true: allow packet drops during TCP normalization
• select normalizer.tcp.ecn = off: clear ecn for all packets | sessions w/o ecn setup { off | packet | stream }
• bool normalizer.tcp.ips = false: ensure consistency in retransmitted data
• bool normalizer.tcp.opts = true: clear all options except mss, wscale, timestamp, and any explicitly allowed
• bool normalizer.tcp.pad = true: clear any option padding bytes
• bool normalizer.tcp.req_pay = true: clear the urgent pointer and the urgent flag if there is no payload
• bool normalizer.tcp.req_urg = true: clear the urgent pointer if the urgent flag is not set
• bool normalizer.tcp.req_urp = true: clear the urgent flag if the urgent pointer is not set
• bool normalizer.tcp.rsv = true: clear the reserved bits in the TCP header
• bool normalizer.tcp.trim = false: enable all of the TCP trim options
• bool normalizer.tcp.trim_mss = false: trim data to MSS
• bool normalizer.tcp.trim_rst = false: remove any data from RST packet
• bool normalizer.tcp.trim_syn = false: remove data on SYN
• bool normalizer.tcp.trim_win = false: trim data to window
• bool normalizer.tcp.urp = true: adjust urgent pointer if beyond segment length
• bool output.dump_chars_only = false: turns on character dumps (same as -C)
• bool output.dump_payload = false: dumps application layer (same as -d)
Snort 3 User Manual 212 / 284
• bool output.dump_payload_verbose = false: dumps raw packet starting at link layer (same as -X)
• bool output.enable_packet_trace = false: enable summary output of state that determined packet verdict
• int output.event_trace.max_data = 0: maximum amount of packet data to capture { 0:65535 }
• string output.logdir = .: where to put log files (same as -l)
• bool output.obfuscate = false: obfuscate the logged IP addresses (same as -O)
• bool output.obfuscate_pii = false: mask all but the last 4 characters of credit card and social security numbers
• bool output.quiet = false: suppress non-fatal information (still show alerts, same as -q)
• bool output.show_year = false: include year in timestamp in the alert and log files (same as -y)
• int output.tagged_packet_limit = 256: maximum number of packets tagged for non-packet metrics { 0: }
• bool output.verbose = false: be verbose (same as -v)
• bool output.wide_hex_dump = true: output 20 bytes per lines instead of 16 when dumping buffers
• bool packet_capture.enable = false: initially enable packet dumping
• string packet_capture.filter: bpf filter to use for packet dump
• bool packets.address_space_agnostic = false: determines whether DAQ address space info is used to track fragments and
connections
• string packets.bpf_file: file with BPF to select traffic for Snort
• int packets.limit = 0: maximum number of packets to process before stopping (0 is unlimited) { 0: }
• int packets.skip = 0: number of packets to skip before before processing { 0: }
• bool packets.vlan_agnostic = false: determines whether VLAN info is used to track fragments and connections
• string pcre.~re: Snort regular expression
• bool perf_monitor.base = true: enable base statistics { nullptr }
• bool perf_monitor.cpu = false: enable cpu statistics { nullptr }
• bool perf_monitor.flow = false: enable traffic statistics
• bool perf_monitor.flow_ip = false: enable statistics on host pairs
• int perf_monitor.flow_ip_memcap = 52428800: maximum memory in bytes for flow tracking { 8200: }
• int perf_monitor.flow_ports = 1023: maximum ports to track { 0:65535 }
• enum perf_monitor.format = csv: output format for stats { csv | text | json | flatbuffers }
• int perf_monitor.max_file_size = 1073741824: files will be rolled over if they exceed this size { 4096: }
• string perf_monitor.modules[].name: name of the module
• string perf_monitor.modules[].pegs: list of statistics to track or empty for all counters
• enum perf_monitor.output = file: output location for stats { file | console }
• int perf_monitor.packets = 10000: minimum packets to report { 0: }
• int perf_monitor.seconds = 60: report interval { 1: }
• bool perf_monitor.summary = false: output summary at shutdown
• interval pkt_num.~range: check if packet number is in given range { 1: }
Snort 3 User Manual 213 / 284
• int pop.b64_decode_depth = 1460: base64 decoding depth { -1:65535 }
• int pop.bitenc_decode_depth = 1460: Non-Encoded MIME attachment extraction depth { -1:65535 }
• int pop.qp_decode_depth = 1460: Quoted Printable decoding depth { -1:65535 }
• int pop.uu_decode_depth = 1460: Unix-to-Unix decoding depth { -1:65535 }
• bool port_scan.alert_all = false: alert on all events over threshold within window if true; else alert on first only
• int port_scan.icmp_sweep.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.icmp_sweep.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.icmp_sweep.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.icmp_sweep.scans = 100: scan attempts { 0: }
• int port_scan.icmp_window = 0: detection interval for all ICMP scans { 0: }
• string port_scan.ignore_scanned: list of CIDRs with optional ports to ignore if the destination of scan alerts
• string port_scan.ignore_scanners: list of CIDRs with optional ports to ignore if the source of scan alerts
• bool port_scan.include_midstream = false: list of CIDRs with optional ports
• int port_scan.ip_decoy.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.ip_decoy.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.ip_decoy.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.ip_decoy.scans = 100: scan attempts { 0: }
• int port_scan.ip_dist.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.ip_dist.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.ip_dist.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.ip_dist.scans = 100: scan attempts { 0: }
• int port_scan.ip_proto.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.ip_proto.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.ip_proto.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.ip_proto.scans = 100: scan attempts { 0: }
• int port_scan.ip_sweep.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.ip_sweep.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.ip_sweep.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.ip_sweep.scans = 100: scan attempts { 0: }
• int port_scan.ip_window = 0: detection interval for all IP scans { 0: }
• int port_scan.memcap = 1048576: maximum tracker memory in bytes { 1: }
• multi port_scan.protos = all: choose the protocols to monitor { tcp | udp | icmp | ip | all }
• multi port_scan.scan_types = all: choose type of scans to look for { portscan | portsweep | decoy_portscan | distributed_portscan
| all }
• int port_scan.tcp_decoy.nets = 25: number of times address changed from prior attempt { 0: }
Snort 3 User Manual 214 / 284
• int port_scan.tcp_decoy.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.tcp_decoy.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.tcp_decoy.scans = 100: scan attempts { 0: }
• int port_scan.tcp_dist.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.tcp_dist.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.tcp_dist.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.tcp_dist.scans = 100: scan attempts { 0: }
• int port_scan.tcp_ports.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.tcp_ports.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.tcp_ports.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.tcp_ports.scans = 100: scan attempts { 0: }
• int port_scan.tcp_sweep.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.tcp_sweep.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.tcp_sweep.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.tcp_sweep.scans = 100: scan attempts { 0: }
• int port_scan.tcp_window = 0: detection interval for all TCP scans { 0: }
• int port_scan.udp_decoy.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.udp_decoy.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.udp_decoy.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.udp_decoy.scans = 100: scan attempts { 0: }
• int port_scan.udp_dist.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.udp_dist.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.udp_dist.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.udp_dist.scans = 100: scan attempts { 0: }
• int port_scan.udp_ports.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.udp_ports.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.udp_ports.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.udp_ports.scans = 100: scan attempts { 0: }
• int port_scan.udp_sweep.nets = 25: number of times address changed from prior attempt { 0: }
• int port_scan.udp_sweep.ports = 25: number of times port (or proto) changed from prior attempt { 0: }
• int port_scan.udp_sweep.rejects = 15: scan attempts with negative response { 0: }
• int port_scan.udp_sweep.scans = 100: scan attempts { 0: }
• int port_scan.udp_window = 0: detection interval for all UDP scans { 0: }
• string port_scan.watch_ip: list of CIDRs with optional ports to watch
• int priority.~: relative severity level; 1 is highest priority { 1: }
Snort 3 User Manual 215 / 284
• string process.chroot: set chroot directory (same as -t)
• bool process.daemon = false: fork as a daemon (same as -D)
• bool process.dirty_pig = false: shutdown without internal cleanup
• string process.set_gid: set group ID (same as -g)
• string process.set_uid: set user ID (same as -u)
• string process.threads[].cpuset: pin the associated thread to this cpuset
• int process.threads[].thread = 0: set cpu affinity for the <cur_thread_num> thread that runs { 0: }
• string process.umask: set process umask (same as -m)
• bool process.utc = false: use UTC instead of local time for timestamps
• int profiler.memory.count = 0: limit results to count items per level (0 = no limit) { 0: }
• int profiler.memory.max_depth = -1: limit depth to max_depth (-1 = no limit) { -1: }
• bool profiler.memory.show = true: show module memory profile stats
• enum profiler.memory.sort = total_used: sort by given field { none | allocations | total_used | avg_allocation }
• int profiler.modules.count = 0: limit results to count items per level (0 = no limit) { 0: }
• int profiler.modules.max_depth = -1: limit depth to max_depth (-1 = no limit) { -1: }
• bool profiler.modules.show = true: show module time profile stats
• enum profiler.modules.sort = total_time: sort by given field { none | checks | avg_check | total_time }
• int profiler.rules.count = 0: print results to given level (0 = all) { 0: }
• bool profiler.rules.show = true: show rule time profile stats
• enum profiler.rules.sort = total_time: sort by given field { none | checks | avg_check | total_time | matches | no_matches |
avg_match | avg_no_match }
• string rate_filter[].apply_to: restrict filter to these addresses according to track
• int rate_filter[].count = 1: number of events in interval before tripping { 0: }
• int rate_filter[].gid = 1: rule generator ID { 0: }
• enum rate_filter[].new_action = alert: take this action on future hits until timeout { log | pass | alert | drop | block | reset }
• int rate_filter[].seconds = 1: count interval { 0: }
• int rate_filter[].sid = 1: rule signature ID { 0: }
• int rate_filter[].timeout = 1: count interval { 0: }
• enum rate_filter[].track = by_src: filter only matching source or destination addresses { by_src | by_dst | by_rule }
• bool react.msg = false: use rule msg in response page instead of default message
• string react.page: file containing HTTP response (headers and body)
• string reference.~id: reference id
• string reference.~scheme: reference scheme
• string references[].name: name used with reference rule option
• string references[].url: where this reference is defined
Snort 3 User Manual 216 / 284
• implied regex.dotall: matching a . will not exclude newlines
• implied regex.fast_pattern: use this content in the fast pattern matcher instead of the content selected by default
• implied regex.multiline: ˆ and $ anchors match any newlines in data
• implied regex.nocase: case insensitive match
• string regex.~re: hyperscan regular expression
• implied regex.relative: start search from end of last match instead of start of buffer
• bool reg_test.test_daq_retry = true: test daq packet retry feature
• enum reject.control: send ICMP unreachable(s) { network|host|port|all }
• enum reject.reset: send TCP reset to one or both ends { source|dest|both }
• string rem.~: comment
• string replace.~: byte code to replace with
• string reputation.blacklist: blacklist file name with IP lists
• int reputation.memcap = 500: maximum total MB of memory allocated { 1:4095 }
• enum reputation.nested_ip = inner: IP to use when there is IP encapsulation { inner|outer|all }
• enum reputation.priority = whitelist: defines priority when there is a decision conflict during run-time { blacklist|whitelist }
• bool reputation.scan_local = false: inspect local address defined in RFC 1918
• string reputation.whitelist: whitelist file name with IP lists
• enum reputation.white = unblack: specify the meaning of whitelist { unblack|trust }
• int rev.~: revision { 1: }
• bool rewrite.disable_replace = false: disable replace of packet contents with rewrite rules
• int rpc.~app: application number
• string rpc.~proc: procedure number or * for any
• string rpc.~ver: version number or * for any
• bool rule_state.enable = true: enable or disable rule in all policies
• int rule_state.gid = 0: rule generator ID { 0: }
• int rule_state.sid = 0: rule signature ID { 0: }
• string sd_pattern.~pattern: The pattern to search for
• int sd_pattern.threshold: number of matches before alerting { 1 }
• int search_engine.bleedover_port_limit = 1024: maximum ports in rule before demotion to any-any port group { 1: }
• bool search_engine.bleedover_warnings_enabled = false: print warning if a rule is demoted to any-any port group
• bool search_engine.debug = false: print verbose fast pattern info
• bool search_engine.debug_print_nocontent_rule_tests = false: print rule group info during packet evaluation
• bool search_engine.debug_print_rule_group_build_details = false: print rule group info during compilation
• bool search_engine.debug_print_rule_groups_compiled = false: prints compiled rule group information
• bool search_engine.debug_print_rule_groups_uncompiled = false: prints uncompiled rule group information
Snort 3 User Manual 217 / 284
• bool search_engine.detect_raw_tcp = true: detect on TCP payload before reassembly
• bool search_engine.enable_single_rule_group = false: put all rules into one group
• int search_engine.max_pattern_len = 0: truncate patterns when compiling into state machine (0 means no maximum) { 0: }
• int search_engine.max_queue_events = 5: maximum number of matching fast pattern states to queue per packet { 2:100 }
• dynamic search_engine.search_method = ac_bnfa: set fast pattern algorithm - choose available search engine { ac_banded |
ac_bnfa | ac_full | ac_sparse | ac_sparse_bands | ac_std | hyperscan | lowmem }
• bool search_engine.search_optimize = true: tweak state machine construction for better performance
• bool search_engine.show_fast_patterns = false: print fast pattern info for each rule
• bool search_engine.split_any_any = true: evaluate any-any rules separately to save memory
• interval seq.~range: check if TCP sequence number is in given range { 0: }
• string service.*: one or more comma-separated service names
• enum session.~mode: output format { printable|binary|all }
• string sha256.~hash: data to match
• int sha256.length: number of octets in plain text { 1:65535 }
• string sha256.offset: var or number of bytes from start of buffer to start search
• implied sha256.relative = false: offset from cursor instead of start of buffer
• string sha512.~hash: data to match
• int sha512.length: number of octets in plain text { 1:65535 }
• string sha512.offset: var or number of bytes from start of buffer to start search
• implied sha512.relative = false: offset from cursor instead of start of buffer
• string side_channel.connector: connector handle
• string side_channel.connectors[].connector: connector handle
• bit_list side_channel.ports: side channel message port list { 65535 }
• int sid.~: signature id { 1: }
• bool sip.ignore_call_channel = false: enables the support for ignoring audio/video data channel
• int sip.max_call_id_len = 256: maximum call id field size { 0:65535 }
• int sip.max_contact_len = 256: maximum contact field size { 0:65535 }
• int sip.max_content_len = 1024: maximum content length of the message body { 0:65535 }
• int sip.max_dialogs = 4: maximum number of dialogs within one stream session { 1:4194303 }
• int sip.max_from_len = 256: maximum from field size { 0:65535 }
• int sip.max_requestName_len = 20: maximum request name field size { 0:65535 }
• int sip.max_to_len = 256: maximum to field size { 0:65535 }
• int sip.max_uri_len = 256: maximum request uri field size { 0:65535 }
• int sip.max_via_len = 1024: maximum via field size { 0:65535 }
• string sip_method.*method: sip method
Snort 3 User Manual 218 / 284
• string sip.methods = invite cancel ack bye register options: list of methods to check in SIP messages
• int sip_stat_code.*code: stat code { 1:999 }
• string smtp.alt_max_command_line_len[].command: command string
• int smtp.alt_max_command_line_len[].length = 0: specify non-default maximum for command { 0: }
• string smtp.auth_cmds: commands that initiate an authentication exchange
• int smtp.b64_decode_depth = 25: depth used to decode the base64 encoded MIME attachments { -1:65535 }
• string smtp.binary_data_cmds: commands that initiate sending of data and use a length value after the command
• int smtp.bitenc_decode_depth = 25: depth used to extract the non-encoded MIME attachments { -1:65535 }
• string smtp.data_cmds: commands that initiate sending of data with an end of data delimiter
• int smtp.email_hdrs_log_depth = 1464: depth for logging email headers { 0:20480 }
• bool smtp.ignore_data = false: ignore data section of mail
• bool smtp.ignore_tls_data = false: ignore TLS-encrypted data when processing rules
• string smtp.invalid_cmds: alert if this command is sent from client side
• bool smtp.log_email_hdrs = false: log the SMTP email headers extracted from SMTP data
• bool smtp.log_filename = false: log the MIME attachment filenames extracted from the Content-Disposition header within
the MIME body
• bool smtp.log_mailfrom = false: log the sender’s email address extracted from the MAIL FROM command
• bool smtp.log_rcptto = false: log the recipient’s email address extracted from the RCPT TO command
• int smtp.max_auth_command_line_len = 1000: max auth command Line Length { 0:65535 }
• int smtp.max_command_line_len = 0: max Command Line Length { 0:65535 }
• int smtp.max_header_line_len = 0: max SMTP DATA header line { 0:65535 }
• int smtp.max_response_line_len = 0: max SMTP response line { 0:65535 }
• string smtp.normalize_cmds: list of commands to normalize
• enum smtp.normalize = none: turns on/off normalization { none | cmds | all }
• int smtp.qp_decode_depth = 25: quoted-Printable decoding depth { -1:65535 }
• int smtp.uu_decode_depth = 25: unix-to-Unix decoding depth { -1:65535 }
• string smtp.valid_cmds: list of valid commands
• enum smtp.xlink2state = alert: enable/disable xlink2state alert { disable | alert | drop }
• implied snort.--alert-before-pass: process alert, drop, sdrop, or reject before pass; default is pass before alert, drop,. . .
