Nmap Cookbook The Fat Free Guide To Network Scanning

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Nmap® Cookbook

The fat-free guide to network scanning

Nmap® Cookbook

The Fat-free Guide to Network Scanning

ISBN: 1449902529

EAN-13: 9781449902520

www.NmapCookbook.com

BSD® is a registered trademark of the University of California, Berkeley

CentOS is property of CentOS Ltd.

Debian® is a registered trademark of Software in the Public Interest, Inc

Fedora® is a registered trademark of Red Hat, Inc.

FreeBSD® is a registered trademark of The FreeBSD Foundation

Gentoo® is a registered trademark of The Gentoo Foundation

Linux® is the registered trademark of Linus Torvalds

Mac OS X® is a registered trademark of Apple, Inc.

Windows® is a registered trademark of Microsoft Corporation

Nmap® is a registered trademark of Insecure.Com LLC

Red Hat® is a registered trademark of Red Hat, Inc.

Ubuntu® is a registered trademark of Canonical Ltd.

UNIX® is a registered trademark of The Open Group

All other trademarks used in this book are property of their respective owners. Use

of any trademark in this book does not constitute an affiliation with or endorsement

from the trademark holder.

All information in this book is presented on an “as-is” basis. No warranty or

guarantee is provided and the author and/or publisher shall not be held liable for

any loss or damage.

Contents at a Glance

Introduction....................................................................................... 15

Section 1: Installing Nmap .................................................................. 19

Section 2: Basic Scanning Techniques .................................................. 33

Section 3: Discovery Options .............................................................. 45

Section 4: Advanced Scanning Options ................................................ 65

Section 5: Port Scanning Options ........................................................ 79

Section 6: Operating System and Service Detection ............................. 89

Section 7: Timing Options .................................................................. 97

Section 8: Evading Firewalls .............................................................. 115

Section 9: Output Options ................................................................ 127

Section 10: Troubleshooting and Debugging ...................................... 135

Section 11: Zenmap .......................................................................... 147

Section 12: Nmap Scripting Engine (NSE)........................................... 161

Section 13: Ndiff .............................................................................. 171

Section 14: Tips and Tricks ................................................................ 177

Appendix A - Nmap Cheat Sheet ....................................................... 187

Appendix B - Nmap Port States ......................................................... 191

Appendix C - CIDR Cross Reference ................................................... 193

Appendix D - Common TCP/IP Ports .................................................. 195

Table of Contents

Introduction....................................................................................... 15

Conventions Used In This Book ............................................................. 18

Section 1: Installing Nmap .................................................................. 19

Installation Overview ............................................................................ 20

Installing Nmap on Windows ................................................................ 21

Installing Nmap on Unix and Linux systems .......................................... 25

Installing Precompiled Packages for Linux ........................................ 25

Compiling Nmap from Source for Unix and Linux ............................ 26

Installing Nmap on Mac OS X ................................................................ 29

Section 2: Basic Scanning Techniques .................................................. 33

Basic Scanning Overview ....................................................................... 34

Scan a Single Target............................................................................... 35

Scan Multiple Targets ............................................................................ 36

Scan a Range of IP Addresses ................................................................ 37

Scan an Entire Subnet ........................................................................... 38

Scan a List of Targets ............................................................................. 39

Scan Random Targets ............................................................................ 40

Exclude Targets from a Scan.................................................................. 41

Exclude Targets Using a List .................................................................. 42

Perform an Aggressive Scan .................................................................. 43

Scan an IPv6 Target ............................................................................... 44

Section 3: Discovery Options .............................................................. 45

Discovery Options Overview ................................................................. 46

Don’t Ping ............................................................................................. 47

Ping Only Scan ....................................................................................... 48

TCP SYN Ping ......................................................................................... 49

TCP ACK Ping ......................................................................................... 50

UDP Ping ............................................................................................... 51

SCTP INIT Ping ....................................................................................... 52

ICMP Echo Ping ..................................................................................... 53

ICMP Timestamp Ping .......................................................................... 54

ICMP Address Mask Ping ...................................................................... 55

IP Protocol Ping .................................................................................... 56

ARP Ping ............................................................................................... 57

Traceroute ............................................................................................ 58

Force Reverse DNS Resolution.............................................................. 59

Disable Reverse DNS Resolution ........................................................... 60

Alternative DNS Lookup Method.......................................................... 61

Manually Specify DNS Server(s) ........................................................... 62

Create a Host List .................................................................................. 63

Section 4: Advanced Scanning Options ................................................ 65

Advanced Scanning Functions Overview .............................................. 66

TCP SYN Scan ........................................................................................ 67

TCP Connect Scan ................................................................................. 68

UDP Scan .............................................................................................. 69

TCP NULL Scan ...................................................................................... 70

TCP FIN Scan ......................................................................................... 71

Xmas Scan ............................................................................................. 72

Custom TCP Scan .................................................................................. 73

TCP ACK Scan ........................................................................................ 74

IP Protocol Scan .................................................................................... 75

Send Raw Ethernet Packets .................................................................. 76

Send IP Packets ..................................................................................... 77

Section 5: Port Scanning Options ........................................................ 79

Port Scanning Options Overview .......................................................... 80

Perform a Fast Scan .............................................................................. 81

Scan Specific Ports ................................................................................ 82

Scan Ports by Name .............................................................................. 83

Scan Ports by Protocol .......................................................................... 84

Scan All Ports......................................................................................... 85

Scan Top Ports ....................................................................................... 86

Perform a Sequential Port Scan ............................................................ 87

Section 6: Operating System and Service Detection ............................. 89

Version Detection Overview ................................................................. 90

Operating System Detection ................................................................. 91

Submitting TCP/IP Fingerprints ............................................................. 92

Attempt to Guess an Unknown Operating System ............................... 93

Service Version Detection ..................................................................... 94

Troubleshooting Version Scans ............................................................. 95

Perform an RPC Scan ............................................................................. 96

Section 7: Timing Options .................................................................. 97

Timing Options Overview ..................................................................... 98

Timing Parameters ................................................................................ 99

Timing Templates ................................................................................ 100

Minimum Number of Parallel Operations........................................... 101

Maximum Number of Parallel Operations .......................................... 102

Minimum Host Group Size .................................................................. 103

Maximum Host Group Size ................................................................. 104

Initial RTT Timeout ............................................................................. 105

Maximum RTT Timeout ...................................................................... 106

Maximum Retries ................................................................................ 107

Set the Packet TTL ............................................................................... 108

Host Timeout ...................................................................................... 109

Minimum Scan Delay .......................................................................... 110

Maximum Scan Delay .......................................................................... 111

Minimum Packet Rate ......................................................................... 112

Maximum Packet Rate ........................................................................ 113

Defeat Reset Rate Limits ..................................................................... 114

Section 8: Evading Firewalls .............................................................. 115

Firewall Evasion Techniques Overview ............................................... 116

Fragment Packets ............................................................................... 117

Specify a Specific MTU ....................................................................... 118

Use a Decoy ........................................................................................ 119

Idle Zombie Scan ................................................................................ 120

Manually Specify a Source Port Number ............................................ 121

Append Random Data ........................................................................ 122

Randomize Target Scan Order ............................................................ 123

Spoof MAC Address ............................................................................ 124

Send Bad Checksums .......................................................................... 125

Section 9: Output Options ................................................................ 127

Output Options Overview .................................................................. 128

Save Output to a Text File................................................................... 129

Save Output to a XML File .................................................................. 130

Grepable Output ................................................................................ 131

Output All Supported File Types......................................................... 132

Display Scan Statistics ......................................................................... 133

133t Output ........................................................................................ 134

Section 10: Troubleshooting and Debugging ...................................... 135

Troubleshooting and Debugging Overview ........................................ 136

Getting Help ....................................................................................... 137

Display Nmap Version ......................................................................... 138

Verbose Output .................................................................................. 139

Debugging .......................................................................................... 140

Display Port State Reason Codes ........................................................ 141

Only Display Open Ports ..................................................................... 142

Trace Packets ...................................................................................... 143

Display Host Networking Configuration ............................................. 144

Specify Which Network Interface to Use ........................................... 145

Section 11: Zenmap .......................................................................... 147

Zenmap Overview ............................................................................... 148

Launching Zenmap .............................................................................. 149

Basic Zenmap Operations ................................................................... 150

Zenmap Results ................................................................................... 151

Scanning Profiles ................................................................................. 152