• string snort.-A: <mode> set alert mode: none, cmg, or alert_*
• addr snort.-B = 255.255.255.255/32: <mask> obfuscated IP addresses in alerts and packet dumps using CIDR mask
• string snort.--bpf: <filter options> are standard BPF options, as seen in TCPDump
• string snort.--c2x: output hex for given char (see also --x2c)
• string snort.--catch-test: comma separated list of cat unit test tags or all
• string snort.-c: <conf> use this configuration
Snort 3 User Manual 219 / 284
• string snort.--control-socket: <file> to create unix socket
• implied snort.-C: print out payloads with character data only (no hex)
• implied snort.--create-pidfile: create PID file, even when not in Daemon mode
• string snort.--daq-dir: <dir> tell snort where to find desired DAQ
• implied snort.--daq-list: list packet acquisition modules available in optional dir, default is static modules only
• string snort.--daq: <type> select packet acquisition module (default is pcap)
• string snort.--daq-var: <name=value> specify extra DAQ configuration variable
• implied snort.-d: dump the Application Layer
• implied snort.--dirty-pig: don’t flush packets on shutdown
• implied snort.-D: run Snort in background (daemon) mode
• string snort.--dump-builtin-rules: [<module prefix>] output stub rules for selected modules { (optional) }
• string snort.--dump-defaults: [<module prefix>] output module defaults in Lua format { (optional) }
• implied snort.--dump-dynamic-rules: output stub rules for all loaded rules libraries
• implied snort.--dump-version: output the version, the whole version, and only the version
• implied snort.-e: display the second layer header info
• implied snort.--enable-inline-test: enable Inline-Test Mode Operation
• implied snort.-f: turn off fflush() calls after binary log writes
• int snort.-G: <0xid> (same as --logid) { 0:65535 }
• implied snort.--gen-msg-map: dump builtin rules in gen-msg.map format for use by other tools
• string snort.-g: <gname> run snort gid as <gname> group (or gid) after initialization
• string snort.--help-commands: [<module prefix>] output matching commands { (optional) }
• string snort.--help-config: [<module prefix>] output matching config options { (optional) }
• string snort.--help-counts: [<module prefix>] output matching peg counts { (optional) }
• implied snort.--help: list command line options
• string snort.--help-module: <module> output description of given module
• implied snort.--help-modules: list all available modules with brief help
• string snort.--help-options: [<option prefix>] output matching command line option quick help (same as -?) { (optional) }
• implied snort.--help-plugins: list all available plugins with brief help
• implied snort.--help-signals: dump available control signals
• implied snort.-H: make hash tables deterministic
• int snort.--id-offset = 0: offset to add to instance IDs when logging to files { 0:65535 }
• implied snort.--id-subdir: create/use instance subdirectories in logdir instead of instance filename prefix
• implied snort.--id-zero: use id prefix / subdirectory even with one packet thread
• string snort.-i: <iface>. . . list of interfaces
• port snort.-j: <port> to listen for Telnet connections
Snort 3 User Manual 220 / 284
• enum snort.-k = all: <mode> checksum mode; default is all { all|noip|notcp|noudp|noicmp|none }
• implied snort.--list-buffers: output available inspection buffers
• string snort.--list-builtin: [<module prefix>] output matching builtin rules { (optional) }
• string snort.--list-gids: [<module prefix>] output matching generators { (optional) }
• string snort.--list-modules: [<module type>] list all known modules of given type { (optional) }
• implied snort.--list-plugins: list all known plugins
• string snort.-l: <logdir> log to this directory instead of current directory
• string snort.-L: <mode> logging mode (none, dump, pcap, or log_*)
• int snort.--logid: <0xid> log Identifier to uniquely id events for multiple snorts (same as -G) { 0:65535 }
• string snort.--lua: <chunk> extend/override conf with chunk; may be repeated
• implied snort.--markup: output help in asciidoc compatible format
• int snort.--max-packet-threads = 1: <count> configure maximum number of packet threads (same as -z) { 0: }
• implied snort.--mem-check: like -T but also compile search engines
• implied snort.-M: log messages to syslog (not alerts)
• int snort.-m: <umask> set umask = <umask> { 0: }
• int snort.-n: <count> stop after count packets { 0: }
• implied snort.--nolock-pidfile: do not try to lock Snort PID file
• implied snort.--nostamps: don’t include timestamps in log file names
• implied snort.-O: obfuscate the logged IP addresses
• string snort.-?: <option prefix> output matching command line option quick help (same as --help-options) { (optional) }
• implied snort.--parsing-follows-files: parse relative paths from the perspective of the current configuration file
• implied snort.--pause: wait for resume/quit command before processing packets/terminating
• string snort.--pcap-dir: <dir> a directory to recurse to look for pcaps - read mode is implied
• string snort.--pcap-file: <file> file that contains a list of pcaps to read - read mode is implied
• string snort.--pcap-filter: <filter> filter to apply when getting pcaps from file or directory
• string snort.--pcap-list: <list> a space separated list of pcaps to read - read mode is implied
• int snort.--pcap-loop: <count> read all pcaps <count> times; 0 will read until Snort is terminated { -1: }
• implied snort.--pcap-no-filter: reset to use no filter when getting pcaps from file or directory
• implied snort.--pcap-reload: if reading multiple pcaps, reload snort config between pcaps
• implied snort.--pcap-show: print a line saying what pcap is currently being read
• implied snort.--pedantic: warnings are fatal
• implied snort.--piglet: enable piglet test harness mode
• string snort.--plugin-path: <path> where to find plugins
• implied snort.--process-all-events: process all action groups
• implied snort.-Q: enable inline mode operation
Snort 3 User Manual 221 / 284
• implied snort.-q: quiet mode - Don’t show banner and status report
• string snort.-r: <pcap>. . . (same as --pcap-list)
• string snort.-R: <rules> include this rules file in the default policy
• string snort.--rule: <rules> to be added to configuration; may be repeated
• implied snort.--rule-to-hex: output so rule header to stdout for text rule on stdin
• implied snort.--rule-to-text: output plain so rule header to stdout for text rule on stdin
• string snort.--run-prefix: <pfx> prepend this to each output file
• int snort.-s = 1514: <snap> (same as --snaplen); default is 1514 { 68:65535 }
• string snort.--script-path: <path> to a luajit script or directory containing luajit scripts
• implied snort.--shell: enable the interactive command line
• implied snort.--show-plugins: list module and plugin versions
• int snort.--skip: <n> skip 1st n packets { 0: }
• int snort.--snaplen = 1514: <snap> set snaplen of packet (same as -s) { 68:65535 }
• implied snort.--stdin-rules: read rules from stdin until EOF or a line starting with END is read
• string snort.-S: <x=v> set config variable x equal to value v
• string snort.-t: <dir> chroots process to <dir> after initialization
• implied snort.--treat-drop-as-alert: converts drop, sdrop, and reject rules into alert rules during startup
• implied snort.--treat-drop-as-ignore: use drop, sdrop, and reject rules to ignore session traffic when not inline
• implied snort.-T: test and report on the current Snort configuration
• string snort.-u: <uname> run snort as <uname> or <uid> after initialization
• implied snort.-U: use UTC for timestamps
• implied snort.-v: be verbose
• implied snort.--version: show version number (same as -V)
• implied snort.-V: (same as --version)
• implied snort.--warn-all: enable all warnings
• implied snort.--warn-conf: warn about configuration issues
• implied snort.--warn-daq: warn about DAQ issues, usually related to mode
• implied snort.--warn-flowbits: warn about flowbits that are checked but not set and vice-versa
• implied snort.--warn-hosts: warn about host table issues
• implied snort.--warn-plugins: warn about issues that prevent plugins from loading
• implied snort.--warn-rules: warn about duplicate rules and rule parsing issues
• implied snort.--warn-scripts: warn about issues discovered while processing Lua scripts
• implied snort.--warn-symbols: warn about unknown symbols in your Lua config
• implied snort.--warn-vars: warn about variable definition and usage issues
• implied snort.-W: lists available interfaces
Snort 3 User Manual 222 / 284
• int snort.--x2c: output ASCII char for given hex (see also --c2x)
• string snort.--x2s: output ASCII string for given byte code (see also --x2c)
• implied snort.-X: dump the raw packet data starting at the link layer
• implied snort.-x: same as --pedantic
• implied snort.-y: include year in timestamp in the alert and log files
• int snort.-z = 1: <count> maximum number of packet threads (same as --max-packet-threads); 0 gets the number of CPU cores
reported by the system; default is 1 { 0: }
• string so.~func: name of eval function
• string soid.~: SO rule ID is unique key, eg <gid>_<sid>_<rev> like 3_45678_9
• int ssh.max_client_bytes = 19600: number of unanswered bytes before alerting on challenge-response overflow or CRC32 {
0:65535 }
• int ssh.max_encrypted_packets = 25: ignore session after this many encrypted packets { 0:65535 }
• int ssh.max_server_version_len = 80: limit before alerting on secure CRT server version string overflow { 0:255 }
• int ssl.max_heartbeat_length = 0: maximum length of heartbeat record allowed { 0:65535 }
• implied ssl_state.client_hello: check for client hello
• implied ssl_state.!client_hello: check for records that are not client hello
• implied ssl_state.client_keyx: check for client keyx
• implied ssl_state.!client_keyx: check for records that are not client keyx
• implied ssl_state.!server_hello: check for records that are not server hello
• implied ssl_state.server_hello: check for server hello
• implied ssl_state.!server_keyx: check for records that are not server keyx
• implied ssl_state.server_keyx: check for server keyx
• implied ssl_state.!unknown: check for records that are not unknown
• implied ssl_state.unknown: check for unknown record
• bool ssl.trust_servers = false: disables requirement that application (encrypted) data must be observed on both sides
• implied ssl_version.!sslv2: check for records that are not sslv2
• implied ssl_version.sslv2: check for sslv2
• implied ssl_version.!sslv3: check for records that are not sslv3
• implied ssl_version.sslv3: check for sslv3
• implied ssl_version.!tls1.0: check for records that are not tls1.0
• implied ssl_version.tls1.0: check for tls1.0
• implied ssl_version.!tls1.1: check for records that are not tls1.1
• implied ssl_version.tls1.1: check for tls1.1
• implied ssl_version.!tls1.2: check for records that are not tls1.2
• implied ssl_version.tls1.2: check for tls1.2
• int stream.file_cache.idle_timeout = 180: maximum inactive time before retiring session tracker { 1: }
Snort 3 User Manual 223 / 284
• int stream.file_cache.max_sessions = 128: maximum simultaneous sessions tracked before pruning { 2: }
• int stream.file_cache.pruning_timeout = 30: minimum inactive time before being eligible for pruning { 1: }
• bool stream_file.upload = false: indicate file transfer direction
• int stream.footprint = 0: use zero for production, non-zero for testing at given size (for TCP and user) { 0: }
• int stream.icmp_cache.idle_timeout = 180: maximum inactive time before retiring session tracker { 1: }
• int stream.icmp_cache.max_sessions = 65536: maximum simultaneous sessions tracked before pruning { 2: }
• int stream.icmp_cache.pruning_timeout = 30: minimum inactive time before being eligible for pruning { 1: }
• int stream_icmp.session_timeout = 30: session tracking timeout { 1:86400 }
• int stream.ip_cache.idle_timeout = 180: maximum inactive time before retiring session tracker { 1: }
• int stream.ip_cache.max_sessions = 16384: maximum simultaneous sessions tracked before pruning { 2: }
• int stream.ip_cache.pruning_timeout = 30: minimum inactive time before being eligible for pruning { 1: }
• bool stream.ip_frags_only = false: don’t process non-frag flows
• int stream_ip.max_frags = 8192: maximum number of simultaneous fragments being tracked { 1: }
• int stream_ip.max_overlaps = 0: maximum allowed overlaps per datagram; 0 is unlimited { 0: }
• int stream_ip.min_frag_length = 0: alert if fragment length is below this limit before or after trimming { 0: }
• int stream_ip.min_ttl = 1: discard fragments with TTL below the minimum { 1:255 }
• enum stream_ip.policy = linux: fragment reassembly policy { first | linux | bsd | bsd_right | last | windows | solaris }
• int stream_ip.session_timeout = 30: session tracking timeout { 1:86400 }
• int stream_ip.trace: mask for enabling debug traces in module
• enum stream_reassemble.action: stop or start stream reassembly { disable|enable }
• enum stream_reassemble.direction: action applies to the given direction(s) { client|server|both }
• implied stream_reassemble.fastpath: optionally whitelist the remainder of the session
• implied stream_reassemble.noalert: don’t alert when rule matches
• enum stream_size.~direction: compare applies to the given direction(s) { either|to_server|to_client|both }
• interval stream_size.~range: check if the stream size is in the given range { 0: }
• int stream.tcp_cache.idle_timeout = 3600: maximum inactive time before retiring session tracker { 1: }
• int stream.tcp_cache.max_sessions = 262144: maximum simultaneous sessions tracked before pruning { 2: }
• int stream.tcp_cache.pruning_timeout = 30: minimum inactive time before being eligible for pruning { 1: }
• int stream_tcp.flush_factor = 0: flush upon seeing a drop in segment size after given number of non-decreasing segments {
0: }
• bool stream_tcp.ignore_any_rules = false: process TCP content rules w/o ports only if rules with ports are present
• int stream_tcp.max_pdu = 16384: maximum reassembled PDU size { 1460:32768 }
• int stream_tcp.max_window = 0: maximum allowed TCP window { 0:1073725440 }
• int stream_tcp.overlap_limit = 0: maximum number of allowed overlapping segments per session { 0:255 }
• enum stream_tcp.policy = bsd: determines operating system characteristics like reassembly { first | last | linux | old_linux |
bsd | macos | solaris | irix | hpux11 | hpux10 | windows | win_2003 | vista | proxy }
Snort 3 User Manual 224 / 284
• int stream_tcp.queue_limit.max_bytes = 1048576: don’t queue more than given bytes per session and direction { 0: }
• int stream_tcp.queue_limit.max_segments = 2621: don’t queue more than given segments per session and direction { 0: }
• bool stream_tcp.reassemble_async = true: queue data for reassembly before traffic is seen in both directions
• int stream_tcp.require_3whs = -1: don’t track midstream sessions after given seconds from start up; -1 tracks all { -1:86400
}
• int stream_tcp.session_timeout = 30: session tracking timeout { 1:86400 }
• bool stream_tcp.show_rebuilt_packets = false: enable cmg like output of reassembled packets
• int stream_tcp.small_segments.count = 0: limit number of small segments queued { 0:2048 }
• int stream_tcp.small_segments.maximum_size = 0: limit number of small segments queued { 0:2048 }
• int stream.udp_cache.idle_timeout = 180: maximum inactive time before retiring session tracker { 1: }
• int stream.udp_cache.max_sessions = 131072: maximum simultaneous sessions tracked before pruning { 2: }
• int stream.udp_cache.pruning_timeout = 30: minimum inactive time before being eligible for pruning { 1: }
• bool stream_udp.ignore_any_rules = false: process UDP content rules w/o ports only if rules with ports are present
• int stream_udp.session_timeout = 30: session tracking timeout { 1:86400 }
• int stream.user_cache.idle_timeout = 180: maximum inactive time before retiring session tracker { 1: }
• int stream.user_cache.max_sessions = 1024: maximum simultaneous sessions tracked before pruning { 2: }
• int stream.user_cache.pruning_timeout = 30: minimum inactive time before being eligible for pruning { 1: }
• int stream_user.session_timeout = 30: session tracking timeout { 1:86400 }
• int stream_user.trace: mask for enabling debug traces in module
• int suppress[].gid = 0: rule generator ID { 0: }
• string suppress[].ip: restrict suppression to these addresses according to track
• int suppress[].sid = 0: rule signature ID { 0: }
• enum suppress[].track: suppress only matching source or destination addresses { by_src | by_dst }
• int tag.bytes: tag for this many bytes { 1: }
• enum tag.~: log all packets in session or all packets to or from host { session|host_src|host_dst }
• int tag.packets: tag this many packets { 1: }
• int tag.seconds: tag for this many seconds { 1: }
• enum target.~: indicate the target of the attack { src_ip | dst_ip }
• string tcp_connector.address: address
• port tcp_connector.base_port: base port number
• string tcp_connector.connector: connector name
• enum tcp_connector.setup: stream establishment { call | answer }
• int telnet.ayt_attack_thresh = -1: alert on this number of consecutive Telnet AYT commands { -1: }
• bool telnet.check_encrypted = false: check for end of encryption
• bool telnet.encrypted_traffic = false: check for encrypted Telnet and FTP
Snort 3 User Manual 225 / 284
• bool telnet.normalize = false: eliminate escape sequences
• interval tos.~range: check if IP TOS is in given range { 0:255 }
• interval ttl.~range: check if IP TTL is in the given range { 0:255 }
• bool udp.deep_teredo_inspection = false: look for Teredo on all UDP ports (default is only 3544)
• bool udp.enable_gtp = false: decode GTP encapsulations
• bit_list udp.gtp_ports = 2152 3386: set GTP ports { 65535 }
• bool unified2.legacy_events = false: generate Snort 2.X style events for barnyard2 compatibility
• int unified2.limit = 0: set maximum size in MB before rollover (0 is unlimited) { 0: }
• bool unified2.nostamp = true: append file creation time to name (in Unix Epoch format)
• interval urg.~range: check if tcp urgent offset is in given range { 0:65535 }
• interval window.~range: check if TCP window size is in given range { 0:65535 }
• multi wizard.curses: enable service identification based on internal algorithm { dce_smb | dce_udp | dce_tcp }
• bool wizard.hexes[].client_first = true: which end initiates data transfer
• select wizard.hexes[].proto = tcp: protocol to scan { tcp | udp }
• string wizard.hexes[].service: name of service
• string wizard.hexes[].to_client[].hex: sequence of data with wild chars (?)
• string wizard.hexes[].to_server[].hex: sequence of data with wild chars (?)
• bool wizard.spells[].client_first = true: which end initiates data transfer
• select wizard.spells[].proto = tcp: protocol to scan { tcp | udp }
• string wizard.spells[].service: name of service
• string wizard.spells[].to_client[].spell: sequence of data with wild cards (*)
• string wizard.spells[].to_server[].spell: sequence of data with wild cards (*)
• interval wscale.~range: check if TCP window scale is in given range { 0:65535 }
20.5 Counts
•arp_spoof.packets: total packets (sum)
•back_orifice.packets: total packets (sum)
•binder.allows: allow bindings (sum)
•binder.blocks: block bindings (sum)
•binder.inspects: inspect bindings (sum)
•binder.packets: initial bindings (sum)
•binder.resets: reset bindings (sum)
•daq.allow: total allow verdicts (sum)
•daq.analyzed: total packets analyzed from DAQ (sum)
•daq.blacklist: total blacklist verdicts (sum)
Snort 3 User Manual 226 / 284
•daq.block: total block verdicts (sum)
•daq.dropped: packets dropped (sum)
•daq.filtered: packets filtered out (sum)
•daq.idle: attempts to acquire from DAQ without available packets (sum)
•daq.ignore: total ignore verdicts (sum)
•daq.injected: active responses or replacements (sum)
•daq.internal_blacklist: packets blacklisted internally due to lack of DAQ support (sum)
•daq.internal_whitelist: packets whitelisted internally due to lack of DAQ support (sum)
•daq.outstanding: packets unprocessed (sum)
•daq.pcaps: total files and interfaces processed (sum)
•daq.received: total packets received from DAQ (sum)
•daq.replace: total replace verdicts (sum)
•daq.retry: total retry verdicts (sum)
•daq.rx_bytes: total bytes received (sum)
•daq.skipped: packets skipped at startup (sum)
•daq.whitelist: total whitelist verdicts (sum)
•data_log.packets: total packets (sum)
•dce_http_proxy.http_proxy_session_failures: failed http proxy sessions (sum)
•dce_http_proxy.http_proxy_sessions: successful http proxy sessions (sum)
•dce_http_server.http_server_session_failures: failed http server sessions (sum)
•dce_http_server.http_server_sessions: successful http server sessions (sum)
•dce_smb.alter_context_responses: total connection-oriented alter context responses (sum)
•dce_smb.alter_contexts: total connection-oriented alter contexts (sum)
•dce_smb.auth3s: total connection-oriented auth3s (sum)
•dce_smb.bind_acks: total connection-oriented binds acks (sum)
•dce_smb.bind_naks: total connection-oriented bind naks (sum)
•dce_smb.binds: total connection-oriented binds (sum)
•dce_smb.cancels: total connection-oriented cancels (sum)
•dce_smb.client_frags_reassembled: total connection-oriented client fragments reassembled (sum)
•dce_smb.client_max_fragment_size: connection-oriented client maximum fragment size (sum)
•dce_smb.client_min_fragment_size: connection-oriented client minimum fragment size (sum)
•dce_smb.client_segs_reassembled: total connection-oriented client segments reassembled (sum)
•dce_smb.concurrent_sessions: total concurrent sessions (now)
•dce_smb.events: total events (sum)
•dce_smb.faults: total connection-oriented faults (sum)
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•dce_smb.files_processed: total smb files processed (sum)
•dce_smb.ignored_bytes: total ignored bytes (sum)
•dce_smb.max_concurrent_sessions: maximum concurrent sessions (max)
•dce_smb.max_outstanding_requests: total smb maximum outstanding requests (sum)
•dce_smb.ms_rpc_http_pdus: total connection-oriented MS requests to send RPC over HTTP (sum)
•dce_smb.orphaned: total connection-oriented orphaned (sum)
•dce_smb.other_requests: total connection-oriented other requests (sum)
•dce_smb.other_responses: total connection-oriented other responses (sum)
•dce_smb.packets: total smb packets (sum)
•dce_smb.pdus: total connection-oriented PDUs (sum)
•dce_smb.rejects: total connection-oriented rejects (sum)
•dce_smb.request_fragments: total connection-oriented request fragments (sum)
•dce_smb.requests: total connection-oriented requests (sum)
•dce_smb.response_fragments: total connection-oriented response fragments (sum)
•dce_smb.responses: total connection-oriented responses (sum)
•dce_smb.server_frags_reassembled: total connection-oriented server fragments reassembled (sum)
•dce_smb.server_max_fragment_size: connection-oriented server maximum fragment size (sum)
•dce_smb.server_min_fragment_size: connection-oriented server minimum fragment size (sum)
•dce_smb.server_segs_reassembled: total connection-oriented server segments reassembled (sum)
•dce_smb.sessions: total smb sessions (sum)
•dce_smb.shutdowns: total connection-oriented shutdowns (sum)
•dce_smb.smb_client_segs_reassembled: total smb client segments reassembled (sum)
•dce_smb.smb_server_segs_reassembled: total smb server segments reassembled (sum)
•dce_smb.smbv2_close: total number of SMBv2 close packets seen (sum)
•dce_smb.smbv2_create: total number of SMBv2 create packets seen (sum)
•dce_smb.smbv2_read: total number of SMBv2 read packets seen (sum)
•dce_smb.smbv2_set_info: total number of SMBv2 set info packets seen (sum)
•dce_smb.smbv2_tree_connect: total number of SMBv2 tree connect packets seen (sum)
•dce_smb.smbv2_tree_disconnect: total number of SMBv2 tree disconnect packets seen (sum)
•dce_smb.smbv2_write: total number of SMBv2 write packets seen (sum)
•dce_tcp.alter_context_responses: total connection-oriented alter context responses (sum)
•dce_tcp.alter_contexts: total connection-oriented alter contexts (sum)
•dce_tcp.auth3s: total connection-oriented auth3s (sum)
•dce_tcp.bind_acks: total connection-oriented binds acks (sum)
•dce_tcp.bind_naks: total connection-oriented bind naks (sum)
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•dce_tcp.binds: total connection-oriented binds (sum)
•dce_tcp.cancels: total connection-oriented cancels (sum)
•dce_tcp.client_frags_reassembled: total connection-oriented client fragments reassembled (sum)
•dce_tcp.client_max_fragment_size: connection-oriented client maximum fragment size (sum)
•dce_tcp.client_min_fragment_size: connection-oriented client minimum fragment size (sum)
•dce_tcp.client_segs_reassembled: total connection-oriented client segments reassembled (sum)
•dce_tcp.concurrent_sessions: total concurrent sessions (now)
•dce_tcp.events: total events (sum)
•dce_tcp.faults: total connection-oriented faults (sum)
•dce_tcp.max_concurrent_sessions: maximum concurrent sessions (max)
•dce_tcp.ms_rpc_http_pdus: total connection-oriented MS requests to send RPC over HTTP (sum)
•dce_tcp.orphaned: total connection-oriented orphaned (sum)
•dce_tcp.other_requests: total connection-oriented other requests (sum)
•dce_tcp.other_responses: total connection-oriented other responses (sum)
•dce_tcp.pdus: total connection-oriented PDUs (sum)
•dce_tcp.rejects: total connection-oriented rejects (sum)
•dce_tcp.request_fragments: total connection-oriented request fragments (sum)
•dce_tcp.requests: total connection-oriented requests (sum)
•dce_tcp.response_fragments: total connection-oriented response fragments (sum)
•dce_tcp.responses: total connection-oriented responses (sum)
•dce_tcp.server_frags_reassembled: total connection-oriented server fragments reassembled (sum)
•dce_tcp.server_max_fragment_size: connection-oriented server maximum fragment size (sum)
•dce_tcp.server_min_fragment_size: connection-oriented server minimum fragment size (sum)
•dce_tcp.server_segs_reassembled: total connection-oriented server segments reassembled (sum)
•dce_tcp.shutdowns: total connection-oriented shutdowns (sum)
•dce_tcp.tcp_packets: total tcp packets (sum)
•dce_tcp.tcp_sessions: total tcp sessions (sum)
•dce_udp.acks: total connection-less acks (sum)
•dce_udp.cancel_acks: total connection-less cancel acks (sum)
•dce_udp.cancels: total connection-less cancels (sum)
•dce_udp.client_facks: total connection-less client facks (sum)
•dce_udp.concurrent_sessions: total concurrent sessions (now)
•dce_udp.events: total events (sum)
•dce_udp.faults: total connection-less faults (sum)
•dce_udp.fragments: total connection-less fragments (sum)
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•dce_udp.frags_reassembled: total connection-less fragments reassembled (sum)
•dce_udp.max_concurrent_sessions: maximum concurrent sessions (max)
•dce_udp.max_fragment_size: connection-less maximum fragment size (sum)
•dce_udp.max_seqnum: max connection-less seqnum (sum)
•dce_udp.no_calls: total connection-less no calls (sum)
•dce_udp.other_requests: total connection-less other requests (sum)
•dce_udp.other_responses: total connection-less other responses (sum)
•dce_udp.ping: total connection-less ping (sum)
•dce_udp.rejects: total connection-less rejects (sum)
•dce_udp.requests: total connection-less requests (sum)
•dce_udp.responses: total connection-less responses (sum)
•dce_udp.server_facks: total connection-less server facks (sum)
•dce_udp.udp_packets: total udp packets (sum)
•dce_udp.udp_sessions: total udp sessions (sum)
•dce_udp.working: total connection-less working (sum)
•detection.alert_limit: events previously triggered on same PDU (sum)
•detection.alerts: alerts not including IP reputation (sum)
•detection.alt_searches: alt fast pattern searches in packet data (sum)
•detection.analyzed: packets sent to detection (sum)
•detection.body_searches: fast pattern searches in body buffer (sum)
•detection.cooked_searches: fast pattern searches in cooked packet data (sum)
•detection.event_limit: events filtered (sum)
•detection.file_searches: fast pattern searches in file buffer (sum)
•detection.hard_evals: non-fast pattern rule evaluations (sum)
•detection.header_searches: fast pattern searches in header buffer (sum)
•detection.key_searches: fast pattern searches in key buffer (sum)
•detection.logged: logged packets (sum)
•detection.log_limit: events queued but not logged (sum)
•detection.match_limit: fast pattern matches not processed (sum)
•detection.offloads: fast pattern searches that were offloaded (sum)
•detection.passed: passed packets (sum)
•detection.pkt_searches: fast pattern searches in packet data (sum)
•detection.queue_limit: events not queued because queue full (sum)
•detection.raw_searches: fast pattern searches in raw packet data (sum)
•detection.total_alerts: alerts including IP reputation (sum)
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•dnp3.concurrent_sessions: total concurrent dnp3 sessions (now)
•dnp3.dnp3_application_pdus: total dnp3 application pdus (sum)
•dnp3.dnp3_link_layer_frames: total dnp3 link layer frames (sum)
•dnp3.max_concurrent_sessions: maximum concurrent dnp3 sessions (max)
•dnp3.tcp_pdus: total tcp pdus (sum)
•dnp3.total_packets: total packets (sum)
•dnp3.udp_packets: total udp packets (sum)
•dns.concurrent_sessions: total concurrent dns sessions (now)
•dns.max_concurrent_sessions: maximum concurrent dns sessions (max)
•dns.packets: total packets processed (sum)
•dns.requests: total dns requests (sum)
•dns.responses: total dns responses (sum)
•dpx.packets: total packets (sum)
•file_connector.messages: total messages (sum)
•file_id.cache_failures: number of file cache add failures (sum)
•file_id.total_file_data: number of file data bytes processed (sum)
•file_id.total_files: number of files processed (sum)
•file_log.total_events: total file events (sum)
•ftp_data.packets: total packets (sum)
•ftp_server.concurrent_sessions: total concurrent FTP sessions (now)
•ftp_server.max_concurrent_sessions: maximum concurrent FTP sessions (max)
•ftp_server.total_packets: total packets (sum)
•gtp_inspect.concurrent_sessions: total concurrent gtp sessions (now)
•gtp_inspect.events: requests (sum)
•gtp_inspect.max_concurrent_sessions: maximum concurrent gtp sessions (max)
•gtp_inspect.sessions: total sessions processed (sum)
•gtp_inspect.unknown_infos: unknown information elements (sum)
•gtp_inspect.unknown_types: unknown message types (sum)
•high_availability.packets: total packets (sum)
•host_cache.lru_cache_adds: lru cache added new entry (sum)
•host_cache.lru_cache_clears: lru cache clear API calls (sum)
•host_cache.lru_cache_find_hits: lru cache found entry in cache (sum)
•host_cache.lru_cache_find_misses: lru cache did not find entry in cache (sum)
•host_cache.lru_cache_prunes: lru cache pruned entry to make space for new entry (sum)
•host_cache.lru_cache_removes: lru cache found entry and removed it (sum)
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•host_cache.lru_cache_replaces: lru cache replaced existing entry (sum)
•host_tracker.service_adds: host service adds (sum)
•host_tracker.service_finds: host service finds (sum)
•host_tracker.service_removes: host service removes (sum)
•http_inspect.chunked: chunked message bodies (sum)
•http_inspect.concurrent_sessions: total concurrent http sessions (now)
•http_inspect.connect_requests: CONNECT requests inspected (sum)
•http_inspect.delete_requests: DELETE requests inspected (sum)
•http_inspect.flows: HTTP connections inspected (sum)
•http_inspect.get_requests: GET requests inspected (sum)
•http_inspect.head_requests: HEAD requests inspected (sum)
•http_inspect.inspections: total message sections inspected (sum)
•http_inspect.max_concurrent_sessions: maximum concurrent http sessions (max)
•http_inspect.options_requests: OPTIONS requests inspected (sum)
•http_inspect.other_requests: other request methods inspected (sum)
•http_inspect.post_requests: POST requests inspected (sum)
•http_inspect.put_requests: PUT requests inspected (sum)
•http_inspect.reassembles: TCP segments combined into HTTP messages (sum)
•http_inspect.request_bodies: POST, PUT, and other requests with message bodies (sum)
•http_inspect.requests: HTTP request messages inspected (sum)
•http_inspect.responses: HTTP response messages inspected (sum)
•http_inspect.scans: TCP segments scanned looking for HTTP messages (sum)
•http_inspect.trace_requests: TRACE requests inspected (sum)
•http_inspect.uri_coding: URIs with character coding problems (sum)
•http_inspect.uri_normalizations: URIs needing to be normalization (sum)
•http_inspect.uri_path: URIs with path problems (sum)
•icmp4.bad_checksum: non-zero icmp checksums (sum)
•icmp6.bad_icmp6_checksum: nonzero icmp6 checksums (sum)
•imap.b64_attachments: total base64 attachments decoded (sum)
•imap.b64_decoded_bytes: total base64 decoded bytes (sum)
•imap.concurrent_sessions: total concurrent imap sessions (now)
•imap.max_concurrent_sessions: maximum concurrent imap sessions (max)
•imap.non_encoded_attachments: total non-encoded attachments extracted (sum)
•imap.non_encoded_bytes: total non-encoded extracted bytes (sum)
•imap.packets: total packets processed (sum)
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•imap.qp_attachments: total quoted-printable attachments decoded (sum)
•imap.qp_decoded_bytes: total quoted-printable decoded bytes (sum)
•imap.sessions: total imap sessions (sum)
•imap.uu_attachments: total uu attachments decoded (sum)
•imap.uu_decoded_bytes: total uu decoded bytes (sum)
•ips.invalid_policy_ids: Number of times an invalid policy ID was provided (sum)
•ipv4.bad_checksum: nonzero ip checksums (sum)
•latency.max_usecs: maximum usecs elapsed (sum)
•latency.packet_timeouts: packets that timed out (sum)
•latency.rule_eval_timeouts: rule evals that timed out (sum)
•latency.rule_tree_enables: rule tree re-enables (sum)
•latency.total_packets: total packets monitored (sum)
•latency.total_rule_evals: total rule evals monitored (sum)
•latency.total_usecs: total usecs elapsed (sum)
•modbus.concurrent_sessions: total concurrent modbus sessions (now)
•modbus.frames: total Modbus messages (sum)
•modbus.max_concurrent_sessions: maximum concurrent modbus sessions (max)
•modbus.sessions: total sessions processed (sum)
•mpls.total_bytes: total mpls labeled bytes processed (sum)
•mpls.total_packets: total mpls labeled packets processed (sum)
•normalizer.icmp4_echo: icmp4 ping normalizations (sum)
•normalizer.icmp6_echo: icmp6 echo normalizations (sum)
•normalizer.ip4_df: don’t frag bit normalizations (sum)
•normalizer.ip4_opts: ip4 options cleared (sum)
•normalizer.ip4_rf: reserved flag bit clears (sum)
•normalizer.ip4_tos: type of service normalizations (sum)
•normalizer.ip4_trim: eth packets trimmed to datagram size (sum)
•normalizer.ip4_ttl: time-to-live normalizations (sum)
•normalizer.ip6_hops: ip6 hop limit normalizations (sum)
•normalizer.ip6_options: ip6 options cleared (sum)
•normalizer.tcp_block: blocked segments (sum)
•normalizer.tcp_ecn_pkt: packets with ECN bits cleared (sum)
•normalizer.tcp_ecn_session: ECN bits cleared (sum)
•normalizer.tcp_ips_data: normalized segments (sum)
•normalizer.tcp_nonce: packets with nonce bit cleared (sum)
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•normalizer.tcp_options: packets with options cleared (sum)
•normalizer.tcp_padding: packets with padding cleared (sum)
•normalizer.tcp_req_pay: cleared urgent pointer and urgent flag when there is no payload (sum)
•normalizer.tcp_req_urg: cleared urgent pointer when urgent flag is not set (sum)
•normalizer.tcp_req_urp: cleared the urgent flag if the urgent pointer is not set (sum)
•normalizer.tcp_reserved: packets with reserved bits cleared (sum)
•normalizer.tcp_syn_options: SYN only options cleared from non-SYN packets (sum)
•normalizer.tcp_trim_mss: data trimmed to MSS (sum)
•normalizer.tcp_trim_rst: RST packets with data trimmed (sum)
•normalizer.tcp_trim_syn: tcp segments trimmed on SYN (sum)
•normalizer.tcp_trim_win: data trimmed to window (sum)
•normalizer.tcp_ts_ecr: timestamp cleared on non-ACKs (sum)
•normalizer.tcp_ts_nop: timestamp options cleared (sum)
•normalizer.tcp_urgent_ptr: packets without data with urgent pointer cleared (sum)
•normalizer.test_icmp4_echo: test icmp4 ping normalizations (sum)
•normalizer.test_icmp6_echo: test icmp6 echo normalizations (sum)
•normalizer.test_ip4_df: test don’t frag bit normalizations (sum)
•normalizer.test_ip4_opts: test ip4 options cleared (sum)
•normalizer.test_ip4_rf: test reserved flag bit clears (sum)
•normalizer.test_ip4_tos: test type of service normalizations (sum)
•normalizer.test_ip4_trim: test eth packets trimmed to datagram size (sum)
•normalizer.test_ip4_ttl: test time-to-live normalizations (sum)
•normalizer.test_ip6_hops: test ip6 hop limit normalizations (sum)
•normalizer.test_ip6_options: test ip6 options cleared (sum)
•normalizer.test_tcp_block: test blocked segments (sum)
•normalizer.test_tcp_ecn_pkt: test packets with ECN bits cleared (sum)
•normalizer.test_tcp_ecn_session: test ECN bits cleared (sum)
•normalizer.test_tcp_ips_data: test normalized segments (sum)
•normalizer.test_tcp_nonce: test packets with nonce bit cleared (sum)
•normalizer.test_tcp_options: test packets with options cleared (sum)
•normalizer.test_tcp_padding: test packets with padding cleared (sum)
•normalizer.test_tcp_req_pay: test cleared urgent pointer and urgent flag when there is no payload (sum)
•normalizer.test_tcp_req_urg: test cleared urgent pointer when urgent flag is not set (sum)
•normalizer.test_tcp_req_urp: test cleared the urgent flag if the urgent pointer is not set (sum)
•normalizer.test_tcp_reserved: test packets with reserved bits cleared (sum)
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•normalizer.test_tcp_syn_options: test SYN only options cleared from non-SYN packets (sum)
•normalizer.test_tcp_trim_mss: test data trimmed to MSS (sum)
•normalizer.test_tcp_trim_rst: test RST packets with data trimmed (sum)
•normalizer.test_tcp_trim_syn: test tcp segments trimmed on SYN (sum)
•normalizer.test_tcp_trim_win: test data trimmed to window (sum)
•normalizer.test_tcp_ts_ecr: test timestamp cleared on non-ACKs (sum)
•normalizer.test_tcp_ts_nop: test timestamp options cleared (sum)
•normalizer.test_tcp_urgent_ptr: test packets without data with urgent pointer cleared (sum)
•packet_capture.captured: packets matching dumped after matching filter (sum)
•packet_capture.processed: packets processed against filter (sum)
•perf_monitor.packets: total packets (sum)
•pop.b64_attachments: total base64 attachments decoded (sum)
•pop.b64_decoded_bytes: total base64 decoded bytes (sum)
•pop.concurrent_sessions: total concurrent pop sessions (now)
•pop.max_concurrent_sessions: maximum concurrent pop sessions (max)
•pop.non_encoded_attachments: total non-encoded attachments extracted (sum)
•pop.non_encoded_bytes: total non-encoded extracted bytes (sum)
•pop.packets: total packets processed (sum)
•pop.qp_attachments: total quoted-printable attachments decoded (sum)
•pop.qp_decoded_bytes: total quoted-printable decoded bytes (sum)
•pop.sessions: total pop sessions (sum)
•pop.uu_attachments: total uu attachments decoded (sum)
•pop.uu_decoded_bytes: total uu decoded bytes (sum)
•port_scan.packets: total packets (sum)
•reg_test.packets: total packets (sum)