Profile Editor ....................................................................................... 153

Viewing Open Ports ............................................................................ 154

Viewing a Network Map ..................................................................... 155

Saving Network Maps ......................................................................... 156

Viewing Host Details ........................................................................... 157

Viewing Scan History .......................................................................... 158

Comparing Scan Results ...................................................................... 159

Saving Scans ........................................................................................ 160

Section 12: Nmap Scripting Engine (NSE)........................................... 161

Nmap Scripting Engine Overview........................................................ 162

Execute Individual Scripts ................................................................... 163

Execute Multiple Scripts ..................................................................... 164

Script Categories ................................................................................. 165

Execute Scripts by Category ................................................................ 166

Execute Multiple Script Categories ..................................................... 167

Troubleshoot Scripts ........................................................................... 168

Update the Script Database ................................................................ 169

Section 13: Ndiff .............................................................................. 171

Ndiff Overview .................................................................................... 172

Scan Comparison Using Ndiff .............................................................. 173

Ndiff Verbose Mode ............................................................................ 174

XML Output Mode .............................................................................. 175

Section 14: Tips and Tricks ................................................................ 177

Tips and Tricks Overview .................................................................... 178

Combine Multiple Options ................................................................. 179

Scan Using Interactive Mode .............................................................. 180

Runtime Interaction ........................................................................... 181

Remotely Scan Your Network ............................................................. 182

Wireshark ........................................................................................... 183

Scanme.Insecure.org .......................................................................... 184

Nmap Online Resources ..................................................................... 185

Appendix A - Nmap Cheat Sheet ....................................................... 187

Appendix B - Nmap Port States ......................................................... 191

Appendix C - CIDR Cross Reference ................................................... 193

Appendix D - Common TCP/IP Ports .................................................. 195

This guide is dedicated to the open source community. Without the tireless efforts

of open source developers, programs like Nmap would not exist. Many of these

developers devote large amounts of their spare time creating and supporting

wonderful open source applications and ask for nothing in return.

The collaborative manner in which open source software is developed shows the

true potential of humanity if we all work together towards a common goal.

Introduction

Nmap is an open source program released under the GNU General Public License

(see www.gnu.org/copyleft/gpl.html). It is an evaluable tool for network

administrators which can be used to discover, monitor, and troubleshoot TCP/IP

systems. Nmap is a free cross-platform network scanning utility created by Gordon

“Fyodor” Lyon and is actively developed by a community of volunteers.

A typical Nmap scan

Nmap’s award-winning suite of network scanning utilities has been in constant

development since 1997 and continually improves with each new release. Version

5.00 of Nmap (released in July of 2009) adds many new features and enhancements

including:

 Improved service and operating system version detection (see page 89)

 Improved support for Windows and Mac OS X

 Improved Nmap Scripting Engine (NSE) for performing complex scanning

tasks (see page 161)

 Addition of the Ndiff utility which can be used to compare Nmap scans (see

page 171)

 Ability to graphically display network topology with Zenmap (see page 147)

 Additional language localizations including German, French, and

Portuguese.

 Better overall performance

The Nmap project relies on volunteers to support and develop this amazing tool. If

you would like to help improve Nmap, there are several ways to get involved:

Promote Nmap

Nmap is a wonderful tool that every administrator network should know about.

Despite its popularity, Nmap isn’t widely known outside of technically elite circles.

Promote Nmap by introducing it to your friends or write a blog entry about it and

help spread the word.

Report Bugs

You can help improve Nmap by reporting any bugs you discover to the Nmap

developers. The Nmap project provides a mailing list for this which can be found

online at www.seclists.org/nmap-dev.

Note

Thousands of people worldwide use Nmap. Additionally, Nmap developers

are very busy people. Before reporting a bug, or asking for assistance, you

should search the Nmap website at www.insecure.org/search.html to

make sure your problem hasn’t already been reported or resolved.

Contribute Code

If you’re a hacker with some spare time on your hands, you can get involved with

Nmap development. To learn more about contributing code to the Nmap project

visit www.nmap.org/data/HACKING.

Submit TCP/IP Fingerprints

If you’re not a programmer, you can still improve Nmap by submitting any unknown

TCP/IP fingerprints you discover while scanning. The process for this is discussed on

page 92. Submitting fingerprints is easy and it helps improve Nmap’s software

version and operating system detection capabilities. Visit www.nmap.org/submit/

for more information or to submit your discoveries.

Sponsor Nmap

The Nmap project does not accept donations. If, however, you have a security

related service you would like promote, you can sponsor Nmap by purchasing an

advertising package on the insecure.org website. For more information visit

www.insecure.org/advertising.html.

Conventions Used In This Book

C:\>nmap scanme.insecure.org

Nmap running on Microsoft Windows systems

$ nmap scanme.insecure.org

Nmap running on non-privileged account for Unix/Linux/Mac OS X

# nmap scanme.insecure.org

Nmap running on Unix/Linux/Mac OS X systems as the root user

$ sudo nmap scanme.insecure.org

Using the sudo command to elevate privileges for Unix/Linux/Mac OS X

Note

Windows users may omit the sudo command where used in examples as

its use is not necessary and will not work on Microsoft based systems.

# nmap -T2 scanme.insecure.org

Using command line arguments with Nmap

Important

Nmap’s command line arguments are case sensitive. The -T2 option

(see page 100) in the example above is not the same as -t2 and will

result in an error if specified in the incorrect case.

...

Additional Nmap output truncated (to save space)

Section 1:

Installing Nmap

Installation Overview

Nmap has its roots in the Unix and Linux environment, but has recently become

more compatible with both Microsoft Windows and Apple’s Mac OS X operating

system. While great care is taken to make Nmap a universal experience on every

platform, the reality is that you may experience bugs, errors, and performance

issues when using Nmap on a non-traditional system. This applies mainly to

Windows and Mac OS X systems which have various idiosyncrasies that are not

present on a typical Unix or Linux system.

Author’s note: The Windows port of Nmap has greatly improved with Nmap 5.0.

Increases in performance and reliability make Nmap for Windows as reliable as its

Linux counterpart. Unfortunately, the Mac OS port is still a little rough around the

edges. Many of the problems with Nmap on Mac OS X stem from issues in Apple’s

latest release (Mac OS X 10.6). From monitoring the Nmap developers list, I can

confirm that developers are aware of these issues and working to resolve them.

These issues will no doubt be resolved over time as development of Nmap version

5.00 continues.

Skip ahead for installation procedures for your platform:

Installing Nmap on Windows

Page 21

Installing Nmap on Linux

Page 25

Installing Nmap from source (Unix and Linux)

Page 26

Installing Nmap on Mac OS X

Page 29

Installing Nmap on Windows

Step 1

Download the Windows version of Nmap from www.nmap.org.

Step 2

Launch the Nmap setup program. Select the default installation (recommended)

which will install the entire Nmap suite of utilities.

Nmap for Windows installer

Step 3

During installation, a helper program called WinPcap will also be installed. WinPcap

is required for Nmap to function properly on the Windows platform so do not skip

this step.

WinPcap for Windows installer

Step 4

After the WinPcap installation has completed you are given the option to configure

its service settings. The default options will enable the WinPcap service to start

when Windows boots. This is recommended as Nmap will not function correctly

when the WinPcap service is not running.

WinPcap settings

Step 5

Once Nmap has been successfully installed you can verify it is working correctly by

executing nmap scanme.insecure.org on the command line (located in Start >

Programs > Accessories > Command Prompt).

C:\>nmap scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-07 09:36 Central

Daylight Time

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 994 filtered ports

PORT STATE SERVICE

25/tcp closed smtp

70/tcp closed gopher

80/tcp open http

110/tcp closed pop3

113/tcp closed auth

31337/tcp closed Elite

Nmap done: 1 IP address (1 host up) scanned in 9.25 seconds

C:\>

Nmap test scan on Microsoft Windows

If the results of your scan are similar to the results above, then you have successfully

installed Nmap. If you receive an error, refer to Section 10 of this book for

troubleshooting and debugging information.

Installing Nmap on Unix and Linux systems

Most popular Linux distributions provide binary Nmap packages which allow for

simple installation. Installation on Unix systems requires compiling Nmap from

source code (as described on page 26).

Note

At the time of this writing Nmap version 5.00 was not available for

automatic installation on some Linux distributions. For many, installing

Nmap via the popular apt or yum package managers will only install

version 4.x. If your distribution already has Nmap 5.00 in their

repositories you can install Nmap by using the commands listed below.