•reg_test.retry_packets: total retried packets received (sum)
•reg_test.retry_requests: total retry packets requested (sum)
•reputation.blacklisted: number of packets blacklisted (sum)
•reputation.memory_allocated: total memory allocated (sum)
•reputation.monitored: number of packets monitored (sum)
•reputation.packets: total packets processed (sum)
•reputation.whitelisted: number of packets whitelisted (sum)
•rpc_decode.concurrent_sessions: total concurrent rpc sessions (now)
•rpc_decode.max_concurrent_sessions: maximum concurrent rpc sessions (max)
•rpc_decode.total_packets: total packets (sum)
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•sd_pattern.below_threshold: sd_pattern matched but missed threshold (sum)
•sd_pattern.pattern_not_found: sd_pattern did not not match (sum)
•sd_pattern.terminated: hyperscan terminated (sum)
•search_engine.max_queued: maximum fast pattern matches queued for further evaluation (sum)
•search_engine.non_qualified_events: total non-qualified events (sum)
•search_engine.qualified_events: total qualified events (sum)
•search_engine.searched_bytes: total bytes searched (sum)
•search_engine.total_flushed: fast pattern matches discarded due to overflow (sum)
•search_engine.total_inserts: total fast pattern hits (sum)
•search_engine.total_unique: total unique fast pattern hits (sum)
•side_channel.packets: total packets (sum)
•sip.ack: ack (sum)
•sip.bye: bye (sum)
•sip.cancel: cancel (sum)
•sip.code_1xx: 1xx (sum)
•sip.code_2xx: 2xx (sum)
•sip.code_3xx: 3xx (sum)
•sip.code_4xx: 4xx (sum)
•sip.code_5xx: 5xx (sum)
•sip.code_6xx: 6xx (sum)
•sip.code_7xx: 7xx (sum)
•sip.code_8xx: 8xx (sum)
•sip.code_9xx: 9xx (sum)
•sip.concurrent_sessions: total concurrent SIP sessions (now)
•sip.dialogs: total dialogs (sum)
•sip.events: events generated (sum)
•sip.ignored_channels: total channels ignored (sum)
•sip.ignored_sessions: total sessions ignored (sum)
•sip.info: info (sum)
•sip.invite: invite (sum)
•sip.join: join (sum)
•sip.max_concurrent_sessions: maximum concurrent SIP sessions (max)
•sip.message: message (sum)
•sip.notify: notify (sum)
•sip.options: options (sum)
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•sip.packets: total packets (sum)
•sip.prack: prack (sum)
•sip.refer: refer (sum)
•sip.register: register (sum)
•sip.sessions: total sessions (sum)
•sip.subscribe: subscribe (sum)
•sip.total_requests: total requests (sum)
•sip.total_responses: total responses (sum)
•sip.update: update (sum)
•smtp.b64_attachments: total base64 attachments decoded (sum)
•smtp.b64_decoded_bytes: total base64 decoded bytes (sum)
•smtp.concurrent_sessions: total concurrent smtp sessions (now)
•smtp.max_concurrent_sessions: maximum concurrent smtp sessions (max)
•smtp.non_encoded_attachments: total non-encoded attachments extracted (sum)
•smtp.non_encoded_bytes: total non-encoded extracted bytes (sum)
•smtp.packets: total packets processed (sum)
•smtp.qp_attachments: total quoted-printable attachments decoded (sum)
•smtp.qp_decoded_bytes: total quoted-printable decoded bytes (sum)
•smtp.sessions: total smtp sessions (sum)
•smtp.uu_attachments: total uu attachments decoded (sum)
•smtp.uu_decoded_bytes: total uu decoded bytes (sum)
•snort.attribute_table_hosts: total number of hosts in table (sum)
•snort.attribute_table_reloads: number of times hosts table was reloaded (sum)
•snort.conf_reloads: number of times configuration was reloaded (sum)
•snort.daq_reloads: number of times daq configuration was reloaded (sum)
•snort.inspector_deletions: number of times inspectors were deleted (sum)
•snort.local_commands: total local commands processed (sum)
•snort.policy_reloads: number of times policies were reloaded (sum)
•snort.remote_commands: total remote commands processed (sum)
•snort.signals: total signals processed (sum)
•ssh.concurrent_sessions: total concurrent ssh sessions (now)
•ssh.max_concurrent_sessions: maximum concurrent ssh sessions (max)
•ssh.packets: total packets (sum)
•ssl.alert: total ssl alert records (sum)
•ssl.bad_handshakes: total bad handshakes (sum)
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•ssl.certificate: total ssl certificates (sum)
•ssl.change_cipher: total change cipher records (sum)
•ssl.client_application: total client application records (sum)
•ssl.client_hello: total client hellos (sum)
•ssl.client_key_exchange: total client key exchanges (sum)
•ssl.concurrent_sessions: total concurrent ssl sessions (now)
•ssl.decoded: ssl packets decoded (sum)
•ssl.detection_disabled: total detection disabled (sum)
•ssl.finished: total handshakes finished (sum)
•ssl.handshakes_completed: total completed ssl handshakes (sum)
•ssl.max_concurrent_sessions: maximum concurrent ssl sessions (max)
•ssl.packets: total packets processed (sum)
•ssl.server_application: total server application records (sum)
•ssl.server_done: total server done (sum)
•ssl.server_hello: total server hellos (sum)
•ssl.server_key_exchange: total server key exchanges (sum)
•ssl.sessions_ignored: total sessions ignore (sum)
•ssl.unrecognized_records: total unrecognized records (sum)
•stream.file_excess_prunes: file sessions pruned due to excess (sum)
•stream.file_flows: total file sessions (sum)
•stream.file_ha_prunes: file sessions pruned by high availability sync (sum)
•stream.file_idle_prunes: file sessions pruned due to timeout (sum)
•stream.file_memcap_prunes: file sessions pruned due to memcap (sum)
•stream.file_preemptive_prunes: file sessions pruned during preemptive pruning (sum)
•stream.file_total_prunes: total file sessions pruned (sum)
•stream.file_uni_prunes: file uni sessions pruned (sum)
•stream_icmp.created: icmp session trackers created (sum)
•stream.icmp_excess_prunes: icmp sessions pruned due to excess (sum)
•stream.icmp_flows: total icmp sessions (sum)
•stream.icmp_ha_prunes: icmp sessions pruned by high availability sync (sum)
•stream.icmp_idle_prunes: icmp sessions pruned due to timeout (sum)
•stream_icmp.max: max icmp sessions (max)
•stream.icmp_memcap_prunes: icmp sessions pruned due to memcap (sum)
•stream.icmp_preemptive_prunes: icmp sessions pruned during preemptive pruning (sum)
•stream_icmp.prunes: icmp session prunes (sum)
Snort 3 User Manual 238 / 284
•stream_icmp.released: icmp session trackers released (sum)
•stream_icmp.sessions: total icmp sessions (sum)
•stream_icmp.timeouts: icmp session timeouts (sum)
•stream.icmp_total_prunes: total icmp sessions pruned (sum)
•stream.icmp_uni_prunes: icmp uni sessions pruned (sum)
•stream_ip.alerts: alerts generated (sum)
•stream_ip.anomalies: anomalies detected (sum)
•stream_ip.created: ip session trackers created (sum)
•stream_ip.current_frags: current fragments (now)
•stream_ip.discards: fragments discarded (sum)
•stream_ip.drops: fragments dropped (sum)
•stream.ip_excess_prunes: ip sessions pruned due to excess (sum)
•stream.ip_flows: total ip sessions (sum)
•stream_ip.fragmented_bytes: total fragmented bytes (sum)
•stream_ip.frag_timeouts: datagrams abandoned (sum)
•stream.ip_ha_prunes: ip sessions pruned by high availability sync (sum)
•stream.ip_idle_prunes: ip sessions pruned due to timeout (sum)
•stream_ip.max_frags: max fragments (sum)
•stream_ip.max: max ip sessions (max)
•stream.ip_memcap_prunes: ip sessions pruned due to memcap (sum)
•stream_ip.memory_used: current memory usage in bytes (now)
•stream_ip.nodes_deleted: fragments deleted from tracker (sum)
•stream_ip.nodes_inserted: fragments added to tracker (sum)
•stream_ip.overlaps: overlapping fragments (sum)
•stream.ip_preemptive_prunes: ip sessions pruned during preemptive pruning (sum)
•stream_ip.prunes: ip session prunes (sum)
•stream_ip.reassembled_bytes: total reassembled bytes (sum)
•stream_ip.reassembled: reassembled datagrams (sum)
•stream_ip.released: ip session trackers released (sum)
•stream_ip.sessions: total ip sessions (sum)
•stream_ip.timeouts: ip session timeouts (sum)
•stream_ip.total_frags: total fragments (sum)
•stream.ip_total_prunes: total ip sessions pruned (sum)
•stream_ip.trackers_added: datagram trackers created (sum)
•stream_ip.trackers_cleared: datagram trackers cleared (sum)
Snort 3 User Manual 239 / 284
•stream_ip.trackers_completed: datagram trackers completed (sum)
•stream_ip.trackers_freed: datagram trackers released (sum)
•stream.ip_uni_prunes: ip uni sessions pruned (sum)
•stream_tcp.client_cleanups: number of times data from server was flushed when session released (sum)
•stream_tcp.closing: number of sessions currently closing (now)
•stream_tcp.created: tcp session trackers created (sum)
•stream_tcp.data_trackers: tcp session tracking started on data (sum)
•stream_tcp.discards: tcp packets discarded (sum)
•stream_tcp.established: number of sessions currently established (now)
•stream_tcp.events: events generated (sum)
•stream_tcp.exceeded_max_bytes: number of times the maximum queued byte limit was reached (sum)
•stream_tcp.exceeded_max_segs: number of times the maximum queued segment limit was reached (sum)
•stream.tcp_excess_prunes: tcp sessions pruned due to excess (sum)
•stream_tcp.fins: number of fin packets (sum)
•stream.tcp_flows: total tcp sessions (sum)
•stream_tcp.gaps: missing data between PDUs (sum)
•stream.tcp_ha_prunes: tcp sessions pruned by high availability sync (sum)
•stream.tcp_idle_prunes: tcp sessions pruned due to timeout (sum)
•stream_tcp.ignored: tcp packets ignored (sum)
•stream_tcp.initializing: number of sessions currently initializing (now)
•stream_tcp.internal_events: 135:X events generated (sum)
•stream_tcp.max: max tcp sessions (max)
•stream.tcp_memcap_prunes: tcp sessions pruned due to memcap (sum)
•stream_tcp.memory: current memory in use (now)
•stream_tcp.overlaps: overlapping segments queued (sum)
•stream.tcp_preemptive_prunes: tcp sessions pruned during preemptive pruning (sum)
•stream_tcp.prunes: tcp session prunes (sum)
•stream_tcp.rebuilt_buffers: rebuilt PDU sections (sum)
•stream_tcp.rebuilt_bytes: total rebuilt bytes (sum)
•stream_tcp.rebuilt_packets: total reassembled PDUs (sum)
•stream_tcp.released: tcp session trackers released (sum)
•stream_tcp.resets: number of reset packets (sum)
•stream_tcp.resyns: SYN received on established session (sum)
•stream_tcp.segs_queued: total segments queued (sum)
•stream_tcp.segs_released: total segments released (sum)
Snort 3 User Manual 240 / 284
•stream_tcp.segs_split: tcp segments split when reassembling PDUs (sum)
•stream_tcp.segs_used: queued tcp segments applied to reassembled PDUs (sum)
•stream_tcp.server_cleanups: number of times data from client was flushed when session released (sum)
•stream_tcp.sessions: total tcp sessions (sum)
•stream_tcp.syn_acks: number of syn-ack packets (sum)
•stream_tcp.syn_ack_trackers: tcp session tracking started on syn-ack (sum)
•stream_tcp.syns: number of syn packets (sum)
•stream_tcp.syn_trackers: tcp session tracking started on syn (sum)
•stream_tcp.three_way_trackers: tcp session tracking started on ack (sum)
•stream_tcp.timeouts: tcp session timeouts (sum)
•stream.tcp_total_prunes: total tcp sessions pruned (sum)
•stream.tcp_uni_prunes: tcp uni sessions pruned (sum)
•stream_tcp.untracked: tcp packets not tracked (sum)
•stream_udp.created: udp session trackers created (sum)
•stream.udp_excess_prunes: udp sessions pruned due to excess (sum)
•stream.udp_flows: total udp sessions (sum)
•stream.udp_ha_prunes: udp sessions pruned by high availability sync (sum)
•stream.udp_idle_prunes: udp sessions pruned due to timeout (sum)
•stream_udp.ignored: udp packets ignored (sum)
•stream_udp.max: max udp sessions (max)
•stream.udp_memcap_prunes: udp sessions pruned due to memcap (sum)
•stream.udp_preemptive_prunes: udp sessions pruned during preemptive pruning (sum)
•stream_udp.prunes: udp session prunes (sum)
•stream_udp.released: udp session trackers released (sum)
•stream_udp.sessions: total udp sessions (sum)
•stream_udp.timeouts: udp session timeouts (sum)
•stream.udp_total_prunes: total udp sessions pruned (sum)
•stream.udp_uni_prunes: udp uni sessions pruned (sum)
•stream.user_excess_prunes: user sessions pruned due to excess (sum)
•stream.user_flows: total user sessions (sum)
•stream.user_ha_prunes: user sessions pruned by high availability sync (sum)
•stream.user_idle_prunes: user sessions pruned due to timeout (sum)
•stream.user_memcap_prunes: user sessions pruned due to memcap (sum)
•stream.user_preemptive_prunes: user sessions pruned during preemptive pruning (sum)
•stream.user_total_prunes: total user sessions pruned (sum)
Snort 3 User Manual 241 / 284
•stream.user_uni_prunes: user uni sessions pruned (sum)
•tcp.bad_tcp4_checksum: nonzero tcp over ip checksums (sum)
•tcp.bad_tcp6_checksum: nonzero tcp over ipv6 checksums (sum)
•tcp_connector.messages: total messages (sum)
•telnet.concurrent_sessions: total concurrent Telnet sessions (now)
•telnet.max_concurrent_sessions: maximum concurrent Telnet sessions (max)
•telnet.total_packets: total packets (sum)
•udp.bad_udp4_checksum: nonzero udp over ipv4 checksums (sum)
•udp.bad_udp6_checksum: nonzero udp over ipv6 checksums (sum)
•wizard.tcp_hits: tcp identifications (sum)
•wizard.tcp_scans: tcp payload scans (sum)
•wizard.udp_hits: udp identifications (sum)
•wizard.udp_scans: udp payload scans (sum)
•wizard.user_hits: user identifications (sum)
•wizard.user_scans: user payload scans (sum)
20.6 Generators
•105: back_orifice
•106: rpc_decode
•112: arp_spoof
•116: arp
•116: auth
•116: ciscometadata
•116: decode
•116: eapol
•116: erspan2
•116: erspan3
•116: esp
•116: eth
•116: fabricpath
•116: gre
•116: gtp
•116: icmp4
•116: icmp6
•116: igmp
Snort 3 User Manual 242 / 284
•116: ipv4
•116: ipv6
•116: llc
•116: mpls
•116: pbb
•116: pgm
•116: pppoe
•116: tcp
•116: token_ring
•116: udp
•116: vlan
•116: wlan
•119: http_inspect
•122: port_scan
•123: stream_ip
•124: smtp
•125: ftp_server
•126: telnet
•128: ssh
•129: stream_tcp
•131: dns
•133: dce_http_proxy
•133: dce_http_server
•133: dce_smb
•133: dce_tcp
•133: dce_udp
•134: latency
•136: reputation
•137: ssl
•140: sip
•141: imap
•142: pop
•143: gtp_inspect
•144: modbus
•145: dnp3
•256: dpx
Snort 3 User Manual 243 / 284
20.7 Builtin Rules
•105:1 (back_orifice) BO traffic detected
•105:2 (back_orifice) BO client traffic detected
•105:3 (back_orifice) BO server traffic detected
•105:4 (back_orifice) BO Snort buffer attack
•106:1 (rpc_decode) fragmented RPC records
•106:2 (rpc_decode) multiple RPC records
•106:3 (rpc_decode) large RPC record fragment
•106:4 (rpc_decode) incomplete RPC segment
•106:5 (rpc_decode) zero-length RPC fragment
•112:1 (arp_spoof) unicast ARP request
•112:2 (arp_spoof) ethernet/ARP mismatch request for source
•112:3 (arp_spoof) ethernet/ARP mismatch request for destination
•112:4 (arp_spoof) attempted ARP cache overwrite attack
•116:1 (ipv4) not IPv4 datagram
•116:2 (ipv4) IPv4 header length < minimum
•116:3 (ipv4) IPv4 datagram length < header field
•116:4 (ipv4) IPv4 options found with bad lengths
•116:5 (ipv4) truncated IPv4 options
•116:6 (ipv4) IPv4 datagram length > captured length
•116:45 (tcp) TCP packet length is smaller than 20 bytes
•116:46 (tcp) TCP data offset is less than 5
•116:47 (tcp) TCP header length exceeds packet length
•116:54 (tcp) TCP options found with bad lengths
•116:55 (tcp) truncated TCP options
•116:56 (tcp) T/TCP detected
•116:57 (tcp) obsolete TCP options found
•116:58 (tcp) experimental TCP options found
•116:59 (tcp) TCP window scale option found with length > 14
•116:95 (udp) truncated UDP header
•116:96 (udp) invalid UDP header, length field < 8
•116:97 (udp) short UDP packet, length field > payload length
•116:98 (udp) long UDP packet, length field < payload length
•116:105 (icmp4) ICMP header truncated
•116:106 (icmp4) ICMP timestamp header truncated
Snort 3 User Manual 244 / 284
•116:107 (icmp4) ICMP address header truncated
•116:109 (arp) truncated ARP
•116:110 (eapol) truncated EAP header
•116:111 (eapol) EAP key truncated
•116:112 (eapol) EAP header truncated
•116:120 (pppoe) bad PPPOE frame detected
•116:130 (vlan) bad VLAN frame
•116:131 (llc) bad LLC header
•116:132 (llc) bad extra LLC info
•116:133 (wlan) bad 802.11 LLC header
•116:134 (wlan) bad 802.11 extra LLC info
•116:140 (token_ring) bad Token Ring header
•116:141 (token_ring) bad Token Ring ETHLLC header
•116:142 (token_ring) bad Token Ring MRLEN header
•116:143 (token_ring) bad Token Ring MR header
•116:150 (decode) loopback IP
•116:151 (decode) same src/dst IP
•116:160 (gre) GRE header length > payload length
•116:161 (gre) multiple encapsulations in packet
•116:162 (gre) invalid GRE version
•116:163 (gre) invalid GRE header
•116:164 (gre) invalid GRE v.1 PPTP header
•116:165 (gre) GRE trans header length > payload length
•116:170 (mpls) bad MPLS frame
•116:171 (mpls) MPLS label 0 appears in non-bottom header
•116:172 (mpls) MPLS label 1 appears in bottom header
•116:173 (mpls) MPLS label 2 appears in non-bottom header
•116:174 (mpls) MPLS label 3 appears in header
•116:175 (mpls) MPLS label 4, 5,.. or 15 appears in header
•116:176 (mpls) too many MPLS headers
•116:250 (icmp4) ICMP original IP header truncated
•116:251 (icmp4) ICMP version and original IP header versions differ
•116:252 (icmp4) ICMP original datagram length < original IP header length
•116:253 (icmp4) ICMP original IP payload < 64 bits
•116:254 (icmp4) ICMP original IP payload > 576 bytes
Snort 3 User Manual 245 / 284
•116:255 (icmp4) ICMP original IP fragmented and offset not 0
•116:270 (ipv6) IPv6 packet below TTL limit
•116:271 (ipv6) IPv6 header claims to not be IPv6
•116:272 (ipv6) IPv6 truncated extension header
•116:273 (ipv6) IPv6 truncated header
•116:274 (ipv6) IPv6 datagram length < header field
•116:275 (ipv6) IPv6 datagram length > captured length
•116:276 (ipv6) IPv6 packet with destination address ::0
•116:277 (ipv6) IPv6 packet with multicast source address
•116:278 (ipv6) IPv6 packet with reserved multicast destination address
•116:279 (ipv6) IPv6 header includes an undefined option type
•116:280 (ipv6) IPv6 address includes an unassigned multicast scope value
•116:281 (ipv6) IPv6 header includes an invalid value for the next header field
•116:282 (ipv6) IPv6 header includes a routing extension header followed by a hop-by-hop header
•116:283 (ipv6) IPv6 header includes two routing extension headers
•116:285 (icmp6) ICMPv6 packet of type 2 (message too big) with MTU field < 1280
•116:286 (icmp6) ICMPv6 packet of type 1 (destination unreachable) with non-RFC 2463 code
•116:287 (icmp6) ICMPv6 router solicitation packet with a code not equal to 0
•116:288 (icmp6) ICMPv6 router advertisement packet with a code not equal to 0
•116:289 (icmp6) ICMPv6 router solicitation packet with the reserved field not equal to 0
•116:290 (icmp6) ICMPv6 router advertisement packet with the reachable time field set > 1 hour
•116:291 (ipv6) IPV6 tunneled over IPv4, IPv6 header truncated, possible Linux kernel attack
•116:292 (ipv6) IPv6 header has destination options followed by a routing header
•116:293 (decode) two or more IP (v4 and/or v6) encapsulation layers present
•116:294 (esp) truncated encapsulated security payload header
•116:295 (ipv6) IPv6 header includes an option which is too big for the containing header
•116:296 (ipv6) IPv6 packet includes out-of-order extension headers
•116:297 (gtp) two or more GTP encapsulation layers present
•116:298 (gtp) GTP header length is invalid
•116:400 (tcp) XMAS attack detected
•116:401 (tcp) Nmap XMAS attack detected
•116:402 (tcp) DOS NAPTHA vulnerability detected
•116:403 (tcp) SYN to multicast address
•116:404 (ipv4) IPv4 packet with zero TTL
•116:405 (ipv4) IPv4 packet with bad frag bits (both MF and DF set)
Snort 3 User Manual 246 / 284
•116:406 (udp) invalid IPv6 UDP packet, checksum zero
•116:407 (ipv4) IPv4 packet frag offset + length exceed maximum
•116:408 (ipv4) IPv4 packet from current net source address
•116:409 (ipv4) IPv4 packet to current net dest address
•116:410 (ipv4) IPv4 packet from multicast source address
•116:411 (ipv4) IPv4 packet from reserved source address
•116:412 (ipv4) IPv4 packet to reserved dest address
•116:413 (ipv4) IPv4 packet from broadcast source address
•116:414 (ipv4) IPv4 packet to broadcast dest address
•116:415 (icmp4) ICMP4 packet to multicast dest address
•116:416 (icmp4) ICMP4 packet to broadcast dest address
•116:418 (icmp4) ICMP4 type other
•116:419 (tcp) TCP urgent pointer exceeds payload length or no payload
•116:420 (tcp) TCP SYN with FIN
•116:421 (tcp) TCP SYN with RST
•116:422 (tcp) TCP PDU missing ack for established session
•116:423 (tcp) TCP has no SYN, ACK, or RST
•116:424 (eth) truncated ethernet header
•116:424 (pbb) truncated ethernet header
•116:425 (ipv4) truncated IPv4 header
•116:426 (icmp4) truncated ICMP4 header
•116:427 (icmp6) truncated ICMPv6 header
•116:428 (ipv4) IPv4 packet below TTL limit
•116:429 (ipv6) IPv6 packet has zero hop limit
•116:430 (ipv4) IPv4 packet both DF and offset set
•116:431 (icmp6) ICMPv6 type not decoded
•116:432 (icmp6) ICMPv6 packet to multicast address
•116:433 (tcp) DDOS shaft SYN flood
•116:434 (icmp4) ICMP ping Nmap
•116:435 (icmp4) ICMP icmpenum v1.1.1
•116:436 (icmp4) ICMP redirect host
•116:437 (icmp4) ICMP redirect net
•116:438 (icmp4) ICMP traceroute ipopts
•116:439 (icmp4) ICMP source quench
•116:440 (icmp4) broadscan smurf scanner
Snort 3 User Manual 247 / 284
•116:441 (icmp4) ICMP destination unreachable communication administratively prohibited
•116:442 (icmp4) ICMP destination unreachable communication with destination host is administratively prohibited
•116:443 (icmp4) ICMP destination unreachable communication with destination network is administratively prohibited
•116:444 (ipv4) IPv4 option set
•116:445 (udp) large UDP packet (> 4000 bytes)
•116:446 (tcp) TCP port 0 traffic
•116:447 (udp) UDP port 0 traffic
•116:448 (ipv4) IPv4 reserved bit set
•116:449 (decode) unassigned/reserved IP protocol
•116:450 (decode) bad IP protocol
•116:451 (icmp4) ICMP path MTU denial of service attempt
•116:452 (icmp4) Linux ICMP header DOS attempt
•116:453 (ipv6) ISATAP-addressed IPv6 traffic spoofing attempt
•116:454 (pgm) PGM nak list overflow attempt
•116:455 (igmp) DOS IGMP IP options validation attempt
•116:456 (ipv6) too many IPv6 extension headers
•116:457 (icmp6) ICMPv6 packet of type 1 (destination unreachable) with non-RFC 4443 code
•116:458 (ipv6) bogus fragmentation packet, possible BSD attack
•116:459 (decode) fragment with zero length
•116:460 (icmp6) ICMPv6 node info query/response packet with a code greater than 2
•116:461 (ipv6) IPv6 routing type 0 extension header
•116:462 (erspan2) ERSpan header version mismatch
•116:463 (erspan2) captured length < ERSpan type2 header length
•116:464 (erspan3) captured < ERSpan type3 header length
•116:465 (auth) truncated authentication header
•116:466 (auth) bad authentication header length
•116:467 (fabricpath) truncated FabricPath header
•116:468 (ciscometadata) truncated Cisco Metadata header
•116:469 (ciscometadata) invalid Cisco Metadata option length
•116:470 (ciscometadata) invalid Cisco Metadata option type
•116:471 (ciscometadata) invalid Cisco Metadata SGT
•116:472 (decode) too many protocols present
•116:473 (decode) ether type out of range
•116:474 (icmp6) ICMPv6 not encapsulated in IPv6
•116:475 (ipv6) IPv6 mobility header includes an invalid value for the payload protocol field
Snort 3 User Manual 248 / 284
•119:1 (http_inspect) ascii encoding
•119:2 (http_inspect) double decoding attack
•119:3 (http_inspect) u encoding
•119:4 (http_inspect) bare byte unicode encoding
•119:5 (http_inspect) obsolete event—deleted
•119:6 (http_inspect) UTF-8 encoding
•119:7 (http_inspect) unicode map code point encoding in URI
•119:8 (http_inspect) multi_slash encoding
•119:9 (http_inspect) backslash used in URI path
•119:10 (http_inspect) self directory traversal
•119:11 (http_inspect) directory traversal
•119:12 (http_inspect) apache whitespace (tab)
•119:13 (http_inspect) HTTP header line terminated by LF without a CR
•119:14 (http_inspect) non-RFC defined char
•119:15 (http_inspect) oversize request-uri directory
•119:16 (http_inspect) oversize chunk encoding
•119:17 (http_inspect) unauthorized proxy use detected
•119:18 (http_inspect) webroot directory traversal
•119:19 (http_inspect) long header
•119:20 (http_inspect) max header fields
•119:21 (http_inspect) multiple content length
•119:22 (http_inspect) obsolete event—deleted
•119:23 (http_inspect) invalid IP in true-client-IP/XFF header
•119:24 (http_inspect) multiple host hdrs detected
•119:25 (http_inspect) hostname exceeds 255 characters
•119:26 (http_inspect) too much whitespace in header (not implemented yet)
•119:27 (http_inspect) client consecutive small chunk sizes
•119:28 (http_inspect) POST or PUT w/o content-length or chunks
•119:29 (http_inspect) multiple true ips in a session
•119:30 (http_inspect) both true-client-IP and XFF hdrs present
•119:31 (http_inspect) unknown method
•119:32 (http_inspect) simple request
•119:33 (http_inspect) unescaped space in HTTP URI
•119:34 (http_inspect) too many pipelined requests
•119:35 (http_inspect) anomalous http server on undefined HTTP port
Snort 3 User Manual 249 / 284
•119:36 (http_inspect) invalid status code in HTTP response
•119:37 (http_inspect) unused event number—should not appear
•119:38 (http_inspect) HTTP response has UTF charset that failed to normalize
•119:39 (http_inspect) HTTP response has UTF-7 charset
•119:40 (http_inspect) HTTP response gzip decompression failed
•119:41 (http_inspect) server consecutive small chunk sizes
•119:42 (http_inspect) unused event number—should not appear
•119:43 (http_inspect) javascript obfuscation levels exceeds 1
•119:44 (http_inspect) javascript whitespaces exceeds max allowed
•119:45 (http_inspect) multiple encodings within javascript obfuscated data
•119:46 (http_inspect) SWF file zlib decompression failure
•119:47 (http_inspect) SWF file LZMA decompression failure
•119:48 (http_inspect) PDF file deflate decompression failure
•119:49 (http_inspect) PDF file unsupported compression type
•119:50 (http_inspect) PDF file cascaded compression
•119:51 (http_inspect) PDF file parse failure
•119:52 (http_inspect) not HTTP traffic
•119:53 (http_inspect) chunk length has excessive leading zeros
•119:54 (http_inspect) white space before or between messages
•119:55 (http_inspect) request message without URI
•119:56 (http_inspect) control character in reason phrase
•119:57 (http_inspect) illegal extra whitespace in start line
•119:58 (http_inspect) corrupted HTTP version
•119:59 (http_inspect) unknown HTTP version
•119:60 (http_inspect) format error in HTTP header
•119:61 (http_inspect) chunk header options present
•119:62 (http_inspect) URI badly formatted
•119:63 (http_inspect) unrecognized type of percent encoding in URI
•119:64 (http_inspect) HTTP chunk misformatted
•119:65 (http_inspect) white space following chunk length
•119:66 (http_inspect) white space within header name
•119:67 (http_inspect) excessive gzip compression
•119:68 (http_inspect) gzip decompression failed
•119:69 (http_inspect) HTTP 0.9 requested followed by another request
•119:70 (http_inspect) HTTP 0.9 request following a normal request
Snort 3 User Manual 250 / 284
•119:71 (http_inspect) message has both Content-Length and Transfer-Encoding
•119:72 (http_inspect) status code implying no body combined with Transfer-Encoding or nonzero Content-Length
•119:73 (http_inspect) Transfer-Encoding not ending with chunked
•119:74 (http_inspect) Transfer-Encoding with encodings before chunked
•119:75 (http_inspect) misformatted HTTP traffic
•119:76 (http_inspect) unsupported Content-Encoding used
•119:77 (http_inspect) unknown Content-Encoding used
•119:78 (http_inspect) multiple Content-Encodings applied
•119:79 (http_inspect) server response before client request
•119:80 (http_inspect) PDF/SWF decompression of server response too big
•119:81 (http_inspect) nonprinting character in HTTP message header name
•119:82 (http_inspect) bad Content-Length value in HTTP header
•119:83 (http_inspect) HTTP header line wrapped
•119:84 (http_inspect) HTTP header line terminated by CR without a LF
•119:85 (http_inspect) chunk terminated by nonstandard separator
•119:86 (http_inspect) chunk length terminated by LF without CR
•119:87 (http_inspect) more than one response with 100 status code
•119:88 (http_inspect) 100 status code not in response to Expect header
•119:89 (http_inspect) 1XX status code other than 100 or 101
•119:90 (http_inspect) Expect header sent without a message body
•119:91 (http_inspect) HTTP 1.0 message with Transfer-Encoding header
•119:92 (http_inspect) Content-Transfer-Encoding used as HTTP header
•119:93 (http_inspect) illegal field in chunked message trailers
•119:94 (http_inspect) header field inappropriately appears twice or has two values
•119:95 (http_inspect) invalid value chunked in Content-Encoding header
•119:96 (http_inspect) 206 response sent to a request without a Range header
•119:97 (http_inspect) HTTP in version field not all upper case
•122:1 (port_scan) TCP portscan
•122:2 (port_scan) TCP decoy portscan
•122:3 (port_scan) TCP portsweep
•122:4 (port_scan) TCP distributed portscan
•122:5 (port_scan) TCP filtered portscan
•122:6 (port_scan) TCP filtered decoy portscan
•122:7 (port_scan) TCP filtered portsweep
•122:8 (port_scan) TCP filtered distributed portscan
Snort 3 User Manual 251 / 284
•122:9 (port_scan) IP protocol scan
•122:10 (port_scan) IP decoy protocol scan
•122:11 (port_scan) IP protocol sweep
•122:12 (port_scan) IP distributed protocol scan
•122:13 (port_scan) IP filtered protocol scan
•122:14 (port_scan) IP filtered decoy protocol scan
•122:15 (port_scan) IP filtered protocol sweep
•122:16 (port_scan) IP filtered distributed protocol scan
•122:17 (port_scan) UDP portscan
•122:18 (port_scan) UDP decoy portscan
•122:19 (port_scan) UDP portsweep
•122:20 (port_scan) UDP distributed portscan
•122:21 (port_scan) UDP filtered portscan
•122:22 (port_scan) UDP filtered decoy portscan
•122:23 (port_scan) UDP filtered portsweep
•122:24 (port_scan) UDP filtered distributed portscan
•122:25 (port_scan) ICMP sweep
•122:26 (port_scan) ICMP filtered sweep
•122:27 (port_scan) open port
•123:1 (stream_ip) inconsistent IP options on fragmented packets
•123:2 (stream_ip) teardrop attack
•123:3 (stream_ip) short fragment, possible DOS attempt
•123:4 (stream_ip) fragment packet ends after defragmented packet
•123:5 (stream_ip) zero-byte fragment packet
•123:6 (stream_ip) bad fragment size, packet size is negative
•123:7 (stream_ip) bad fragment size, packet size is greater than 65536
•123:8 (stream_ip) fragmentation overlap
•123:11 (stream_ip) TTL value less than configured minimum, not using for reassembly
•123:12 (stream_ip) excessive fragment overlap
•123:13 (stream_ip) tiny fragment
•124:1 (smtp) attempted command buffer overflow
•124:2 (smtp) attempted data header buffer overflow
•124:3 (smtp) attempted response buffer overflow
•124:4 (smtp) attempted specific command buffer overflow
•124:5 (smtp) unknown command
Snort 3 User Manual 252 / 284
•124:6 (smtp) illegal command
•124:7 (smtp) attempted header name buffer overflow
•124:8 (smtp) attempted X-Link2State command buffer overflow
•124:10 (smtp) base64 decoding failed
•124:11 (smtp) quoted-printable decoding failed
•124:13 (smtp) Unix-to-Unix decoding failed
•124:14 (smtp) Cyrus SASL authentication attack
•124:15 (smtp) attempted authentication command buffer overflow
•125:1 (ftp_server) TELNET cmd on FTP command channel
•125:2 (ftp_server) invalid FTP command
•125:3 (ftp_server) FTP command parameters were too long
•125:4 (ftp_server) FTP command parameters were malformed
•125:5 (ftp_server) FTP command parameters contained potential string format
•125:6 (ftp_server) FTP response message was too long
•125:7 (ftp_server) FTP traffic encrypted
•125:8 (ftp_server) FTP bounce attempt
•125:9 (ftp_server) evasive (incomplete) TELNET cmd on FTP command channel
•126:1 (telnet) consecutive Telnet AYT commands beyond threshold
•126:2 (telnet) Telnet traffic encrypted
•126:3 (telnet) Telnet subnegotiation begin command without subnegotiation end
•128:1 (ssh) challenge-response overflow exploit
•128:2 (ssh) SSH1 CRC32 exploit
•128:3 (ssh) server version string overflow
•128:5 (ssh) bad message direction
•128:6 (ssh) payload size incorrect for the given payload
•128:7 (ssh) failed to detect SSH version string
•129:1 (stream_tcp) SYN on established session
•129:2 (stream_tcp) data on SYN packet
•129:3 (stream_tcp) data sent on stream not accepting data
•129:4 (stream_tcp) TCP timestamp is outside of PAWS window
•129:5 (stream_tcp) bad segment, adjusted size ⇐0 (deprecated)
•129:6 (stream_tcp) window size (after scaling) larger than policy allows
•129:7 (stream_tcp) limit on number of overlapping TCP packets reached
•129:8 (stream_tcp) data sent on stream after TCP reset sent
•129:9 (stream_tcp) TCP client possibly hijacked, different ethernet address
Snort 3 User Manual 253 / 284
•129:10 (stream_tcp) TCP server possibly hijacked, different ethernet address
•129:11 (stream_tcp) TCP data with no TCP flags set
•129:12 (stream_tcp) consecutive TCP small segments exceeding threshold
•129:13 (stream_tcp) 4-way handshake detected
•129:14 (stream_tcp) TCP timestamp is missing
•129:15 (stream_tcp) reset outside window
•129:16 (stream_tcp) FIN number is greater than prior FIN
•129:17 (stream_tcp) ACK number is greater than prior FIN
•129:18 (stream_tcp) data sent on stream after TCP reset received
•129:19 (stream_tcp) TCP window closed before receiving data
•129:20 (stream_tcp) TCP session without 3-way handshake
•131:1 (dns) obsolete DNS RR types
•131:2 (dns) experimental DNS RR types
•131:3 (dns) DNS client rdata txt overflow
•133:2 (dce_smb) SMB - bad NetBIOS session service session type
•133:3 (dce_smb) SMB - bad SMB message type
•133:4 (dce_smb) SMB - bad SMB Id (not \xffSMB for SMB1 or not \xfeSMB for SMB2)
•133:5 (dce_smb) SMB - bad word count or structure size
•133:6 (dce_smb) SMB - bad byte count
•133:7 (dce_smb) SMB - bad format type
•133:8 (dce_smb) SMB - bad offset
•133:9 (dce_smb) SMB - zero total data count
•133:10 (dce_smb) SMB - NetBIOS data length less than SMB header length
•133:12 (dce_smb) SMB - remaining NetBIOS data length less than command byte count
•133:13 (dce_smb) SMB - remaining NetBIOS data length less than command data size
•133:14 (dce_smb) SMB - remaining total data count less than this command data size
•133:15 (dce_smb) SMB - total data sent (STDu64) greater than command total data expected
•133:16 (dce_smb) SMB - byte count less than command data size (STDu64)
•133:17 (dce_smb) SMB - invalid command data size for byte count
•133:18 (dce_smb) SMB - excessive tree connect requests with pending tree connect responses
•133:19 (dce_smb) SMB - excessive read requests with pending read responses
•133:20 (dce_smb) SMB - excessive command chaining
•133:21 (dce_smb) SMB - multiple chained tree connect requests
•133:22 (dce_smb) SMB - multiple chained tree connect requests
•133:23 (dce_smb) SMB - chained/compounded login followed by logoff
Snort 3 User Manual 254 / 284
•133:24 (dce_smb) SMB - chained/compounded tree connect followed by tree disconnect
•133:25 (dce_smb) SMB - chained/compounded open pipe followed by close pipe
•133:26 (dce_smb) SMB - invalid share access
•133:27 (dce_tcp) connection oriented DCE/RPC - invalid major version
•133:28 (dce_tcp) connection oriented DCE/RPC - invalid minor version
•133:29 (dce_tcp) connection-oriented DCE/RPC - invalid PDU type
•133:30 (dce_tcp) connection-oriented DCE/RPC - fragment length less than header size
•133:32 (dce_tcp) connection-oriented DCE/RPC - no context items specified
•133:33 (dce_tcp) connection-oriented DCE/RPC -no transfer syntaxes specified
•133:34 (dce_tcp) connection-oriented DCE/RPC - fragment length on non-last fragment less than maximum negotiated frag-
ment transmit size for client
•133:35 (dce_tcp) connection-oriented DCE/RPC - fragment length greater than maximum negotiated fragment transmit size
•133:36 (dce_tcp) connection-oriented DCE/RPC - alter context byte order different from bind
•133:37 (dce_tcp) connection-oriented DCE/RPC - call id of non first/last fragment different from call id established for frag-
mented request
•133:38 (dce_tcp) connection-oriented DCE/RPC - opnum of non first/last fragment different from opnum established for
fragmented request
•133:39 (dce_tcp) connection-oriented DCE/RPC - context id of non first/last fragment different from context id established for
fragmented request
•133:40 (dce_udp) connection-less DCE/RPC - invalid major version
•133:41 (dce_udp) connection-less DCE/RPC - invalid PDU type
•133:42 (dce_udp) connection-less DCE/RPC - data length less than header size
•133:43 (dce_udp) connection-less DCE/RPC - bad sequence number
•133:44 (dce_smb) SMB - invalid SMB version 1 seen
•133:45 (dce_smb) SMB - invalid SMB version 2 seen
•133:46 (dce_smb) SMB - invalid user, tree connect, file binding
•133:47 (dce_smb) SMB - excessive command compounding
•133:48 (dce_smb) SMB - zero data count
•133:50 (dce_smb) SMB - maximum number of outstanding requests exceeded
•133:51 (dce_smb) SMB - outstanding requests with same MID
•133:52 (dce_smb) SMB - deprecated dialect negotiated
•133:53 (dce_smb) SMB - deprecated command used
•133:54 (dce_smb) SMB - unusual command used
•133:55 (dce_smb) SMB - invalid setup count for command
•133:56 (dce_smb) SMB - client attempted multiple dialect negotiations on session
•133:57 (dce_smb) SMB - client attempted to create or set a file’s attributes to readonly/hidden/system
Snort 3 User Manual 255 / 284
•133:58 (dce_smb) SMB - file offset provided is greater than file size specified
•133:59 (dce_smb) SMB - next command specified in SMB2 header is beyond payload boundary
•134:1 (latency) rule tree suspended due to latency
•134:2 (latency) rule tree re-enabled after suspend timeout
•134:3 (latency) packet fastpathed due to latency
•136:1 (reputation) packets blacklisted
•136:2 (reputation) packets whitelisted
•136:3 (reputation) packets monitored
•137:1 (ssl) invalid client HELLO after server HELLO detected
•137:2 (ssl) invalid server HELLO without client HELLO detected
•137:3 (ssl) heartbeat read overrun attempt detected
•137:4 (ssl) large heartbeat response detected
•140:2 (sip) empty request URI
•140:3 (sip) URI is too long
•140:4 (sip) empty call-Id
•140:5 (sip) Call-Id is too long
•140:6 (sip) CSeq number is too large or negative
•140:7 (sip) request name in CSeq is too long
•140:8 (sip) empty From header
•140:9 (sip) From header is too long
•140:10 (sip) empty To header
•140:11 (sip) To header is too long
•140:12 (sip) empty Via header
•140:13 (sip) Via header is too long
•140:14 (sip) empty Contact
•140:15 (sip) contact is too long
•140:16 (sip) content length is too large or negative
•140:17 (sip) multiple SIP messages in a packet
•140:18 (sip) content length mismatch
•140:19 (sip) request name is invalid
•140:20 (sip) Invite replay attack
•140:21 (sip) illegal session information modification
•140:22 (sip) response status code is not a 3 digit number
•140:23 (sip) empty Content-type header
•140:24 (sip) SIP version is invalid
Snort 3 User Manual 256 / 284
•140:25 (sip) mismatch in METHOD of request and the CSEQ header
•140:26 (sip) method is unknown
•140:27 (sip) maximum dialogs within a session reached
•141:1 (imap) unknown IMAP3 command
•141:2 (imap) unknown IMAP3 response
•141:4 (imap) base64 decoding failed
•141:5 (imap) quoted-printable decoding failed
•141:7 (imap) Unix-to-Unix decoding failed
•142:1 (pop) unknown POP3 command
•142:2 (pop) unknown POP3 response
•142:4 (pop) base64 decoding failed
•142:5 (pop) quoted-printable decoding failed
•142:7 (pop) Unix-to-Unix decoding failed
•143:1 (gtp_inspect) message length is invalid
•143:2 (gtp_inspect) information element length is invalid
•143:3 (gtp_inspect) information elements are out of order
•144:1 (modbus) length in Modbus MBAP header does not match the length needed for the given function
•144:2 (modbus) Modbus protocol ID is non-zero
•144:3 (modbus) reserved Modbus function code in use
•145:1 (dnp3) DNP3 link-layer frame contains bad CRC
•145:2 (dnp3) DNP3 link-layer frame was dropped
•145:3 (dnp3) DNP3 transport-layer segment was dropped during reassembly
•145:4 (dnp3) DNP3 reassembly buffer was cleared without reassembling a complete message
•145:5 (dnp3) DNP3 link-layer frame uses a reserved address
•145:6 (dnp3) DNP3 application-layer fragment uses a reserved function code
•256:1 (dpx) too much data sent to port
20.8 Command Set
•packet_capture.disable(): stop packet dump
•packet_capture.enable(filter): dump raw packets
•snort.delete_inspector(inspector): delete an inspector from the default policy
•snort.detach(): exit shell w/o shutdown
•snort.dump_stats(): show summary statistics
•snort.help(): this output
•snort.pause(): suspend packet processing
Snort 3 User Manual 257 / 284
•snort.quit(): shutdown and dump-stats
•snort.reload_config(filename): load new configuration
•snort.reload_daq(): reload daq module
•snort.reload_hosts(filename): load a new hosts table
•snort.reload_policy(filename): reload part or all of the default policy
•snort.resume(): continue packet processing
•snort.rotate_stats(): roll perfmonitor log files
•snort.show_plugins(): show available plugins
20.9 Signals
Important
Signal numbers are for the system that generated this documentation and are not applicable elsewhere.