Otherwise, refer to page 26 to install Nmap 5.00 from source code.

Installing Precompiled Packages for Linux

For Debian and Ubuntu based systems

# apt-get install nmap

For Red Hat and Fedora based systems

# yum install nmap

For Gentoo Linux based systems

# emerge nmap

To check which version of Nmap you are running, type the following command on

the command line:

# nmap -V

Nmap version 5.00 ( http://nmap.org )

Compiling Nmap from Source for Unix and Linux

Currently, the only way to get Nmap 5.00 for most Unix and Linux systems is to

download and compile the source code from the nmap.org website. Building Nmap

from source takes a little extra work, but is well worth the effort to get the new

features in Nmap’s latest release. The following five steps detail the procedure for

installing Nmap from source.

Step 1

Download the Nmap 5.00 source from www.nmap.org/download.html. This can be

done via a standard web browser or from the command line using the wget

command found on most Unix based systems.

$ wget http://nmap.org/dist/nmap-5.00.tgz

--2009-08-06 19:29:35-- http://nmap.org/dist/nmap-5.00.tgz

Resolving nmap.org... 64.13.134.48

Connecting to nmap.org|64.13.134.48|:80... connected.

HTTP request sent, awaiting response... 200 OK

Length: 9902346 (9.4M) [application/x-tar]

Saving to: `nmap-5.00.tgz'

100%[================================>] 9,902,346 1.39M/s in 7.5s

2009-08-06 19:29:42 (1.27 MB/s) - `nmap-5.00.tgz' saved

[9902346/9902346]

Downloading Nmap on Unix and Linux systems via the command line

Step 2

Extract the contents of the Nmap package by typing tar -xf nmap-5.00.tgz.

$ tar -xf nmap-5.00.tgz

...

Extracting Nmap source code

Step 3

Configure and build the Nmap source code by typing cd nmap-5.00/ and then

./configure && make on the command line.

$ cd nmap-5.00/

$ ./configure && make

checking build system type... x86_64-unknown-linux-gnu

checking host system type... x86_64-unknown-linux-gnu

checking for gcc... gcc

checking for C compiler default output file name... a.out

checking whether the C compiler works... yes

...

Compiling Nmap source code

Step 4

Install the compiled code by typing sudo make install on the command line.

Note

This step will require root privileges. You must login as the root user or

use the sudo command to complete this step.

$ sudo make install

Password: ********

/usr/bin/install -c -d /usr/local/bin /usr/local/share/man/man1

/usr/local/share/nmap

/usr/bin/install -c -c -m 755 nmap /usr/local/bin/nmap

/usr/bin/strip -x /usr/local/bin/nmap

/usr/bin/install -c -c -m 644 docs/nmap.1 /usr/local/share/man/man1/

/usr/bin/install -c -c -m 644 docs/nmap.xsl /usr/local/share/nmap/

...

NMAP SUCCESSFULLY INSTALLED

Installing Nmap from source code

Step 5

Once Nmap has been successfully installed, you can verify it is working correctly by

executing nmap localhost on the command line.

$ nmap localhost

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-07 00:42 CDT

Warning: Hostname localhost resolves to 2 IPs. Using 127.0.0.1.

Interesting ports on e6400 (127.0.0.1):

Not shown: 993 closed ports

PORT STATE SERVICE

22/tcp open ssh

25/tcp open smtp

111/tcp open rpcbind

139/tcp open netbios-ssn

445/tcp open microsoft-ds

631/tcp open ipp

2049/tcp open nfs

Nmap done: 1 IP address (1 host up) scanned in 0.20 seconds

Nmap test scan on Unix/Linux

If the results of your scan are similar to the results above, then you have successfully

installed Nmap. If you receive an error, refer to Section 10 of this book for

troubleshooting and debugging information.

Installing Nmap on Mac OS X

Step 1

Download the Mac OS X version of Nmap from www.nmap.org.

Note

Nmap 5.00 for Mac OS X is a universal installer that works on both Intel

and PowerPC Macintosh systems.

Step 2

Launch the Nmap setup program and click continue. Then, accept the license terms

of the Nmap program.

Nmap for Mac OS X installer

Step 3

When prompted for the installation options, leave the default selections checked

(recommended). This will install the entire Nmap suite of utilities. Click continue to

begin the installation process.

Default installation settings

Step 4

When the installation is complete you can close the Nmap installer.

Successful installation of Nmap on Mac OS X

Step 5

Once Nmap has been successfully installed, you can verify it is working correctly by

executing nmap localhost in the Mac OS X Terminal application (located in

Applications > Utilities > Terminal).

Nmap test scan on Mac OS X

If the results of your scan are similar to the results above, then you have successfully

installed Nmap. If you receive an error, refer to Section 10 of this book for

troubleshooting and debugging information.

Section 2:

Basic Scanning Techniques

Basic Scanning Overview

This section covers the basics of network scanning with Nmap. Before we begin it is

important to understand the following concepts:

 Firewalls, routers, proxy servers, and other security devices can skew the

results of an Nmap scan. Scanning remote hosts that are not on your local

network may provide misleading information because of this.

 Some scanning options require elevated privileges. On Unix and Linux

systems you may be required to login as the root user or to execute Nmap using

the sudo command.

There are also several warnings to take into consideration:

 Scanning networks that you do not have permission to scan can get you in

trouble with your internet service provider, the police, and possibly even the

government. Don’t go off scanning the FBI or Secret Service websites unless you

want to get in trouble.

 Aggressively scanning some systems may cause them to crash which can

lead to undesirable results like system downtime and data loss. Always scan

mission critical systems with caution.

Now let’s start scanning!

Scan a Single Target

Executing Nmap with no command line options will perform a basic scan on the

specified target. A target can be specified as an IP address or host name (which

Nmap will try to resolve).

Usage syntax: nmap [target]

$ nmap 192.168.10.1

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-07 19:38 CDT

Interesting ports on 192.168.10.1:

Not shown: 997 filtered ports

PORT STATE SERVICE

20/tcp closed ftp-data

21/tcp closed ftp

80/tcp open http

Nmap done: 1 IP address (1 host up) scanned in 7.21 seconds

Single target scan

The resulting scan shows the status of ports detected on the specified target. The

table below describes the output fields displayed by the scan.

PORT

STATE

SERVICE

Port number/protocol

Status of the port

Type of service for the port

A default Nmap scan will check for the 1000 most commonly used TCP/IP ports.

Ports that respond to a probe are classified into one of six port states: open, closed,

filtered, unfiltered, open|filtered, closed|filtered. See Appendix B for more

information about port states.

Scan Multiple Targets

Nmap can be used to scan multiple hosts at the same time. The easiest way to do

this is to string together the target IP addresses or host names on the command line

(separated by a space).

Usage syntax: nmap [target1 target2 etc]

$ nmap 192.168.10.1 192.168.10.100 192.168.10.101

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-07 20:30 CDT

Interesting ports on 192.168.10.1:

Not shown: 997 filtered ports

PORT STATE SERVICE

20/tcp closed ftp-data

21/tcp closed ftp

80/tcp open http

Interesting ports on 192.168.10.100:

Not shown: 995 closed ports

PORT STATE SERVICE

22/tcp open ssh

111/tcp open rpcbind

139/tcp open netbios-ssn

445/tcp open microsoft-ds

2049/tcp open nfs

Nmap done: 3 IP addresses (2 hosts up) scanned in 6.23 seconds

Multiple target scan

The example above demonstrates using Nmap to scan three addresses at the same

time.

Tip

Since all three targets in the above example are on the same subnet you

could use the shorthand notation of nmap 192.168.10.1,100,101 to

achieve the same results.

Scan a Range of IP Addresses

A range of IP addresses can be used for target specification as demonstrated in the

example below.

Usage syntax: nmap [Range of IP addresses]

$ nmap 192.168.10.1-100

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-07 20:40 CDT

Interesting ports on 192.168.10.1:

Not shown: 997 filtered ports

PORT STATE SERVICE

20/tcp closed ftp-data

21/tcp closed ftp

80/tcp open http

Interesting ports on 192.168.10.100:

Not shown: 995 closed ports

PORT STATE SERVICE

22/tcp open ssh

111/tcp open rpcbind

139/tcp open netbios-ssn

445/tcp open microsoft-ds

Nmap done: 100 IP addresses (2 hosts up) scanned in 25.84 seconds

Scanning a range of IP addresses

In this example Nmap is instructed to scan the range of IP addresses from

192.168.10.1 through 192.168.10.100. You can also use ranges to scan multiple

networks/subnets. For example typing nmap 192.168.1-100.* would scan the class

C IP networks of 192.168.1.* through 192.168.100.*.

Note

The asterisk is a wildcard character which represents all valid ranges from

0-255.

Scan an Entire Subnet

Nmap can be used to scan an entire subnet using CIDR (Classless Inter-Domain

Routing) notation.

Usage syntax: nmap [Network/CIDR]

$ nmap 192.168.10.1/24

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-07 20:43 CDT

Interesting ports on 192.168.10.1:

Not shown: 996 filtered ports

PORT STATE SERVICE

20/tcp closed ftp-data

21/tcp closed ftp

23/tcp closed telnet

80/tcp open http

Interesting ports on 192.168.10.100:

Not shown: 995 closed ports

PORT STATE SERVICE

22/tcp open ssh

111/tcp open rpcbind

139/tcp open netbios-ssn

445/tcp open microsoft-ds

2049/tcp open nfs

Nmap done: 256 IP addresses (2 hosts up) scanned in 8.78 second

Scanning an entire class C subnet using CDIR notation

The above example instructs Nmap to scan the entire 192.168.10.0 network using

CIDR notation. CIDR notation consists of the network address and subnet mask (in

binary bits) separated by a slash. See Appendix C for a cross reference of subnet

masks and their CIDR notations.

Scan a List of Targets

If you have a large number of systems to scan, you can enter the IP address (or host

names) in a text file and use that file as input for Nmap on the command line.

$ cat list.txt

192.168.10.1

192.168.10.100

192.168.10.101

Target IP addresses in a text file

The list.txt file above contains a list of hosts to be scanned. Each entry in the list.txt

file must be separated by a space, tab, or newline. The -iL parameter is used to

instruct Nmap to extract the list of targets from the list.txt file.

Usage syntax: nmap -iL [list.txt]

$ nmap -iL list.txt

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-07 19:44 CDT

Interesting ports on 192.168.10.1:

Not shown: 997 filtered ports

PORT STATE SERVICE

20/tcp closed ftp-data

21/tcp closed ftp

80/tcp open http

Interesting ports on 192.168.10.100:

Not shown: 995 closed ports

PORT STATE SERVICE

22/tcp open ssh

...

Nmap scan using a list for target specification

The resulting scan displayed above will be performed for each host in the list.txt file.

Scan Random Targets

The -iR parameter can be used to select random internet hosts to scan. Nmap will

randomly generate the specified number of targets and attempt to scan them.

Usage syntax: nmap -iR [number of targets]

# nmap -iR 3

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-07 23:40 CDT

...

Nmap done: 3 IP addresses (2 hosts up) scanned in 36.91 seconds

Scanning three randomly generated IP addresses

Note

For privacy reasons we do not display the results of the above scan in this

book.

Executing nmap -iR 3 instructs Nmap to randomly generate 3 IP addresses to scan.

There aren’t many good reasons to ever do a random scan unless you are working

on a research project (or just really bored). Additionally, if you do a lot of aggressive

random scanning you could end up getting in trouble with your internet service

provider.

Exclude Targets from a Scan

The --exclude option is used with Nmap to exclude hosts from a scan.

Usage syntax: nmap [targets] --exclude [target(s)]

$ nmap 192.168.10.0/24 --exclude 192.168.10.100

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-08 20:39 CDT

Interesting ports on 192.168.10.1:

Not shown: 996 filtered ports

PORT STATE SERVICE

20/tcp closed ftp-data

21/tcp closed ftp

23/tcp closed telnet

80/tcp open http

...

Excluding a single IP from a scan

The --exclude option is useful if you want to exclude specific hosts when scanning a

large number of addresses. In the example above host 192.168.10.100 is excluded

from the range of targets being scanned.

The --exclude option accepts single hosts, ranges, or entire network blocks (using

CIDR notation) as demonstrated in the next example.

$ nmap 192.168.10.0/24 --exclude 192.168.10.100-105

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-08 20:39 CDT

...

Excluding a range of IP addresses from a scan

Exclude Targets Using a List

The --excludefile option is similar to the --exclude option and can be used to

provide a list of targets to exclude from a network scan.

$ cat list.txt

192.168.10.1

192.168.10.12

192.168.10.44

Text file with hosts to exclude from a scan

The example below demonstrates using the --excludefile argument to exclude the

hosts in the list.txt file displayed above.

Usage syntax: nmap [targets] --excludefile [list.txt]

$ nmap 192.168.10.0/24 --excludefile list.txt

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-08 20:49 CDT

Interesting ports on 192.168.10.100:

Not shown: 995 closed ports

PORT STATE SERVICE

22/tcp open ssh

111/tcp open rpcbind

139/tcp open netbios-ssn

445/tcp open microsoft-ds

2049/tcp open nfs

Nmap done: 253 IP addresses (1 host up) scanned in 33.10 second

Excluding a list of hosts from a network scan

In the above example, the targets in the list.txt file are excluded from the scan.

Perform an Aggressive Scan

The -A parameter instructs Nmap to perform an aggressive scan.

Usage syntax: nmap -A [target]

# nmap -A 10.10.1.51

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-10 09:39 CDT

Interesting ports on 10.10.1.51:

Not shown: 999 closed ports

PORT STATE SERVICE VERSION

80/tcp open http Linksys WAP54G wireless-G router http config

|_ html-title: 401 Unauthorized

| http-auth: HTTP Service requires authentication

|_ Auth type: Basic, realm = Linksys WAP54G

MAC Address: 00:12:17:AA:66:28 (Cisco-Linksys)

Device type: general purpose

Running: Linux 2.4.X

OS details: Linux 2.4.18 - 2.4.35 (likely embedded)

Network Distance: 1 hop

Service Info: Device: WAP

OS and Service detection performed. Please report any incorrect

results at http://nmap.org/submit/ .

Nmap done: 1 IP address (1 host up) scanned in 9.61 seconds

Output of an aggressive scan

The aggressive scan selects some of the most commonly used options within Nmap

and is provided as a simple alternative to typing a long string of command line

arguments. The -A parameter is a synonym for several advanced options (like -O -sC

--traceroute) which can also be accessed individually and are covered later in this

book.

Scan an IPv6 Target

The -6 parameter is used to perform a scan of an IP version 6 target.

Usage syntax: nmap -6 [target]

# nmap -6 fe80::29aa:9db9:4164:d80e

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-11 15:52 Central

Daylight Time

Interesting ports on fe80::29aa:9db9:4164:d80e:

Not shown: 993 closed ports

PORT STATE SERVICE

135/tcp open msrpc

445/tcp open microsoft-ds

5357/tcp open unknown

49152/tcp open unknown

49153/tcp open unknown

49154/tcp open unknown

49155/tcp open unknown

Nmap done: 1 IP address (1 host up) scanned in 227.32 seconds

Scanning an IPv6 address

The example above displays the results of scanning an IP version 6 target. Most

Nmap options support IPv6 with the exception of multiple target scanning using

ranges and CIDR as they are pointless on IPv6 networks.

Note

Both the host and the target systems must support the IPv6 protocol in

order for a -6 scan to work.

Section 3:

Discovery Options

Discovery Options Overview

Before port scanning a target, Nmap will attempt to send ICMP echo requests to see

if the host is “alive.” This can save time when scanning multiple hosts as Nmap will

not waste time attempting to probe hosts that are not online. Because ICMP

requests are often blocked by firewalls, Nmap will also attempt to connect to port

80 and 443 since these common web server ports are often open (even if ICMP is

not).

The default discovery options aren’t useful when scanning secured systems and can

hinder scanning progress. The following section describes alternative methods for

host discovery which allows you to perform more comprehensive discovery when

looking for available targets.

Summary of features covered in this section:

Feature

Option

Don’t Ping

-PN

Perform a Ping Only Scan

-sP

TCP SYN Ping

-PS

TCP ACK Ping

-PA

UDP Ping

-PU

SCTP INIT Ping

-PY

ICMP Echo Ping

-PE

ICMP Timestamp Ping

-PP

ICMP Address Mask Ping

-PM

IP Protocol Ping

-PO

ARP Ping

-PR

Traceroute

--traceroute

Force Reverse DNS Resolution

-R

Disable Reverse DNS Resolution

-n

Alternative DNS Lookup

--system-dns

Manually Specify DNS Server(s)

--dns-servers

Create a Host List

-sL

Don’t Ping

By default, before Nmap attempts to scan a system for open ports it will first ping

the target to see if it is online. This feature helps save time when scanning as it

causes targets that do not respond to be skipped.