•hosts(23): reload hosts file
•int(2): shutdown normally
•quit(3): shutdown as if started with --dirty-pig
•reload(1): reload config file
•rotate(12): rotate stats files
•stats(10): dump stats to stdout
•term(15): shutdown normally
20.10 Configuration Changes
change -> dynamicdetection ==> ’snort.--plugin_path=<path>’
change -> dynamicengine ==> ’snort.--plugin_path=<path>’
change -> dynamicpreprocessor ==> ’snort.--plugin_path=<path>’
change -> dynamicsidechannel ==> ’snort.--plugin_path=<path>’
change -> alertfile: ’config alertfile:’ ==> ’alert_fast.file’
change -> alertfile: ’config alertfile:’ ==> ’alert_full.file’
change -> attribute_table: ’STREAM_POLICY’ ==> ’hosts: tcp_policy’
change -> attribute_table: ’filename <file_name>’ ==> ’hosts[]’
change -> config ’ addressspace_agnostic’ ==> ’ packets. address_space_agnostic’
change -> config ’ checksum_mode’ ==> ’ network. checksum_eval’
change -> config ’ daq’ ==> ’ daq. type’
change -> config ’ daq_dir’ ==> ’ daq. dir’
change -> config ’ daq_mode’ ==> ’ daq. mode’
change -> config ’ daq_var’ ==> ’ daq. var’
change -> config ’ detection_filter’ ==> ’ alerts. detection_filter_memcap’
change -> config ’ enable_deep_teredo_inspection’ ==> ’ udp. deep_teredo_inspection’
change -> config ’ event_filter’ ==> ’ alerts. event_filter_memcap’
change -> config ’ max_attribute_hosts’ ==> ’ attribute_table. max_hosts’
change -> config ’ max_attribute_services_per_host’ ==> ’ attribute_table. ←-
max_services_per_host’
change -> config ’ nopcre’ ==> ’ detection. pcre_enable’
Snort 3 User Manual 258 / 284
change -> config ’ pkt_count’ ==> ’ packets. limit’
change -> config ’ rate_filter’ ==> ’ alerts. rate_filter_memcap’
change -> config ’ react’ ==> ’ react. page’
change -> config ’ threshold’ ==> ’ alerts. event_filter_memcap’
change -> csv: ’dgmlen’ ==> ’dgm_len’
change -> csv: ’dst’ ==> ’dst_addr’
change -> csv: ’dstport’ ==> ’dst_port’
change -> csv: ’ethdst’ ==> ’eth_dst’
change -> csv: ’ethlen’ ==> ’eth_len’
change -> csv: ’ethsrc’ ==> ’eth_src’
change -> csv: ’ethtype’ ==> ’eth_type’
change -> csv: ’icmpcode’ ==> ’icmp_code’
change -> csv: ’icmpid’ ==> ’icmp_id’
change -> csv: ’icmpseq’ ==> ’icmp_seq’
change -> csv: ’icmptype’ ==> ’icmp_type’
change -> csv: ’iplen’ ==> ’ip_len’
change -> csv: ’sig_generator’ ==> ’gid’
change -> csv: ’sig_id’ ==> ’sid’
change -> csv: ’sig_rev’ ==> ’rev’
change -> csv: ’src’ ==> ’src_addr’
change -> csv: ’srcport’ ==> ’src_port’
change -> csv: ’tcpack’ ==> ’tcp_ack’
change -> csv: ’tcpflags’ ==> ’tcp_flags’
change -> csv: ’tcplen’ ==> ’tcp_len’
change -> csv: ’tcpseq’ ==> ’tcp_seq’
change -> csv: ’tcpwindow’ ==> ’tcp_win’
change -> csv: ’udplength’ ==> ’udp_len’
change -> detection: ’ac’ ==> ’ac_full_q’
change -> detection: ’ac-banded’ ==> ’ac_banded’
change -> detection: ’ac-bnfa’ ==> ’ac_bnfa_q’
change -> detection: ’ac-bnfa-nq’ ==> ’ac_bnfa’
change -> detection: ’ac-bnfa-q’ ==> ’ac_bnfa_q’
change -> detection: ’ac-nq’ ==> ’ac_full’
change -> detection: ’ac-q’ ==> ’ac_full_q’
change -> detection: ’ac-sparsebands’ ==> ’ac_sparse_bands’
change -> detection: ’ac-split’ ==> ’ac_full_q’
change -> detection: ’ac-split’ ==> ’split_any_any’
change -> detection: ’ac-std’ ==> ’ac_std’
change -> detection: ’acs’ ==> ’ac_sparse’
change -> detection: ’bleedover-port-limit’ ==> ’bleedover_port_limit’
change -> detection: ’intel-cpm’ ==> ’intel_cpm’
change -> detection: ’lowmem’ ==> ’lowmem_q’
change -> detection: ’lowmem-nq’ ==> ’lowmem’
change -> detection: ’lowmem-q’ ==> ’lowmem_q’
change -> detection: ’max-pattern-len’ ==> ’max_pattern_len’
change -> detection: ’search-method’ ==> ’search_method’
change -> detection: ’search-optimize’ ==> ’search_optimize’
change -> detection: ’split-any-any’ ==> ’split_any_any’
change -> dns: ’ports’ ==> ’bindings’
change -> event_filter: ’gen_id’ ==> ’gid’
change -> event_filter: ’sig_id’ ==> ’sid’
change -> event_filter: ’threshold’ ==> ’event_filter’
change -> file: ’config file: file_block_timeout’ ==> ’block_timeout’
change -> file: ’config file: file_type_depth’ ==> ’type_depth’
change -> file: ’config file: signature’ ==> ’enable_signature’
change -> file: ’config file: type_id’ ==> ’enable_type’
change -> frag3_engine: ’min_fragment_length’ ==> ’min_frag_length’
change -> frag3_engine: ’overlap_limit’ ==> ’max_overlaps’
change -> frag3_engine: ’policy bsd-right’ ==> ’policy = bsd_right’
change -> frag3_engine: ’timeout’ ==> ’session_timeout’
change -> ftp_telnet_protocol: ’alt_max_param_len’ ==> ’cmd_validity’
change -> ftp_telnet_protocol: ’data_chan’ ==> ’ignore_data_chan’
Snort 3 User Manual 259 / 284
change -> ftp_telnet_protocol: ’ports’ ==> ’bindings’
change -> gtp: ’ports’ ==> ’gtp_ports’
change -> http_inspect: ’http_inspect’ ==> ’http_global’
change -> http_inspect_server: ’apache_whitespace’ ==> ’profile.apache_whitespace’
change -> http_inspect_server: ’ascii’ ==> ’profile.ascii’
change -> http_inspect_server: ’bare_byte’ ==> ’profile.bare_byte’
change -> http_inspect_server: ’chunk_length’ ==> ’profile.chunk_length’
change -> http_inspect_server: ’client_flow_depth’ ==> ’profile.client_flow_depth’
change -> http_inspect_server: ’directory’ ==> ’profile.directory’
change -> http_inspect_server: ’double_decode’ ==> ’profile.double_decode’
change -> http_inspect_server: ’enable_cookie’ ==> ’enable_cookies’
change -> http_inspect_server: ’flow_depth’ ==> ’server_flow_depth’
change -> http_inspect_server: ’http_inspect_server’ ==> ’http_inspect’
change -> http_inspect_server: ’iis_backslash’ ==> ’profile.iis_backslash’
change -> http_inspect_server: ’iis_delimiter’ ==> ’profile.iis_delimiter’
change -> http_inspect_server: ’iis_unicode’ ==> ’profile.iis_unicode’
change -> http_inspect_server: ’max_header_length’ ==> ’profile.max_header_length’
change -> http_inspect_server: ’max_headers’ ==> ’profile.max_headers’
change -> http_inspect_server: ’max_spaces’ ==> ’profile.max_spaces’
change -> http_inspect_server: ’multi_slash’ ==> ’profile.multi_slash’
change -> http_inspect_server: ’non_rfc_char’ ==> ’non_rfc_chars’
change -> http_inspect_server: ’non_strict’ ==> ’profile.non_strict’
change -> http_inspect_server: ’normalize_utf’ ==> ’profile.normalize_utf’
change -> http_inspect_server: ’ports’ ==> ’bindings’
change -> http_inspect_server: ’u_encode’ ==> ’profile.u_encode’
change -> http_inspect_server: ’utf_8’ ==> ’profile.utf_8’
change -> http_inspect_server: ’webroot’ ==> ’profile.webroot’
change -> http_inspect_server: ’whitespace_chars’ ==> ’profile.whitespace_chars’
change -> imap: ’ports’ ==> ’bindings’
change -> paf_max: ’paf_max [0:63780]’ ==> ’max_pdu [1460:63780]’
change -> perfmonitor: ’accumulate’ ==> ’reset = false’
change -> perfmonitor: ’flow-file’ ==> ’flow_file = true’
change -> perfmonitor: ’flow-ip’ ==> ’flow_ip’
change -> perfmonitor: ’flow-ip-file’ ==> ’flow_ip_file = true’
change -> perfmonitor: ’flow-ip-memcap’ ==> ’flow_ip_memcap’
change -> perfmonitor: ’flow-ports’ ==> ’flow_ports’
change -> perfmonitor: ’pktcnt’ ==> ’packets’
change -> perfmonitor: ’snortfile’ ==> ’file = true’
change -> perfmonitor: ’time’ ==> ’seconds’
change -> policy_mode: ’inline_test’ ==> ’inline-test’
change -> pop: ’ports’ ==> ’bindings’
change -> ppm: ’max-pkt-time’ ==> ’max_pkt_time’
change -> ppm: ’max-rule-time’ ==> ’max_rule_time’
change -> ppm: ’pkt-log’ ==> ’pkt_log’
change -> ppm: ’rule-log’ ==> ’rule_log’
change -> ppm: ’suspend-timeout’ ==> ’suspend_timeout’
change -> preprocessor ’normalize_ icmp4’ ==> ’normalize. icmp4’
change -> preprocessor ’normalize_ icmp6’ ==> ’normalize. icmp6’
change -> preprocessor ’normalize_ ip6’ ==> ’normalize. ip6’
change -> profile: ’print’ ==> ’count’
change -> rate_filter: ’gen_id’ ==> ’gid’
change -> rate_filter: ’sig_id’ ==> ’sid’
change -> rule_state: ’disabled’ ==> ’enable’
change -> rule_state: ’enabled’ ==> ’enable’
change -> sfportscan: ’proto’ ==> ’protos’
change -> sfportscan: ’scan_type’ ==> ’scan_types’
change -> sip: ’ports’ ==> ’bindings’
change -> smtp: ’ports’ ==> ’bindings’
change -> ssh: ’server_ports’ ==> ’bindings’
change -> ssl: ’ports’ ==> ’bindings’
change -> stream5_global: ’max_active_responses’ ==> ’max_responses’
change -> stream5_global: ’max_icmp’ ==> ’max_sessions’
Snort 3 User Manual 260 / 284
change -> stream5_global: ’max_ip’ ==> ’max_sessions’
change -> stream5_global: ’max_tcp’ ==> ’max_sessions’
change -> stream5_global: ’max_udp’ ==> ’max_sessions’
change -> stream5_global: ’min_response_seconds’ ==> ’min_interval’
change -> stream5_global: ’prune_log_max’ ==> ’histogram’
change -> stream5_global: ’tcp_cache_nominal_timeout’ ==> ’pruning_timeout’
change -> stream5_global: ’tcp_cache_pruning_timeout’ ==> ’idle_timeout’
change -> stream5_global: ’udp_cache_nominal_timeout’ ==> ’idle_timeout’
change -> stream5_global: ’udp_cache_pruning_timeout’ ==> ’pruning_timeout’
change -> stream5_ip: ’timeout’ ==> ’session_timeout’
change -> stream5_tcp: ’bind_to’ ==> ’bindings’
change -> stream5_tcp: ’dont_reassemble_async’ ==> ’reassemble_async’
change -> stream5_tcp: ’max_queued_bytes’ ==> ’queue_limit.max_bytes’
change -> stream5_tcp: ’max_queued_segs’ ==> ’queue_limit.max_segments’
change -> stream5_tcp: ’policy hpux’ ==> ’stream_tcp.policy = hpux11’
change -> stream5_tcp: ’timeout’ ==> ’session_timeout’
change -> stream5_tcp: ’use_static_footprint_sizes’ ==> ’footprint’
change -> stream5_udp: ’timeout’ ==> ’session_timeout’
change -> suppress: ’gen_id’ ==> ’gid’
change -> suppress: ’sig_id’ ==> ’sid’
change -> syslog: ’log_alert’ ==> ’level = alert’
change -> syslog: ’log_auth’ ==> ’facility = auth’
change -> syslog: ’log_authpriv’ ==> ’facility = authpriv’
change -> syslog: ’log_cons’ ==> ’options = cons’
change -> syslog: ’log_crit’ ==> ’level = crit’
change -> syslog: ’log_daemon’ ==> ’facility = daemon’
change -> syslog: ’log_debug’ ==> ’level = debug’
change -> syslog: ’log_emerg’ ==> ’level = emerg’
change -> syslog: ’log_err’ ==> ’level = err’
change -> syslog: ’log_info’ ==> ’level = info’
change -> syslog: ’log_local0’ ==> ’facility = local0’
change -> syslog: ’log_local1’ ==> ’facility = local1’
change -> syslog: ’log_local2’ ==> ’facility = local2’
change -> syslog: ’log_local3’ ==> ’facility = local3’
change -> syslog: ’log_local4’ ==> ’facility = local4’
change -> syslog: ’log_local5’ ==> ’facility = local5’
change -> syslog: ’log_local6’ ==> ’facility = local6’
change -> syslog: ’log_local7’ ==> ’facility = local7’
change -> syslog: ’log_ndelay’ ==> ’options = ndelay’
change -> syslog: ’log_notice’ ==> ’level = notice’
change -> syslog: ’log_perror’ ==> ’options = perror’
change -> syslog: ’log_pid’ ==> ’options = pid’
change -> syslog: ’log_user’ ==> ’facility = user’
change -> syslog: ’log_warning’ ==> ’level = warning’
change -> threshold: ’ips_option: threshold’ ==> ’event_filter’
change -> unified2: ’ alert_unified2’ ==> ’unified2’
change -> unified2: ’ log_unified2’ ==> ’unified2’
change -> unified2: ’ unified2’ ==> ’unified2’
deleted -> arpspoof: ’unicast’
deleted -> attribute_table: ’<FRAG_POLICY>hpux</FRAG_POLICY>’
deleted -> attribute_table: ’<FRAG_POLICY>irix</FRAG_POLICY>’
deleted -> attribute_table: ’<FRAG_POLICY>old-linux</FRAG_POLICY>’
deleted -> attribute_table: ’<FRAG_POLICY>unknown</FRAG_POLICY>’
deleted -> attribute_table: ’<STREAM_POLICY>noack</STREAM_POLICY>’
deleted -> attribute_table: ’<STREAM_POLICY>unknown</STREAM_POLICY>’
deleted -> config ’ cs_dir’
deleted -> config ’ disable_attribute_reload_thread’
deleted -> config ’ disable_decode_alerts’
deleted -> config ’ disable_decode_drops’
deleted -> config ’ disable_ipopt_alerts’
deleted -> config ’ disable_ipopt_drops’
deleted -> config ’ disable_tcpopt_alerts’
Snort 3 User Manual 261 / 284
deleted -> config ’ disable_tcpopt_drops’
deleted -> config ’ disable_tcpopt_experimental_alerts’
deleted -> config ’ disable_tcpopt_experimental_drops’
deleted -> config ’ disable_tcpopt_obsolete_alerts’
deleted -> config ’ disable_tcpopt_obsolete_drops’
deleted -> config ’ disable_tcpopt_ttcp_alerts’
deleted -> config ’ disable_ttcp_alerts’
deleted -> config ’ disable_ttcp_drops’
deleted -> config ’ dump_dynamic_rules_path’
deleted -> config ’ enable_decode_drops’
deleted -> config ’ enable_decode_oversized_alerts’
deleted -> config ’ enable_decode_oversized_drops’
deleted -> config ’ enable_ipopt_drops’
deleted -> config ’ enable_tcpopt_drops’
deleted -> config ’ enable_tcpopt_experimental_drops’
deleted -> config ’ enable_tcpopt_obsolete_drops’
deleted -> config ’ enable_tcpopt_ttcp_drops’
deleted -> config ’ enable_ttcp_drops’
deleted -> config ’ flexresp2_attempts’
deleted -> config ’ flexresp2_interface’
deleted -> config ’ flexresp2_memcap’
deleted -> config ’ flexresp2_rows’
deleted -> config ’ flowbits_size’
deleted -> config ’ include_vlan_in_alerts’
deleted -> config ’ interface’
deleted -> config ’ layer2resets’
deleted -> config ’ policy_version’
deleted -> config ’ so_rule_memcap’
deleted -> csv: ’<filename> can no longer be specific’
deleted -> csv: ’default’
deleted -> csv: ’trheader’
deleted -> detection: ’mwm’
deleted -> dns: ’enable_experimental_types’
deleted -> dns: ’enable_obsolete_types’
deleted -> dns: ’enable_rdata_overflow’
deleted -> fast: ’<filename> can no longer be specific’
deleted -> frag3_engine: ’detect_anomalies’
deleted -> frag3_global: ’disabled’
deleted -> ftp_telnet_protocol: ’detect_anomalies’
deleted -> full: ’<filename> can no longer be specific’
deleted -> http_inspect: ’disabled’
deleted -> http_inspect_server: ’no_alerts’
deleted -> imap: ’disabled’
deleted -> imap: ’max_mime_mem’
deleted -> imap: ’memcap’
deleted -> perfmonitor: ’atexitonly’
deleted -> perfmonitor: ’atexitonly: base-stats’
deleted -> perfmonitor: ’atexitonly: events-stats’
deleted -> perfmonitor: ’atexitonly: flow-ip-stats’
deleted -> perfmonitor: ’atexitonly: flow-stats’
deleted -> pop: ’disabled’
deleted -> pop: ’max_mime_mem’
deleted -> pop: ’memcap’
deleted -> ppm: ’debug-pkts’
deleted -> react: ’block’
deleted -> react: ’warn’
deleted -> rpc_decode: ’alert_fragments’
deleted -> rpc_decode: ’no_alert_incomplete’
deleted -> rpc_decode: ’no_alert_large_fragments’
deleted -> rpc_decode: ’no_alert_multiple_requests’
deleted -> rule_state: ’action’
deleted -> sfportscan: ’detect_ack_scans’
Snort 3 User Manual 262 / 284
deleted -> sfportscan: ’disabled’
deleted -> sfportscan: ’logfile’
deleted -> sip: ’disabled’
deleted -> smtp: ’alert_unknown_cmds’
deleted -> smtp: ’disabled’
deleted -> smtp: ’enable_mime_decoding’
deleted -> smtp: ’inspection_type’
deleted -> smtp: ’max_mime_depth’
deleted -> smtp: ’max_mime_mem’
deleted -> smtp: ’memcap’
deleted -> smtp: ’no_alerts’
deleted -> smtp: ’print_cmds’
deleted -> ssh: ’autodetect’
deleted -> ssh: ’enable_badmsgdir’
deleted -> ssh: ’enable_paysize’
deleted -> ssh: ’enable_protomismatch’
deleted -> ssh: ’enable_recognition’
deleted -> ssh: ’enable_respoverflow’
deleted -> ssh: ’enable_srvoverflow’
deleted -> ssh: ’enable_ssh1crc32’
deleted -> ssl: ’noinspect_encrypted’
deleted -> stream5_global: ’disabled’
deleted -> stream5_global: ’flush_on_alert’
deleted -> stream5_global: ’no_midstream_drop_alerts’
deleted -> stream5_tcp: ’check_session_hijacking’
deleted -> stream5_tcp: ’detect_anomalies’
deleted -> stream5_tcp: ’dont_store_large_packets’
deleted -> stream5_tcp: ’policy noack’
deleted -> stream5_tcp: ’policy unknown’
deleted -> tcpdump: ’<filename> can no longer be specific’
deleted -> test: ’file’
deleted -> test: ’stdout’
deleted -> unified2: ’filename’
20.11 Module Listing
•ack (ips_option): rule option to match on TCP ack numbers
•active (basic): configure responses
•alert_csv (logger): output event in csv format
•alert_ex (logger): output gid:sid:rev for alerts
•alert_fast (logger): output event with brief text format
•alert_full (logger): output event with full packet dump
•alert_json (logger): output event in json format
•alert_sfsocket (logger): output event over socket
•alert_syslog (logger): output event to syslog
•alert_unixsock (logger): output event over unix socket
•alerts (basic): configure alerts
•appid (inspector): application and service identification
•appids (ips_option): detection option for application ids
•arp (codec): support for address resolution protocol
Snort 3 User Manual 263 / 284
•arp_spoof (inspector): detect ARP attacks and anomalies
•asn1 (ips_option): rule option for asn1 detection
•attribute_table (basic): configure hosts loading
•auth (codec): support for IP authentication header
•back_orifice (inspector): back orifice detection
•base64_decode (ips_option): rule option to decode base64 data - must be used with base64_data option
•binder (inspector): configure processing based on CIDRs, ports, services, etc.