$ nmap 10.10.5.11

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 08:43 CDT

Note: Host seems down. If it is really up, but blocking our ping

probes, try -PN

Nmap done: 1 IP address (0 hosts up) scanned in 3.16 seconds

Results of a Nmap scan where the target system is not pingable

In the above example the specified target is not scanned as it does not respond to

Nmap’s pings. The -PN option instructs Nmap to skip the default discovery check

and perform a complete port scan on the target. This is useful when scanning hosts

that are protected by a firewall that blocks ping probes.

Usage syntax: nmap -PN [target]

$ nmap -PN 10.10.5.11

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 08:43 CDT

Interesting ports on 10.10.5.11:

Not shown: 999 filtered ports

PORT STATE SERVICE

3389/tcp open ms-term-serv

Nmap done: 1 IP address (1 host up) scanned in 6.51 seconds

Output of a Nmap scan with ping discovery disabled

By specifying the -PN option on the same target, Nmap is able to produce a list of

open ports on the unpingable system.

Ping Only Scan

The -sP option is used to perform a simple ping of the specified host.

Usage syntax: nmap -sP [target]

$ nmap -sP 192.168.10.2/24

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-08 20:54 CDT

Host 192.168.10.1 is up (0.0026s latency).

Host 192.168.10.100 is up (0.00020s latency).

Host 192.168.10.101 is up (0.00026s latency).

Nmap done: 256 IP addresses (3 hosts up) scanned in 3.18 second

Output of a ping only scan

This option is useful when you want to perform a quick search of the target network

to see which hosts are online without actually scanning the target(s) for open ports.

In the above example, all 254 addresses in the 192.168.10.0 subnet are pinged and

results from live hosts are displayed.

When scanning a local network, you can execute Nmap with root privileges for

additional ping functionality. When doing this, the -sP option will perform an ARP

ping and return the MAC addresses of the discovered system(s).

Usage syntax: nmap -sP [target]

# nmap -sP 192.168.10.2/24

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-08 21:00 CDT

Host 192.168.10.1 is up (0.0037s latency).

MAC Address: 00:16:B6:BE:6D:1D (Cisco-Linksys)

...

Output of a ping only scan (as root)

TCP SYN Ping

The -PS option performs a TCP SYN ping.

Usage syntax: nmap -PS[port1,port1,etc] [target]

# nmap -PS scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-16 13:31 CDT

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 995 filtered ports

PORT STATE SERVICE

53/tcp open domain

70/tcp closed gopher

80/tcp open http

113/tcp closed auth

31337/tcp closed Elite

Nmap done: 1 IP address (1 host up) scanned in 27.41 seconds

Performing a TCP SYN ping

The TCP SYN ping sends a SYN packet to the target system and listens for a response.

This alternative discovery method is useful for systems that are configured to block

standard ICMP pings.

Note

The default port for -PS is 80, but others can be specified using the

following syntax: nmap -PS22,25,80,443,etc.

TCP ACK Ping

The -PA performs a TCP ACK ping on the specified target.

Usage syntax: nmap -PA[port1,port1,etc] [target]

# nmap -PA 192.168.1.254

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-16 13:31 CDT

Interesting ports on home (192.168.1.254):

Not shown: 998 closed ports

PORT STATE SERVICE

80/tcp open http

443/tcp open https

MAC Address: 00:25:3C:5F:5A:89 (2Wire)

Nmap done: 1 IP address (1 host up) scanned in 0.81 seconds

Performing a TCP ACK ping

The -PA option causes Nmap to send TCP ACK packets to the specified hosts. This

method attempts to discover hosts by responding to TCP connections that are

nonexistent in an attempt to solicit a response from the target. Like other ping

options, it is useful in situations where standard ICMP pings are blocked.

Note

The default port for -PA is 80, but others can be specified using the

following syntax: nmap -PA22,25,80,443,etc.

UDP Ping

The -PU option performs a UDP ping on the target system.

Usage syntax: nmap -PU[port1,port1,etc] [target]

# nmap -PU 192.168.1.254

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-16 13:30 CDT

Interesting ports on home (192.168.1.254):

Not shown: 998 closed ports

PORT STATE SERVICE

80/tcp open http

443/tcp open https

MAC Address: 00:25:3C:5F:5A:89 (2Wire)

Nmap done: 1 IP address (1 host up) scanned in 0.81 second

Performing a UDP ping

This discovery method sends UPD packets in an attempt to solicit a response from a

target. While most firewalled systems will block this type of connection, some

poorly configured systems may allow it if they are only configured to filter TCP

connections.

Note

The default port for -PU is 40125. Others can be specified by using the

following syntax: nmap -PU22,25,80,443,etc.

SCTP INIT Ping

The -PY parameter instructs Nmap to perform an SCTP INIT ping.

Usage syntax: nmap -PY[port1,port1,etc] [target]

# nmap -PY 192.168.1.254

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-16 13:28 CDT

Interesting ports on home (192.168.1.254):

Not shown: 998 closed ports

PORT STATE SERVICE

80/tcp open http

443/tcp open https

MAC Address: 00:25:3C:5F:5A:89 (2Wire)

Nmap done: 1 IP address (1 host up) scanned in 0.79 seconds

Performing a SCTP INIT ping

This discovery method attempts to locate hosts using the Stream Control

Transmission Protocol (SCTP). SCTP is typically used on systems for IP based

telephony.

Note

The default port for -PY is 80. Others can be specified by using the

following syntax: nmap -PY22,25,80,443,etc.

ICMP Echo Ping

The -PE option performs an ICMP (Internet Control Message Protocol) echo ping on

the specified system.

Usage syntax: nmap -PE [target]

# nmap -PE 192.168.1.254

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-16 13:26 CDT

Interesting ports on home (192.168.1.254):

Not shown: 998 closed ports

PORT STATE SERVICE

80/tcp open http

443/tcp open https

MAC Address: 00:25:3C:5F:5A:89 (2Wire)

Nmap done: 1 IP address (1 host up) scanned in 1.89 seconds

Performing an ICMP echo ping

The -PE option sends a standard ICMP ping to the target to see if it replies. This type

of discovery works best on local networks where ICMP packets can be transmitted

with few restrictions. Many internet hosts, however, are configured not respond to

ICMP packets for security reasons.

Note

The -PE option is automatically implied if no other ping options are

specified.

ICMP Timestamp Ping

The -PP option performs an ICMP timestamp ping.

Usage syntax: nmap -PP [target]

# nmap -PP 192.168.1.254

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-16 13:27 CDT

Interesting ports on home (192.168.1.254):

Not shown: 998 closed ports

PORT STATE SERVICE

80/tcp open http

443/tcp open https

MAC Address: 00:25:3C:5F:5A:89 (2Wire)

Nmap done: 1 IP address (1 host up) scanned in 1.83 seconds

Performing an ICMP timestamp ping

While most firewalled systems are configured to block ICMP echo requests, some

improperly configured systems may still reply to ICMP timestamp requests. This

makes -PP useful for attempting to solicit responses from firewalled targets.

ICMP Address Mask Ping

The -PM option performs an ICMP address mask ping.

Usage syntax: nmap -PM [target]

# nmap -PM 192.168.1.254

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-16 13:26 CDT

Interesting ports on home (192.168.1.254):

Not shown: 998 closed ports

PORT STATE SERVICE

80/tcp open http

443/tcp open https

MAC Address: 00:25:3C:5F:5A:89 (2Wire)

Nmap done: 1 IP address (1 host up) scanned in 1.92 seconds

Performing an ICMP address mask ping

This unconventional ICMP query (similar to the -PP option) attempts to ping the

specified host using alternative ICMP registers. This type of ping can occasionally

sneak past a firewall that is configured to block standard echo requests.

IP Protocol Ping

The -PO option performs an IP protocol ping.

Usage syntax: nmap -PO[protocol1,protocol2,etc] [target]

# nmap -PO 10.10.1.48

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-17 09:38 CDT

Interesting ports on 10.10.1.48:

Not shown: 994 closed ports

PORT STATE SERVICE

21/tcp open ftp

22/tcp open ssh

25/tcp open smtp

80/tcp open http

111/tcp open rpcbind

2049/tcp open nfs

MAC Address: 00:0C:29:D5:38:F4 (VMware)

Nmap done: 1 IP address (1 host up) scanned in 1.97 seconds

Performing an IP protocol ping

An IP protocol ping sends packets with the specified protocol to the target. If no

protocols are specified the default protocols 1 (ICMP), 2 (IGMP), and 4 (IP-in-IP) are

used. To ping using a custom set of protocols, use the following syntax:

nmap -PO1,2,4,etc.

Note

A complete list of Internet Protocol numbers can be found online at

www.iana.org/assignments/protocol-numbers/

ARP Ping

The -PR option instructs Nmap to perform an ARP (Address Resolution Protocol)

ping on the specified target.

Usage syntax: nmap -PR [target]

# nmap -PR 192.168.1.254

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-16 13:16 CDT

Interesting ports on 192.168.1.254:

Not shown: 998 closed ports

PORT STATE SERVICE

80/tcp open http

443/tcp open https

MAC Address: 00:25:3C:5F:5A:89 (2Wire)

Nmap done: 1 IP address (1 host up) scanned in 0.81 seconds

Performing an ARP ping

The -PR option is automatically implied when scanning the local network. This type

of discovery is much faster than the other ping methods described in this guide. It

also has the added benefit of being more accurate because LAN hosts can’t block

ARP requests (even if they are behind a firewall).

Note

APR scans cannot be performed on targets that are not on your local

subnet.

Traceroute

The --traceroute parameter can be use to trace the network path to the specified

host.

Usage syntax: nmap --traceroute [target]

# nmap --traceroute scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-16 13:01 CDT

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 996 filtered ports

PORT STATE SERVICE

53/tcp open domain

70/tcp closed gopher

80/tcp open http

113/tcp closed auth

TRACEROUTE (using port 113/tcp)

HOP RTT ADDRESS

1 0.91 home (192.168.1.254)

2 24.40 99-60-32-2.lightspeed.wchtks.sbcglobal.net (99.60.32.2)

3 23.12 76.196.172.4

4 22.69 151.164.94.52

5 32.79 ex3-p12-0.eqdltx.sbcglobal.net (69.220.8.53)

6 32.74 asn2828-XO.eqdltx.sbcglobal.net (151.164.249.134)

...

13 74.90 ip65-46-255-94.z255-46-65.customer.algx.net (65.46.255.94)

14 75.01 scanme.nmap.org (64.13.134.52)

Nmap done: 1 IP address (1 host up) scanned in 33.72 seconds

Output of a traceroute scan

The information displayed is similar to the traceroute or tracepath commands

found on Unix and Linux systems - with the added bonus of Nmap’s tracing being

functionally superior to these commands.

Force Reverse DNS Resolution

The -R parameter instructs Nmap to always perform reverse DNS resolution on the

target IP address.

Usage syntax: nmap -R [target]

# nmap -R 64.13.134.52

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 17:22 Central

Daylight Time

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 993 filtered ports

PORT STATE SERVICE

25/tcp closed smtp

53/tcp open domain

70/tcp closed gopher

80/tcp open http

110/tcp closed pop3

113/tcp closed auth

31337/tcp closed Elite

Nmap done: 1 IP address (1 host up) scanned in 9.38 seconds

Output of a Nmap scan with reverse DNS enabled

By default, Nmap will only do reverse DNS for hosts that appear to be online. The -R

option is useful when performing reconnaissance on a block of IP addresses as

Nmap will try to resolve the reverse DNS information of every IP address. The

reverse DNS information can reveal interesting information about the target IP

address (even if it is offline or blocking Nmap’s probes).

Note

The -R option can dramatically reduce the performance of a scan.

Disable Reverse DNS Resolution

The -n parameter is used to disable reverse DNS lookups.

Usage syntax: nmap -n [target]

# nmap -n 64.13.134.52

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 17:23 Central

Daylight Time

Interesting ports on 64.13.134.52:

Not shown: 993 filtered ports

PORT STATE SERVICE

25/tcp closed smtp

53/tcp open domain

70/tcp closed gopher

80/tcp open http

110/tcp closed pop3

113/tcp closed auth

31337/tcp closed Elite

Nmap done: 1 IP address (1 host up) scanned in 8.48 seconds

Output of a Nmap scan with reverse DNS disabled

Reverse DNS dramatically can significantly slow an Nmap scan. Using the -n option

greatly reduces scanning times - especially when scanning a large number of hosts.

This option is useful if you don’t care about the DNS information for the target

system and prefer to perform a scan which produces faster results.

Alternative DNS Lookup Method

The --system-dns option instructs Nmap to use the host system’s DNS resolver

instead of its own internal method.

Usage syntax: nmap --system-dns [target]

$ nmap --system-dns scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-09 21:47 CDT

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 972 closed ports, 26 filtered ports

PORT STATE SERVICE

53/tcp open domain

80/tcp open http

Nmap done: 1 IP address (1 host up) scanned in 19.86 second

Output of a Nmap scan using the system DNS resolver

This option is rarely used as it is much slower than the default method. It can,

however, be useful when troubleshooting DNS problems with Nmap.

Note

The system resolver is always used for IPv6 scans as Nmap has not yet

fully implemented its own internal IPv6 resolver.

Manually Specify DNS Server(s)

The --dns-servers option is used to manually specify DNS servers to be queried

when scanning.

Usage syntax: nmap --dns-servers [server1,server2,etc] [target]

$ nmap --dns-servers 208.67.222.222,208.67.220.220 scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-09 22:40 CDT

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 998 closed ports

PORT STATE SERVICE

53/tcp open domain

80/tcp open http

Nmap done: 1 IP address (1 host up) scanned in 32.07 seconds

Manually specifying DNS servers

Nmap’s default behavior will use the DNS servers configured on your local system

for name resolution. The --dns-servers option allows you to specify one or more

alternative servers for Nmap to query. This can be useful for systems that do not

have DNS configured or if you want to prevent your scan lookups from appearing in

your locally configured DNS server’s log file.

Note

This option is currently not available for IPv6 scans.

Create a Host List

The -sL option will display a list and performs a reverse DNS lookup of the specified

IP addresses.

Usage syntax: nmap -sL [target]

$ nmap -sL 10.10.1.1/24

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-14 13:56 CDT

Host 10.10.1.0 not scanned

Host router.nmapcookbook.com (10.10.1.1) not scanned

Host server.nmapcookbook.com (10.10.1.2) not scanned

Host 10.10.1.3 not scanned

Host 10.10.1.4 not scanned

Host mylaptop.nmapcookbook.com (10.10.1.5) not scanned

Host 10.10.1.6 not scanned

Host 10.10.1.7 not scanned

Host 10.10.1.8 not scanned

Host mydesktop.nmapcookbook.com (10.10.1.9) not scanned

Host mydesktop2.nmapcookbook.com (10.10.1.10) not scanned

Host 10.10.1.11 not scanned

Host 10.10.1.12 not scanned

Host 10.10.1.13 not scanned

Host 10.10.1.14 not scanned

Host 10.10.1.15 not scanned

Host 10.10.1.16 not scanned

Host 10.10.1.17 not scanned

...

Output of a host list generated by Nmap

The above scan shows the results of the DNS names for the specified systems. This

scan is useful for identifying the IP addresses and DNS names for the specified

targets without sending any packets to them. Many DNS names can reveal

interesting information about an IP address including what it used for or where it is

located.

Section 4:

Advanced Scanning Options

Advanced Scanning Functions Overview

Nmap supports a number of user selectable scan types. By default, Nmap will

perform a basic TCP scan on each target system. In some situations, it may be

necessary to perform more complex TCP (or even UDP) scans in an attempt to find

uncommon services or to evade a firewall. These advanced scan types are covered

in this section.

Summary of features covered in this section:

Feature

Option

TCP SYN Scan

-sS

TCP Connect Scan

-sT

UDP Scan

-sU

TCP NULL Scan

-sN

TCP FIN Scan

-sF

Xmas Scan

-sX

TCP ACK Scan

-sA

Custom TCP Scan

--scanflags

IP Protocol Scan

-sO

Send Raw Ethernet Packets

--send-eth

Send IP Packets

--send-ip

Note

You must login with root/administrator privileges (or use the sudo

command) to execute many of the scans discussed in this section.