•bufferlen (ips_option): rule option to check length of current buffer
•byte_extract (ips_option): rule option to convert data to an integer variable
•byte_jump (ips_option): rule option to move the detection cursor
•byte_math (ips_option): rule option to perform mathematical operations on extracted value and a specified value or existing
variable
•byte_test (ips_option): rule option to convert data to integer and compare
•ciscometadata (codec): support for cisco metadata
•classifications (basic): define rule categories with priority
•classtype (ips_option): general rule option for rule classification
•content (ips_option): payload rule option for basic pattern matching
•cvs (ips_option): payload rule option for detecting specific attacks
•daq (basic): configure packet acquisition interface
•data_log (inspector): log selected published data to data.log
•dce_http_proxy (inspector): dce over http inspection - client to/from proxy
•dce_http_server (inspector): dce over http inspection - proxy to/from server
•dce_iface (ips_option): detection option to check dcerpc interface
•dce_opnum (ips_option): detection option to check dcerpc operation number
•dce_smb (inspector): dce over smb inspection
•dce_stub_data (ips_option): sets the cursor to dcerpc stub data
•dce_tcp (inspector): dce over tcp inspection
•dce_udp (inspector): dce over udp inspection
•decode (basic): general decoder rules
•detection (basic): configure general IPS rule processing parameters
•detection_filter (ips_option): rule option to require multiple hits before a rule generates an event
•dnp3 (inspector): dnp3 inspection
•dnp3_data (ips_option): sets the cursor to dnp3 data
•dnp3_func (ips_option): detection option to check DNP3 function code
•dnp3_ind (ips_option): detection option to check DNP3 indicator flags
Snort 3 User Manual 264 / 284
•dnp3_obj (ips_option): detection option to check DNP3 object headers
•dns (inspector): dns inspection
•dpx (inspector): dynamic inspector example
•dsize (ips_option): rule option to test payload size
•eapol (codec): support for extensible authentication protocol over LAN
•erspan2 (codec): support for encapsulated remote switched port analyzer - type 2
•erspan3 (codec): support for encapsulated remote switched port analyzer - type 3
•esp (codec): support for encapsulating security payload
•eth (codec): support for ethernet protocol (DLT 1) (DLT 51)
•event_filter (basic): configure thresholding of events
•event_queue (basic): configure event queue parameters
•fabricpath (codec): support for fabricpath
•file_connector (connector): implement the file based connector
•file_data (ips_option): rule option to set detection cursor to file data
•file_id (inspector): configure file identification
•file_log (inspector): log file event to file.log
•file_type (ips_option): rule option to check file type
•flags (ips_option): rule option to test TCP control flags
•flow (ips_option): rule option to check session properties
•flowbits (ips_option): rule option to set and test arbitrary boolean flags
•fragbits (ips_option): rule option to test IP frag flags
•fragoffset (ips_option): rule option to test IP frag offset
•ftp_client (inspector): FTP client configuration module for use with ftp_server
•ftp_data (inspector): FTP data channel handler
•ftp_server (inspector): main FTP module; ftp_client should also be configured
•gid (ips_option): rule option specifying rule generator
•gre (codec): support for generic routing encapsulation
•gtp (codec): support for general-packet-radio-service tunneling protocol
•gtp_info (ips_option): rule option to check gtp info element
•gtp_inspect (inspector): gtp control channel inspection
•gtp_type (ips_option): rule option to check gtp types
•gtp_version (ips_option): rule option to check GTP version
•high_availability (basic): implement flow tracking high availability
•host_cache (basic): configure hosts
•host_tracker (basic): configure hosts
Snort 3 User Manual 265 / 284
•hosts (basic): configure hosts
•http_client_body (ips_option): rule option to set the detection cursor to the request body
•http_cookie (ips_option): rule option to set the detection cursor to the HTTP cookie
•http_header (ips_option): rule option to set the detection cursor to the normalized headers
•http_inspect (inspector): HTTP inspector
•http_method (ips_option): rule option to set the detection cursor to the HTTP request method
•http_raw_body (ips_option): rule option to set the detection cursor to the unnormalized message body
•http_raw_cookie (ips_option): rule option to set the detection cursor to the unnormalized cookie
•http_raw_header (ips_option): rule option to set the detection cursor to the unnormalized headers
•http_raw_request (ips_option): rule option to set the detection cursor to the unnormalized request line
•http_raw_status (ips_option): rule option to set the detection cursor to the unnormalized status line
•http_raw_trailer (ips_option): rule option to set the detection cursor to the unnormalized trailers
•http_raw_uri (ips_option): rule option to set the detection cursor to the unnormalized URI
•http_stat_code (ips_option): rule option to set the detection cursor to the HTTP status code
•http_stat_msg (ips_option): rule option to set the detection cursor to the HTTP status message
•http_trailer (ips_option): rule option to set the detection cursor to the normalized trailers
•http_true_ip (ips_option): rule option to set the detection cursor to the final client IP address
•http_uri (ips_option): rule option to set the detection cursor to the normalized URI buffer
•http_version (ips_option): rule option to set the detection cursor to the version buffer
•icmp4 (codec): support for Internet control message protocol v4
•icmp6 (codec): support for Internet control message protocol v6
•icmp_id (ips_option): rule option to check ICMP ID
•icmp_seq (ips_option): rule option to check ICMP sequence number
•icode (ips_option): rule option to check ICMP code
•id (ips_option): rule option to check the IP ID field
•igmp (codec): support for Internet group management protocol
•imap (inspector): imap inspection
•inspection (basic): configure basic inspection policy parameters
•ip_proto (ips_option): rule option to check the IP protocol number
•ipopts (ips_option): rule option to check for IP options
•ips (basic): configure IPS rule processing
•ipv4 (codec): support for Internet protocol v4
•ipv6 (codec): support for Internet protocol v6
•isdataat (ips_option): rule option to check for the presence of payload data
•itype (ips_option): rule option to check ICMP type
Snort 3 User Manual 266 / 284
•latency (basic): packet and rule latency monitoring and control
•llc (codec): support for logical link control
•log_codecs (logger): log protocols in packet by layer
•log_hext (logger): output payload suitable for daq hext
•log_pcap (logger): log packet in pcap format
•md5 (ips_option): payload rule option for hash matching
•memory (basic): memory management configuration
•metadata (ips_option): rule option for conveying arbitrary name, value data within the rule text
•modbus (inspector): modbus inspection
•modbus_data (ips_option): rule option to set cursor to modbus data
•modbus_func (ips_option): rule option to check modbus function code
•modbus_unit (ips_option): rule option to check Modbus unit ID
•mpls (codec): support for multiprotocol label switching
•msg (ips_option): rule option summarizing rule purpose output with events
•mss (ips_option): detection for TCP maximum segment size
•network (basic): configure basic network parameters
•normalizer (inspector): packet scrubbing for inline mode
•output (basic): configure general output parameters
•packet_capture (inspector): raw packet dumping facility
•packets (basic): configure basic packet handling
•pbb (codec): support for 802.1ah protocol
•pcre (ips_option): rule option for matching payload data with pcre
•perf_monitor (inspector): performance monitoring and flow statistics collection
•pgm (codec): support for pragmatic general multicast
•pkt_data (ips_option): rule option to set the detection cursor to the normalized packet data
•pkt_num (ips_option): alert on raw packet number
•pop (inspector): pop inspection
•port_scan (inspector): detect various ip, icmp, tcp, and udp port or protocol scans
•pppoe (codec): support for point-to-point protocol over ethernet
•priority (ips_option): rule option for prioritizing events
•process (basic): configure basic process setup
•profiler (basic): configure profiling of rules and/or modules
•rate_filter (basic): configure rate filters (which change rule actions)
•raw_data (ips_option): rule option to set the detection cursor to the raw packet data
•react (ips_action): send response to client and terminate session
Snort 3 User Manual 267 / 284
•reference (ips_option): rule option to indicate relevant attack identification system
•references (basic): define reference systems used in rules
•reg_test (inspector): The regression test inspector (rti) is used when special packet handling is required for a reg test
•regex (ips_option): rule option for matching payload data with hyperscan regex
•reject (ips_action): terminate session with TCP reset or ICMP unreachable
•rem (ips_option): rule option to convey an arbitrary comment in the rule body
•replace (ips_option): rule option to overwrite payload data; use with rewrite action
•reputation (inspector): reputation inspection
•rev (ips_option): rule option to indicate current revision of signature
•rewrite (ips_action): overwrite packet contents
•rpc (ips_option): rule option to check SUNRPC CALL parameters
•rpc_decode (inspector): RPC inspector
•rule_state (basic): enable/disable specific IPS rules
•sd_pattern (ips_option): rule option for detecting sensitive data
•search_engine (basic): configure fast pattern matcher
•seq (ips_option): rule option to check TCP sequence number
•service (ips_option): rule option to specify list of services for grouping rules
•session (ips_option): rule option to check user data from TCP sessions
•sha256 (ips_option): payload rule option for hash matching
•sha512 (ips_option): payload rule option for hash matching
•sid (ips_option): rule option to indicate signature number
•side_channel (basic): implement the side-channel asynchronous messaging subsystem
•sip (inspector): sip inspection
•sip_body (ips_option): rule option to set the detection cursor to the request body
•sip_header (ips_option): rule option to set the detection cursor to the SIP header buffer
•sip_method (ips_option): detection option for sip stat code
•sip_stat_code (ips_option): detection option for sip stat code
•smtp (inspector): smtp inspection
•snort (basic): command line configuration and shell commands
•so (ips_option): rule option to call custom eval function
•soid (ips_option): rule option to specify a shared object rule ID
•ssh (inspector): ssh inspection
•ssl (inspector): ssl inspection
•ssl_state (ips_option): detection option for ssl state
•ssl_version (ips_option): detection option for ssl version
Snort 3 User Manual 268 / 284
•stream (inspector): common flow tracking
•stream_file (inspector): stream inspector for file flow tracking and processing
•stream_icmp (inspector): stream inspector for ICMP flow tracking
•stream_ip (inspector): stream inspector for IP flow tracking and defragmentation
•stream_reassemble (ips_option): detection option for stream reassembly control
•stream_size (ips_option): detection option for stream size checking
•stream_tcp (inspector): stream inspector for TCP flow tracking and stream normalization and reassembly
•stream_udp (inspector): stream inspector for UDP flow tracking
•stream_user (inspector): stream inspector for user flow tracking and reassembly
•suppress (basic): configure event suppressions
•tag (ips_option): rule option to log additional packets
•target (ips_option): rule option to indicate target of attack
•tcp (codec): support for transmission control protocol
•tcp_connector (connector): implement the tcp stream connector
•telnet (inspector): telnet inspection and normalization
•token_ring (codec): support for token ring decoding
•tos (ips_option): rule option to check type of service field
•ttl (ips_option): rule option to check time to live field
•udp (codec): support for user datagram protocol
•unified2 (logger): output event and packet in unified2 format file
•urg (ips_option): detection for TCP urgent pointer
•vlan (codec): support for local area network
•window (ips_option): rule option to check TCP window field
•wizard (inspector): inspector that implements port-independent protocol identification
•wlan (codec): support for wireless local area network protocol (DLT 105)
•wscale (ips_option): detection for TCP window scale
20.12 Plugin Listing
•codec::arp: support for address resolution protocol
•codec::auth: support for IP authentication header
•codec::bad_proto: bad protocol id
•codec::ciscometadata: support for cisco metadata
•codec::eapol: support for extensible authentication protocol over LAN
•codec::erspan2: support for encapsulated remote switched port analyzer - type 2
•codec::erspan3: support for encapsulated remote switched port analyzer - type 3
Snort 3 User Manual 269 / 284
•codec::esp: support for encapsulating security payload
•codec::eth: support for ethernet protocol (DLT 1) (DLT 51)
•codec::fabricpath: support for fabricpath
•codec::gre: support for generic routing encapsulation
•codec::gtp: support for general-packet-radio-service tunneling protocol
•codec::icmp4: support for Internet control message protocol v4
•codec::icmp4_ip: support for IP in ICMPv4
•codec::icmp6: support for Internet control message protocol v6
•codec::icmp6_ip: support for IP in ICMPv6
•codec::igmp: support for Internet group management protocol
•codec::ipv4: support for Internet protocol v4
•codec::ipv6: support for Internet protocol v6
•codec::ipv6_dst_opts: support for ipv6 destination options
•codec::ipv6_frag: support for IPv6 fragment decoding
•codec::ipv6_hop_opts: support for IPv6 hop options
•codec::ipv6_mobility: support for mobility
•codec::ipv6_no_next: sentinel codec
•codec::ipv6_routing: support for IPv6 routing extension
•codec::linux_sll: support for Linux SLL (DLT 113)
•codec::llc: support for logical link control
•codec::mpls: support for multiprotocol label switching
•codec::null: support for null encapsulation (DLT 0)
•codec::pbb: support for 802.1ah protocol
•codec::pflog: support for OpenBSD PF log (DLT 117)
•codec::pgm: support for pragmatic general multicast
•codec::ppp: support for point-to-point encapsulation (DLT 9)
•codec::ppp_encap: support for point-to-point encapsulation
•codec::pppoe_disc: support for point-to-point discovery
•codec::pppoe_sess: support for point-to-point session
•codec::raw4: support for unencapsulated IPv4 (DLT 12) (DLT 228)
•codec::raw6: support for unencapsulated IPv6 (DLT 229)
•codec::slip: support for slip protocol (DLT 8)
•codec::tcp: support for transmission control protocol
•codec::teredo: support for teredo
•codec::token_ring: support for token ring decoding
Snort 3 User Manual 270 / 284
•codec::trans_bridge: support for trans-bridging
•codec::udp: support for user datagram protocol
•codec::user: support for user sessions (DLT 230)
•codec::vlan: support for local area network
•codec::wlan: support for wireless local area network protocol (DLT 105)
•connector::file_connector: implement the file based connector
•connector::tcp_connector: implement the tcp stream connector
•inspector::appid: application and service identification
•inspector::arp_spoof: detect ARP attacks and anomalies
•inspector::back_orifice: back orifice detection
•inspector::binder: configure processing based on CIDRs, ports, services, etc.
•inspector::data_log: log selected published data to data.log
•inspector::dce_http_proxy: dce over http inspection - client to/from proxy
•inspector::dce_http_server: dce over http inspection - proxy to/from server
•inspector::dce_smb: dce over smb inspection
•inspector::dce_tcp: dce over tcp inspection
•inspector::dce_udp: dce over udp inspection
•inspector::dnp3: dnp3 inspection
•inspector::dns: dns inspection
•inspector::dpx: dynamic inspector example
•inspector::file_id: configure file identification
•inspector::file_log: log file event to file.log
•inspector::ftp_client: FTP inspector client module
•inspector::ftp_data: FTP data channel handler
•inspector::ftp_server: FTP inspector server module
•inspector::gtp_inspect: gtp control channel inspection
•inspector::http_inspect: the new HTTP inspector!
•inspector::imap: imap inspection
•inspector::modbus: modbus inspection
•inspector::normalizer: packet scrubbing for inline mode
•inspector::packet_capture: raw packet dumping facility
•inspector::perf_monitor: performance monitoring and flow statistics collection
•inspector::pop: pop inspection
•inspector::port_scan: detect various ip, icmp, tcp, and udp port or protocol scans
•inspector::reg_test: The regression test inspector (rti) is used when special packet handling is required for a reg test
Snort 3 User Manual 271 / 284
•inspector::reputation: reputation inspection
•inspector::rpc_decode: RPC inspector
•inspector::sip: sip inspection
•inspector::smtp: smtp inspection
•inspector::ssh: ssh inspection
•inspector::ssl: ssl inspection
•inspector::stream: common flow tracking
•inspector::stream_file: stream inspector for file flow tracking and processing
•inspector::stream_icmp: stream inspector for ICMP flow tracking
•inspector::stream_ip: stream inspector for IP flow tracking and defragmentation
•inspector::stream_tcp: stream inspector for TCP flow tracking and stream normalization and reassembly
•inspector::stream_udp: stream inspector for UDP flow tracking
•inspector::stream_user: stream inspector for user flow tracking and reassembly
•inspector::telnet: telnet inspection and normalization
•inspector::wizard: inspector that implements port-independent protocol identification
•ips_action::react: send response to client and terminate session
•ips_action::reject: terminate session with TCP reset or ICMP unreachable
•ips_action::rewrite: overwrite packet contents
•ips_option::ack: rule option to match on TCP ack numbers
•ips_option::appids: detection option for application ids
•ips_option::asn1: rule option for asn1 detection
•ips_option::base64_data: set detection cursor to decoded Base64 data
•ips_option::base64_decode: rule option to decode base64 data - must be used with base64_data option
•ips_option::bufferlen: rule option to check length of current buffer
•ips_option::byte_extract: rule option to convert data to an integer variable
•ips_option::byte_jump: rule option to move the detection cursor
•ips_option::byte_math: rule option to perform mathematical operations on extracted value and a specified value or existing
variable
•ips_option::byte_test: rule option to convert data to integer and compare
•ips_option::classtype: general rule option for rule classification
•ips_option::content: payload rule option for basic pattern matching
•ips_option::cvs: payload rule option for detecting specific attacks
•ips_option::dce_iface: detection option to check dcerpc interface
•ips_option::dce_opnum: detection option to check dcerpc operation number
•ips_option::dce_stub_data: sets the cursor to dcerpc stub data
Snort 3 User Manual 272 / 284
•ips_option::detection_filter: rule option to require multiple hits before a rule generates an event
•ips_option::dnp3_data: sets the cursor to dnp3 data
•ips_option::dnp3_func: detection option to check DNP3 function code
•ips_option::dnp3_ind: detection option to check DNP3 indicator flags
•ips_option::dnp3_obj: detection option to check DNP3 object headers
•ips_option::dsize: rule option to test payload size
•ips_option::file_data: rule option to set detection cursor to file data
•ips_option::file_type: rule option to check file type
•ips_option::flags: rule option to test TCP control flags
•ips_option::flow: rule option to check session properties
•ips_option::flowbits: rule option to set and test arbitrary boolean flags
•ips_option::fragbits: rule option to test IP frag flags
•ips_option::fragoffset: rule option to test IP frag offset
•ips_option::gid: rule option specifying rule generator
•ips_option::gtp_info: rule option to check gtp info element
•ips_option::gtp_type: rule option to check gtp types
•ips_option::gtp_version: rule option to check GTP version
•ips_option::http_client_body: rule option to set the detection cursor to the request body
•ips_option::http_cookie: rule option to set the detection cursor to the HTTP cookie
•ips_option::http_header: rule option to set the detection cursor to the normalized headers
•ips_option::http_method: rule option to set the detection cursor to the HTTP request method
•ips_option::http_raw_body: rule option to set the detection cursor to the unnormalized message body
•ips_option::http_raw_cookie: rule option to set the detection cursor to the unnormalized cookie
•ips_option::http_raw_header: rule option to set the detection cursor to the unnormalized headers
•ips_option::http_raw_request: rule option to set the detection cursor to the unnormalized request line
•ips_option::http_raw_status: rule option to set the detection cursor to the unnormalized status line
•ips_option::http_raw_trailer: rule option to set the detection cursor to the unnormalized trailers
•ips_option::http_raw_uri: rule option to set the detection cursor to the unnormalized URI
•ips_option::http_stat_code: rule option to set the detection cursor to the HTTP status code
•ips_option::http_stat_msg: rule option to set the detection cursor to the HTTP status message
•ips_option::http_trailer: rule option to set the detection cursor to the normalized trailers
•ips_option::http_true_ip: rule option to set the detection cursor to the final client IP address
•ips_option::http_uri: rule option to set the detection cursor to the normalized URI buffer
•ips_option::http_version: rule option to set the detection cursor to the version buffer
•ips_option::icmp_id: rule option to check ICMP ID
Snort 3 User Manual 273 / 284
•ips_option::icmp_seq: rule option to check ICMP sequence number
•ips_option::icode: rule option to check ICMP code
•ips_option::id: rule option to check the IP ID field
•ips_option::ip_proto: rule option to check the IP protocol number
•ips_option::ipopts: rule option to check for IP options
•ips_option::isdataat: rule option to check for the presence of payload data
•ips_option::itype: rule option to check ICMP type
•ips_option::md5: payload rule option for hash matching
•ips_option::metadata: rule option for conveying arbitrary name, value data within the rule text
•ips_option::modbus_data: rule option to set cursor to modbus data
•ips_option::modbus_func: rule option to check modbus function code
•ips_option::modbus_unit: rule option to check Modbus unit ID
•ips_option::msg: rule option summarizing rule purpose output with events
•ips_option::mss: detection for TCP maximum segment size
•ips_option::pcre: rule option for matching payload data with pcre
•ips_option::pkt_data: rule option to set the detection cursor to the normalized packet data
•ips_option::pkt_num: alert on raw packet number
•ips_option::priority: rule option for prioritizing events
•ips_option::raw_data: rule option to set the detection cursor to the raw packet data
•ips_option::reference: rule option to indicate relevant attack identification system
•ips_option::regex: rule option for matching payload data with hyperscan regex
•ips_option::rem: rule option to convey an arbitrary comment in the rule body
•ips_option::replace: rule option to overwrite payload data; use with rewrite action
•ips_option::rev: rule option to indicate current revision of signature
•ips_option::rpc: rule option to check SUNRPC CALL parameters
•ips_option::sd_pattern: rule option for detecting sensitive data
•ips_option::seq: rule option to check TCP sequence number
•ips_option::service: rule option to specify list of services for grouping rules
•ips_option::session: rule option to check user data from TCP sessions
•ips_option::sha256: payload rule option for hash matching
•ips_option::sha512: payload rule option for hash matching
•ips_option::sid: rule option to indicate signature number
•ips_option::sip_body: rule option to set the detection cursor to the request body
•ips_option::sip_header: rule option to set the detection cursor to the SIP header buffer
•ips_option::sip_method: detection option for sip stat code
Snort 3 User Manual 274 / 284
•ips_option::sip_stat_code: detection option for sip stat code
•ips_option::so: rule option to call custom eval function
•ips_option::soid: rule option to specify a shared object rule ID
•ips_option::ssl_state: detection option for ssl state
•ips_option::ssl_version: detection option for ssl version
•ips_option::stream_reassemble: detection option for stream reassembly control
•ips_option::stream_size: detection option for stream size checking
•ips_option::tag: rule option to log additional packets
•ips_option::target: rule option to indicate target of attack
•ips_option::tos: rule option to check type of service field
•ips_option::ttl: rule option to check time to live field
•ips_option::urg: detection for TCP urgent pointer
•ips_option::window: rule option to check TCP window field
•ips_option::wscale: detection for TCP window scale
•logger::alert_csv: output event in csv format
•logger::alert_ex: output gid:sid:rev for alerts
•logger::alert_fast: output event with brief text format
•logger::alert_full: output event with full packet dump
•logger::alert_json: output event in json format
•logger::alert_sfsocket: output event over socket
•logger::alert_syslog: output event to syslog
•logger::alert_unixsock: output event over unix socket
•logger::log_codecs: log protocols in packet by layer
•logger::log_hext: output payload suitable for daq hext
•logger::log_null: disable logging of packets
•logger::log_pcap: log packet in pcap format
•logger::unified2: output event and packet in unified2 format file
•piglet::pp_codec: Codec piglet
•piglet::pp_inspector: Inspector piglet
•piglet::pp_ips_action: Ips action piglet
•piglet::pp_ips_option: Ips option piglet
•piglet::pp_logger: Logger piglet
•piglet::pp_search_engine: Search engine piglet
•piglet::pp_so_rule: SO rule piglet
•piglet::pp_test: Test piglet
Snort 3 User Manual 275 / 284
•search_engine::ac_banded: Aho-Corasick Banded (high memory, moderate performance)
•search_engine::ac_bnfa: Aho-Corasick Binary NFA (low memory, high performance) MPSE
•search_engine::ac_full: Aho-Corasick Full (high memory, best performance), implements search_all()
•search_engine::ac_sparse: Aho-Corasick Sparse (high memory, moderate performance) MPSE
•search_engine::ac_sparse_bands: Aho-Corasick Sparse-Banded (high memory, moderate performance) MPSE
•search_engine::ac_std: Aho-Corasick Full (high memory, best performance) MPSE
•search_engine::hyperscan: intel hyperscan-based mpse with regex support
•search_engine::lowmem: Keyword Trie (low memory, moderate performance) MPSE
•so_rule::3|18758: SO rule example
20.13 Bugs
20.13.1 Build
• Enabling large pcap may erroneously affect the number of packets processed from pcaps.