TCP SYN Scan

The -sS option performs a TCP SYN scan.

Usage syntax: nmap -sS [target]

# nmap -sS 10.10.1.48

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-25 11:01 CDT

Interesting ports on 10.10.1.48:

Not shown: 994 closed ports

PORT STATE SERVICE

21/tcp open ftp

22/tcp open ssh

25/tcp open smtp

80/tcp open http

111/tcp open rpcbind

2049/tcp open nfs

MAC Address: 00:0C:29:D5:38:F4 (VMware)

Nmap done: 1 IP address (1 host up) scanned in 1.73 seconds

Performing a TCP SYN scan

The TCP SYN scan is the default option for privileged users (users running as root on

Unix/Linux or Administrator on Windows). The default TCP SYN scan attempts to

identify the 1000 most commonly used TCP ports by sending a SYN packet to the

target and listening for a response. This type of scan is said to be stealthy because it

does not attempt to open a full-fledged connection to the remote host. This

prevents many systems from logging a connection attempt from your scan.

Note

Stealth operation is not guaranteed. Modern packet capture programs

and advanced firewalls are now able to detect TCP SYN scans.

TCP Connect Scan

The -sT option performs a TCP connect scan.

Usage syntax: nmap -sT [target]

$ nmap -sT 10.10.1.1

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-31 13:06 CDT

Interesting ports on 10.10.1.1:

Not shown: 998 closed ports

PORT STATE SERVICE

80/tcp open http

443/tcp open https

Nmap done: 1 IP address (1 host up) scanned in 0.56 seconds

Performing a TCP connect scan

The -sT scan is the default scan type for non-privileged users. It is also used when

scanning IPv6 targets. The TCP Connect Scan is a simple probe that attempts to

directly connect to the remote system without using any stealth (as described on

page 67).

Tip

It is typically best to execute Nmap with root privileges whenever possible

as it will perform a TCP SYN scan (-sS) which can provide a more accurate

listing of port states and is significantly faster.

UDP Scan

The -sU option performs a UDP (User Datagram Protocol) scan.

Usage syntax: nmap -sU [target]

# nmap -sU 10.10.1.41

Starting Nmap 5.00 ( http://nmap.org ) at 2009-09-06 21:20 CDT

Interesting ports on 10.10.1.41:

Not shown: 984 closed ports

PORT STATE SERVICE

7/udp open echo

9/udp open|filtered discard

13/udp open daytime

19/udp open chargen

37/udp open time

69/udp open|filtered tftp

111/udp open|filtered rpcbind

137/udp open|filtered netbios-ns

138/udp open|filtered netbios-dgm

177/udp open|filtered xdmcp

514/udp open|filtered syslog

518/udp open|filtered ntalk

1028/udp open|filtered ms-lsa

1030/udp open|filtered iad1

2049/udp open|filtered nfs

MAC Address: 00:60:B0:59:B6:14 (Hewlett-packard CO.)

Nmap done: 1 IP address (1 host up) scanned in 1.91 seconds

Performing a UDP scan

The example above displays the results of a UDP scan. While TCP is the most

commonly used protocol, many network services (like DNS, DHCP, and SNMP) still

utilize UDP. When performing a network audit, it’s always a good idea to check for

both TCP and UDP services to get a more complete picture of the target

host/network.

TCP NULL Scan

The -sN option performs a TCP NULL scan.

Usage syntax: nmap -sN [target]

# nmap -sN 10.10.1.48

Starting Nmap 5.00 ( http://nmap.org ) at 2009-10-01 13:19 CDT

Interesting ports on 10.10.1.48:

Not shown: 994 closed ports

PORT STATE SERVICE

21/tcp open|filtered ftp

22/tcp open|filtered ssh

25/tcp open|filtered smtp

80/tcp open|filtered http

111/tcp open|filtered rpcbind

2049/tcp open|filtered nfs

MAC Address: 00:0C:29:D5:38:F4 (VMware)

Nmap done: 1 IP address (1 host up) scanned in 1.54 seconds

Performing a TCP NULL scan

A TCP NULL scan causes Nmap to send packets with no TCP flags enabled. This is

done by setting the packet header to 0. Sending NULL packets to a target is a

method of tricking a firewalled system to generate a response.

Note

Not all systems will respond to probes of this type.

See also: --send-eth (page 76)

Section 5:

Port Scanning Options

Port Scanning Options Overview

There are a total of 131,070 TCP/IP ports (65,535 TCP and 65,535 UDP). Nmap, by

default, only scans 1,000 of the most commonly used ports. This is done to save

time when scanning multiple targets as the majority of ports outside the top 1000

are rarely used. Sometimes, however, you may want to scan outside the default

range of ports to look for uncommon services or ports that have been forwarded to

a different location. This section covers the options which allow this and other port

specific features.

Tip

A complete list of TCP/IP ports can be found on the IANA website at

www.iana.org/assignments/port-numbers.

Summary of features covered in this section:

Feature

Option

Perform a Fast Scan

-F

Scan Specific Ports

-p [port]

Scan Ports by Name

-p [name]

Scan Ports by Protocol

-p U:[UDP ports],T:[TCP ports]

Scan All Ports

-p “*”

Scan Top Ports

--top-ports [number]

Perform a Sequential Port Scan

-r

Perform a Fast Scan

The -F option instructs Nmap to perform a scan of only the 100 most commonly

used ports.

Usage syntax: nmap -F [target]

$ nmap -F 10.10.1.44

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 10:13 CDT

Interesting ports on 10.10.1.44:

Not shown: 91 closed ports

PORT STATE SERVICE

25/tcp open smtp

53/tcp open domain

80/tcp open http

135/tcp open msrpc

139/tcp open netbios-ssn

445/tcp open microsoft-ds

3389/tcp open ms-term-serv

8000/tcp open http-alt

10000/tcp open snet-sensor-mgmt

Nmap done: 1 IP address (1 host up) scanned in 2.43 seconds

Output of a “fast” scan

Nmap scans the top 1000 commonly used ports by default. The -F option reduces

that number to 100. This can dramatically speed up scanning while still representing

the majority of commonly used ports.

Scan Specific Ports

The -p option is used to instruct Nmap to scan the specified port(s).

Usage syntax: nmap -p [port] [target]

$ nmap -p 80 10.10.1.44

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 10:10 CDT

Interesting ports on 10.10.1.44:

PORT STATE SERVICE

80/tcp open http

Nmap done: 1 IP address (1 host up) scanned in 0.12 seconds

Specifying a single port to scan

The example above demonstrates using -p to scan port 80. In addition to scanning a

single port, you can scan multiple individual ports (separated by a comma) or a

range of ports as demonstrated in the next example.

Usage syntax: nmap [port1,port2,etc|range of ports] [target]

$ nmap -p 25,53,80-200 10.10.1.44

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 10:10 CDT

Interesting ports on 10.10.1.44:

Not shown: 118 closed ports

PORT STATE SERVICE

25/tcp open smtp

53/tcp open domain

80/tcp open http

135/tcp open msrpc

139/tcp open netbios-ssn

Nmap done: 1 IP address (1 host up) scanned in 0.15 seconds

Specifying multiple ports to scan

In this example the -p option is used to scan ports 25, 53, and 80 through 200.

Scan Ports by Name

The -p option can be used to scan ports by name.

Usage syntax: nmap -p [port name(s)] [target]

$ nmap -p smtp,http 10.10.1.44

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-17 10:37 CDT

Interesting ports on 10.10.1.44:

PORT STATE SERVICE

25/tcp open smtp

80/tcp open http

8008/tcp closed http

Nmap done: 1 IP address (1 host up) scanned in 0.10 seconds

Scanning ports by name

The example above demonstrates searching for open SMTP and HTTP ports by name

using the -p option. The name(s) specified must match a service in the

nmap-services file. This is usually found in /usr/local/share/nmap/ on Unix/Linux

systems or C:\Program Files\Nmap\ on Windows systems.

Wildcards can also be used when specifying services by name. For example,

executing nmap -p "http*" 10.10.1.44 would scan for all ports that start with http

(including http and https).

Note

You must enclose the wildcard statement in quotes so your system does

not interpret it as a shell wildcard.

Scan Ports by Protocol

Specifying a T: or U: prefix with the -p option allows you to search for a specific port

and protocol combination.