• Enabling debug messages may erroneously affect the number of packets processed from pcaps.
• Building with clang and autotools on Linux will show the following warning many times. Please ignore.
clang: warning: argument unused during compilation: ’-pthread’
20.13.2 Config
• Parsing issue with IP lists. can’t parse rules with $EXTERNAL_NET defined as below because of the space between ! and 10.
HOME_NET = [[ 10.0.17.0/24 10.0.14.0/24 10.247.0.0/16 10.246.0.0/16 ]]
EXTERNAL_NET = ’! ’ .. HOME_NET
• Multiple versions of luajit scripts are not handled correctly. The first loaded version will always be executed even though
plugin manager saves the correct version.
• When using -c and -L together, the last on the command line wins (-c -L will dump; -L -c will analyze).
• Modules instantiated by command line only will not get default settings unless hard-coded. This notably applies to -A and -L
options.
• --lua can only be used in addition to, not in place of, a -c config. Ideally, --lua could be used in lieu of -c.
20.13.3 Rules
• metdata:service foo; metadata:service foo; won’t cause a duplicate service warning as does metadata:service foo, service foo;
• ip_proto doesn’t work properly with reassembled packets so it can’t be used to restrict the protocol of service rules.
Snort 3 User Manual 276 / 284
20.13.4 snort2lua
• uricontent:"foo"; content:"bar"; →http_uri; content:"foo"; content:"bar"; (missing pkt_data)
• stream_tcp ports and protocols both go into a single binder.when; this is incorrect as the when fields are logically anded together
(ie must all be true). Should create 2 separate bindings.
• There is a bug in pps_stream_tcp.cc.. when stream_tcp: is specified without any arguments, snort2lua doesn’t convert it. Same
for stream_udp.
• Loses the ip list delimiters [ ]; change to ( )
in snort.conf: var HOME_NET [A,B,C]
in snort.lua: HOME_NET = [[A B C]]
• Won’t convert packet rules (alert tcp etc.) to service rules (alert http etc.).
• alert_fast and alert_full: output configuration includes "file = foo.bar", but file is a bool and you cannot specify an output file
name in the configuration.
20.13.5 Runtime
• -B <mask> feature does not work. It does ordinary IP address obfuscation instead of using the mask.
• Obfuscation does not work for csv format.
• The hext DAQ will append a newline to text lines (starting with ").
• The hext DAQ does not support embedded quotes in text lines (use hex lines as a workaround).
• stream_tcp alert squash mechanism incorrectly squashes alerts for different TCP packets.
20.14 LibDAQ and DAQ Modules
Snort 2.9 introduces the DAQ, or Data Acquisition library, for packet I/O. The DAQ replaces direct calls to libpcap functions
with an abstraction layer that facilitates operation on a variety of hardware and software interfaces without requiring changes to
Snort. It is possible to select the DAQ type and mode when invoking Snort to perform pcap readback or inline operation, etc. The
DAQ library may be useful for other packet processing applications and the modular nature allows you to build new modules for
other platforms.
This README summarizes the important things you need to know to use the DAQ.
20.14.1 Building the DAQ Library and DAQ Modules
The DAQ is bundled with Snort but must be built first using these steps:
./configure
make
sudo make install
This will build and install both static and dynamic DAQ modules.
Note that pcap >= 1.5.0 is required. pcap 1.8.1 is available at the time of this writing and is recommended.
Also, libdnet is required for IPQ and NFQ DAQs. If you get a relocation error trying to build those DAQs, you may need to
reinstall libdnet and configure it with something like this:
./configure "CFLAGS=-fPIC -g -O2"
Snort 3 User Manual 277 / 284
You may also experience problems trying to find the dynamic dnet library because it isn’t always named properly. Try creating a
link to the shared library (identified by its .x or .x.y etc. extension) with the same name but with ".so" inserted as follows:
$ ln -s libdnet.1.1 libdnet.so.1.1
$ ldconfig -Rv /usr/local/lib 2>&1 | grep dnet
Adding /usr/local/lib/libdnet.so.1.1
Alternatively, you should be able to fix both issues as follows:
libtoolize --copy --force
aclocal -I config
autoheader
autoconf
automake --foreign
When the DAQ library is built, both static and dynamic flavors will be generated. The various DAQ modules will be built if the
requisite headers and libraries are available. You can disable individual modules, etc. with options to configure. For the complete
list of configure options, run:
./configure --help
20.14.2 PCAP Module
pcap is the default DAQ. If snort is run w/o any DAQ arguments, it will operate as it always did using this module. These are
equivalent:
./snort -i <device>
./snort -r <file>
./snort --daq pcap --daq-mode passive -i <device>
./snort --daq pcap --daq-mode read-file -r <file>
You can specify the buffer size pcap uses with:
./snort --daq pcap --daq-var buffer_size=<#bytes>
Immediate (less-buffered or unbuffered) delivery mode can be enabled with:
./snort --daq pcap --daq-var immediate=1
This immediate delivery mode can be particularly useful on modern Linux systems with TPACKET_V3 support. LibPCAP will
attempt to use this mode when it is available, but it introduces some potentially undesirable behavior in exchange for better
performance. The most notable behavior change is that the packet timeout will never occur if packets are not being received,
causing the poll() to potentially hang indefinitely. Enabling immediate delivery mode will cause LibPCAP to use TPACKET_V2
instead of TPACKET_V3.
• The pcap DAQ does not count filtered packets. *
20.14.3 AFPACKET Module
afpacket functions similar to the pcap DAQ but with better performance:
./snort --daq afpacket -i <device>
[--daq-var buffer_size_mb=<#MB>]
[--daq-var debug]
Snort 3 User Manual 278 / 284
If you want to run afpacket in inline mode, you must craft the device string as one or more interface pairs, where each member
of a pair is separated by a single colon and each pair is separated by a double colon like this:
eth0:eth1
or this:
eth0:eth1::eth2:eth3
By default, the afpacket DAQ allocates 128MB for packet memory. You can change this with:
--daq-var buffer_size_mb=<#MB>
Note that the total allocated is actually higher, here’s why. Assuming the default packet memory with a snaplen of 1518, the
numbers break down like this:
• The frame size is 1518 (snaplen) + the size of the AFPacket header (66 bytes) = 1584 bytes.
• The number of frames is 128 MB / 1518 = 84733.
• The smallest block size that can fit at least one frame is 4 KB = 4096 bytes @ 2 frames per block.
• As a result, we need 84733 / 2 = 42366 blocks.
• Actual memory allocated is 42366 * 4 KB = 165.5 MB.
Note
Linux kernel version 2.6.31 or higher is required for the AFPacket DAQ module due to its dependency on both TPACKET v2
and PACKET_TX_RING support.
Fanout (Kernel Loadbalancing)
More recent Linux kernel versions (3.1+) support various kernel-space loadbalancing methods within AFPacket configured using
the PACKET_FANOUT ioctl. This allows you to have multiple AFPacket DAQ module instances processing packets from the
same interfaces in parallel for significantly improved throughput.
To configure PACKET_FANOUT in the AFPacket DAQ module, two DAQ variables are used:
--daq-var fanout_type=<hash|lb|cpu|rollover|rnd|qm>
and (optionally):
--daq-var fanout_flag=<rollover|defrag>
In general, you’re going to want to use the hash fanout type, but the others have been included for completeness. The defrag
fanout flag is probably a good idea to correctly handle loadbalancing of flows containing fragmented packets.
Please read the man page for packet or packet_mmap.txt in the Linux kernel source for more details on the different fanout types
and modifier flags.
20.14.4 NFQ Module
NFQ is the new and improved way to process iptables packets:
./snort --daq nfq \
[--daq-var device=<dev>] \
[--daq-var proto=<proto>] \
[--daq-var queue=<qid>]
Snort 3 User Manual 279 / 284
<dev> ::= ip | eth0, etc; default is IP injection
<proto> ::= ip4 | ip6 |; default is ip4
<qid> ::= 0..65535; default is 0
This module can not run unprivileged so ./snort -u -g will produce a warning and won’t change user or group.
Notes on iptables are given below.
20.14.5 IPQ Module
IPQ is the old way to process iptables packets. It replaces the inline version available in pre-2.9 versions built with this:
./configure --enable-inline
Note that layer 2 resets are not supported with the IPQ DAQ:
config layer2resets[: <mac>]
Start the IPQ DAQ as follows:
./snort --daq ipq \
[--daq-var device=<dev>] \
[--daq-var proto=<proto>] \
<dev> ::= ip | eth0, etc; default is IP injection
<proto> ::= ip4 | ip6; default is ip4
This module can not run unprivileged so ./snort -u -g will produce a warning and won’t change user or group.
Notes on iptables are given below.
20.14.6 IPFW Module
IPFW is available for BSD systems. It replaces the inline version available in pre-2.9 versions built with this:
./configure --enable-ipfw
This command line argument is no longer supported:
./snort -J <port#>
Instead, start Snort like this:
./snort --daq ipfw [--daq-var port=<port>]
<port> ::= 1..65535; default is 8000
• IPFW only supports ip4 traffic.
Notes on FreeBSD and OpenBSD are given below.
Snort 3 User Manual 280 / 284
20.14.7 Dump Module
The dump DAQ allows you to test the various inline mode features available in 2.9 Snort like injection and normalization.
./snort -i <device> --daq dump
./snort -r <pcap> --daq dump
By default a file named inline-out.pcap will be created containing all packets that passed through or were generated by snort.
You can optionally specify a different name.
./snort --daq dump --daq-var file=<name>
The dump DAQ also supports text output of verdicts rendered, injected packets, and other such items. In order to enable text
output, the output DAQ variable must be set to either text (text output only) or both (both text and PCAP output will be written).
The default filename for the text output is inline-out.txt, but it can be overridden like so:
./snort --daq dump --daq-var output=text --daq-var text-file=<filename>
dump uses the pcap daq for packet acquisition. It therefore does not count filtered packets (a pcap limitation).
Note that the dump DAQ inline mode is not an actual inline mode. Furthermore, you will probably want to have the pcap DAQ
acquire in another mode like this:
./snort -r <pcap> -Q --daq dump --daq-var load-mode=read-file
./snort -i <device> -Q --daq dump --daq-var load-mode=passive
20.14.8 Netmap Module
The netmap project is a framework for very high speed packet I/O. It is available on both FreeBSD and Linux with varying
amounts of preparatory setup required. Specific notes for each follow.
./snort --daq netmap -i <device>
[--daq-var debug]
If you want to run netmap in inline mode, you must craft the device string as one or more interface pairs, where each member of
a pair is separated by a single colon and each pair is separated by a double colon like this:
em1:em2
or this:
em1:em2::em3:em4
Inline operation performs Layer 2 forwarding with no MAC filtering, akin to the AFPacket module’s behavior. All packets
received on one interface in an inline pair will be forwarded out the other interface unless dropped by the reader and vice versa.
Important
The interfaces will need to be up and in promiscuous mode in order to function (ifconfig em1 up promisc). The DAQ
module does not currently do either of these configuration steps for itself.
FreeBSD
In FreeBSD 10.0, netmap has been integrated into the core OS. In order to use it, you must recompile your kernel with the line
device netmap
added to your kernel config.
Snort 3 User Manual 281 / 284
Linux
You will need to download the netmap source code from the project’s repository:
https://code.google.com/p/netmap/
Follow the instructions on the project’s homepage for compiling and installing the code:
http://info.iet.unipi.it/~luigi/netmap/
It will involve a standalone kernel module (netmap_lin) as well as patching and rebuilding the kernel module used to drive your
network adapters. The following drivers are supported under Linux at the time of writing (June 2014):
e1000
e1000e
forcedeth
igb
ixgbe
r8169
virtio
TODO: - Support for attaching to only a single ring (queue) on a network adapter. - Support for VALE and netmap pipes.
20.14.9 Notes on iptables
These notes are just a quick reminder that you need to set up iptables to use the IPQ or NFQ DAQs. Doing so may cause problems
with your network so tread carefully. The examples below are intentionally incomplete so please read the related documentation
first.
Here is a blog post by Marty for historical reference:
http://archives.neohapsis.com/archives/snort/2000-11/0394.html
You can check this out for queue sizing tips:
http://www.inliniac.net/blog/2008/01/23/improving-snort_inlines-nfq-performance. ←-
html
You might find useful IPQ info here:
http://snort-inline.sourceforge.net/
Use this to examine your iptables:
sudo /sbin/iptables -L
Use something like this to set up NFQ:
sudo /sbin/iptables
-I <table> [<protocol stuff>] [<state stuff>]
-j NFQUEUE --queue-num 1
Use something like this to set up IPQ:
sudo iptables -I FORWARD -j QUEUE
Use something like this to "disconnect" snort:
sudo /sbin/iptables -D <table> <rule pos>
Snort 3 User Manual 282 / 284
Be sure to start Snort prior to routing packets through NFQ with iptables. Such packets will be dropped until Snort is started.
The queue-num is the number you must give Snort.
If you are running on a system with both NFQ and IPQ support, you may experience some start-up failures of the sort:
The solution seems to be to remove both modules from the kernel like this:
modprobe -r nfnetlink_queue
modprobe -r ip_queue
and then install the module you want:
modprobe ip_queue
or:
modprobe nfnetlink_queue
These DAQs should be run with a snaplen of 65535 since the kernel defrags the packets before queuing. Also, no need to
configure frag3.
20.14.10 Notes on FreeBSD::IPFW
Check the online manual at:
http://www.freebsd.org/doc/handbook/firewalls-ipfw.html.
Here is a brief example to divert icmp packets to Snort at port 8000:
To enable support for divert sockets, place the following lines in the kernel configuration file:
options IPFIREWALL
options IPDIVERT
(The file in this case was: /usr/src/sys/i386/conf/GENERIC; which is platform dependent.)
You may need to also set these to use the loadable kernel modules:
/etc/rc.conf:
firewall_enable="YES"
/boot/loader.conf:
ipfw_load="YES"
ipdivert_load="YES"
$ dmesg | grep ipfw
ipfw2 (+ipv6) initialized, divert loadable, nat loadable, rule-based
forwarding disabled, default to deny, logging disabled
$ kldload -v ipdivert
Loaded ipdivert, id=4
$ ipfw add 75 divert 8000 icmp from any to any
00075 divert 8000 icmp from any to any
Snort 3 User Manual 283 / 284
$ ipfw list
...
00075 divert 8000 icmp from any to any
00080 allow icmp from any to any
...
• Note that on FreeBSD, divert sockets don’t work with bridges!
Please refer to the following articles for more information:
https://forums.snort.org/forums/support/topics/snort-inline-on-freebsd-ipfw http://freebsd.rogness.net/snort_inline/
NAT gateway can be used with divert sockets if the network environment is conducive to using NAT.
The steps to set up NAT with ipfw are as follows:
1. Set up NAT with two interface em0 and em1 by adding the following to /etc/rc.conf. Here em0 is connected to external
network and em1 to host-only LAN.
gateway_enable="YES"
natd_program="/sbin/natd" # path to natd
natd_enable="YES" # Enable natd (if firewall_enable == YES)
natd_interface="em0" # Public interface or IP Address
natd_flags="-dynamic" # Additional flags
defaultrouter=""
ifconfig_em0="DHCP"
ifconfig_em1="inet 192.168.1.2 netmask 255.255.255.0"
firewall_enable="YES"
firewall_script="/etc/rc.firewall"
firewall_type="simple"
2. Add the following divert rules to divert packets to Snort above and below the NAT rule in the "Simple" section of
/etc/rc.firewall.
...
# Inspect outbound packets (those arriving on "inside" interface)
# before NAT translation.
${fwcmd} add divert 8000 all from any to any in via ${iif}
case ${natd_enable} in
[Yy][Ee][Ss])
if [ -n "${natd_interface}" ]; then
${fwcmd} add divert natd all from any to any via
${natd_interface}
fi
;;
esac
...
# Inspect inbound packets (those arriving on "outside" interface)
# after NAT translation that aren’t blocked for other reasons,
# after the TCP "established" rule.
${fwcmd} add divert 8000 all from any to any in via ${oif}
20.14.11 Notes on OpenBSD::IPFW
OpenBSD supports divert sockets as of 4.7, so we use the ipfw DAQ.
Here is one way to set things up:
Snort 3 User Manual 284 / 284
1. Configure the system to forward packets:
$ sysctl net.inet.ip.forwarding=1
$ sysctl net.inet6.ip6.forwarding=1
(You can also put that in /etc/sysctl.conf to enable on boot.)
2. Set up interfaces
$ dhclient vic1
$ dhclient vic2
3. Set up packet filter rules:
$ echo "pass out on vic1 divert-packet port 9000 keep-state" > rules.txt
$ echo "pass out on vic2 divert-packet port 9000 keep-state" >> rules.txt
$ pfctl -v -f rules.txt
4. Analyze packets diverted to port 9000:
$ ./snort --daq ipfw --daq-var port=9000
• Note that on OpenBSD, divert sockets don’t work with bridges!

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