Usage syntax: nmap -p U:[UDP ports],T:[TCP ports] [target]

# nmap -sU -sT -p U:53,T:25 10.10.1.44

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-18 12:52 CDT

Interesting ports on 10.10.1.44:

PORT STATE SERVICE

25/tcp open smtp

53/udp open domain

MAC Address: 00:14:22:0F:3C:0E (Dell)

Nmap done: 1 IP address (1 host up) scanned in 0.19 seconds

Scanning specific ports by protocol

Using the syntax -p U:53,T:25 instructs Nmap to perform a UDP scan on port 53 and

a TCP scan on port 25.

Note

Nmap, by default, will only scan TCP ports. In order to scan both TCP and

UDP ports you will need to enable additional scan types such as

-sU and -sT which are covered in Section 4 of this book.

Scan All Ports

The -p "*" option is a wildcard used to scan all 65,535 TCP/IP ports on the specified

target.

Usage syntax: nmap -p “*” [target]

# nmap -p "*" 10.10.1.41

Starting Nmap 5.00 ( http://nmap.org ) at 2009-12-16 14:07 Central

Standard Time

Interesting ports on 10.10.1.41:

Not shown: 4204 closed ports

PORT STATE SERVICE

7/tcp open echo

9/tcp open discard

13/tcp open daytime

19/tcp open chargen

21/tcp open ftp

23/tcp open telnet

25/tcp open smtp

37/tcp open time

111/tcp open rpcbind

113/tcp open auth

139/tcp open netbios-ssn

512/tcp open exec

513/tcp open login

514/tcp open shell

515/tcp open printer

543/tcp open klogin

...

Scanning all ports on a target system

Note

You must enclose the wildcard statement in quotes so your system does

not interpret it as a shell wildcard.

Scan Top Ports

The --top-ports option is used to scan the specified number of top ranked ports.

Usage syntax: nmap --top-ports [number] [target]

# nmap --top-ports 10 10.10.1.41

Starting Nmap 5.00 ( http://nmap.org ) at 2009-12-15 13:46 CST

Interesting ports on 10.10.1.41:

PORT STATE SERVICE

21/tcp open ftp

22/tcp closed ssh

23/tcp open telnet

25/tcp open smtp

80/tcp closed http

110/tcp closed pop3

139/tcp open netbios-ssn

443/tcp closed https

445/tcp closed microsoft-ds

3389/tcp closed ms-term-serv

MAC Address: 00:60:B0:59:B6:14 (Hewlett-packard CO.)

Nmap done: 1 IP address (1 host up) scanned in 0.22 seconds

Performing a top port scan on the ten highest ranked ports

By default, Nmap will scan the 1000 most commonly used ports. The -F option (see

page 81) reduces that number to 100. Using the --top-ports option, you can specify

any number of top ranked ports to scan.

The example above demonstrates using the --top-ports option to scan the top 10

ports; however, any number can be used. For example: nmap --top-ports 500 would

scan the top 500 most commonly used ports and nmap --top-ports 5000 would scan

the top 5000 most commonly used ports.

Perform a Sequential Port Scan

The -r option performs a sequential port scan on the specified target.

Usage syntax: nmap -r [target]

$ nmap -r 10.10.1.48

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 13:02 CDT

Interesting ports on 10.10.1.48:

Not shown: 994 closed ports

PORT STATE SERVICE

21/tcp open ftp

22/tcp open ssh

25/tcp open smtp

80/tcp open http

111/tcp open rpcbind

2049/tcp open nfs

Nmap done: 1 IP address (1 host up) scanned in 0.49 seconds

Performing a sequentially ordered port scan

Nmap’s default scanning algorithm randomizes the port scan order. This is useful for

evading firewalls and intrusion prevention systems. The -r parameter overrides this

functionality and instructs Nmap to sequentially search for open ports in numerical

order.

Note

The results of the -r scan aren’t entirely evident because Nmap always

sorts the final output of each scan. Combining the -v option with -r will

display the sequential port discovery in real time.

Section 6:

Operating System and Service Detection

Version Detection Overview

One of Nmap’s most remarkable (and incredibly useful) features is its ability to

detect operating systems and services on remote systems. This feature analyzes

responses from scanned targets and attempts to identify the host’s operating

system and installed services.

The process of identifying a target’s operating system and software versions is

known as TCP/IP fingerprinting. Although it is not an exact science, Nmap

developers have taken great care in making TCP/IP fingerprinting an accurate and

reliable feature. And, like most of Nmap’s features, version detection can be

controlled using an array of arguments which are covered in this section.

Summary of features covered in this section:

Feature

Option

Operating System Detection

-O

Attempt to Guess an Unknown OS

--osscan-guess

Service Version Detection

-sV

Perform a RPC Scan

--version-trace

Troubleshooting Version Scans

-sR

Operating System Detection

The -O parameter enables Nmap’s operating system detection feature.

Usage syntax: nmap -O [target]

# nmap -O 10.10.1.48

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-11 13:09 Central

Daylight Time

...

MAC Address: 00:0C:29:D5:38:F4 (VMware)

Device type: general purpose

Running: Linux 2.6.X

OS details: Linux 2.6.9 - 2.6.28

Network Distance: 1 hop

...

Output of Nmap’s operating system detection feature

As demonstrated above, Nmap is (in most cases) able to identify the operating

system on a remote target. Operating system detection is performed by analyzing

responses from the target for a set of predictable characteristics which can be used

to identify the type of OS on the remote system.

In order for OS detection to work properly there must be at least one open and one

closed port on the target system. When scanning multiple targets, the --osscan-limit

option can be combined with -O to instruct Nmap not to OS scan hosts that do not

meet this criteria.

Tip

The -v option can be combined with -O to display additional information

Nmap discovers about the remote system.

Submitting TCP/IP Fingerprints

If Nmap is unable to determine the operating system on a target, it will provide a

fingerprint which can be submitted to Nmap’s OS database at

www.nmap.org/submit/. The example below demonstrates Nmap’s output in this

scenario.

# nmap -O 10.10.1.11

Starting Nmap 5.00 ( http://nmap.org ) at 2009-12-16 14:16 Central

Standard Time

...

No exact OS matches for host (If you know what OS is running on it,

see http://nmap.org/submit/ ).

TCP/IP fingerprint:

OS:SCAN(V=5.00%D=12/16%OT=3001%CT=1%CU=32781%PV=Y%DS=1%G=Y%M=00204A%TM=4B29

OS:4048%P=i686-pc-windows-windows)SEQ(CI=I%II=I%TS=U)OPS(O1=M400%O2=%O3=%O4

OS:=%O5=%O6=)OPS(O1=M400%O2=M400%O3=%O4=%O5=%O6=)OPS(O1=%O2=M400%O3=M400%O4

OS:=%O5=%O6=)OPS(O1=%O2=%O3=M400%O4=%O5=%O6=)OPS(O1=M400%O2=%O3=M400%O4=%O5

OS:=%O6=)WIN(W1=7FF%W2=0%W3=0%W4=0%W5=0%W6=0)WIN(W1=7FF%W2=7FF%W3=0%W4=0%W5

OS:=0%W6=0)WIN(W1=0%W2=7FF%W3=7FF%W4=0%W5=0%W6=0)WIN(W1=0%W2=0%W3=7FF%W4=0%

OS:W5=0%W6=0)WIN(W1=7FF%W2=0%W3=7FF%W4=0%W5=0%W6=0)ECN(R=Y%DF=Y%T=40%W=0%O=

OS:%CC=N%Q=)T1(R=Y%DF=Y%T=40%S=O%A=S+%F=AS%RD=0%Q=)T1(R=Y%DF=Y%T=40%S=O%A=O

OS:%F=AS%RD=0%Q=)T1(R=Y%DF=Y%T=40%S=Z%A=S+%F=AR%RD=0%Q=)T2(R=Y%DF=Y%T=40%W=

OS:0%S=Z%A=S+%F=AR%O=%RD=0%Q=)T3(R=Y%DF=Y%T=40%W=0%S=Z%A=S+%F=AR%O=%RD=0%Q=

OS:)T4(R=Y%DF=Y%T=40%W=0%S=A%A=Z%F=R%O=%RD=0%Q=)T5(R=Y%DF=Y%T=40%W=0%S=Z%A=

OS:S+%F=AR%O=%RD=0%Q=)T6(R=Y%DF=Y%T=40%W=0%S=A%A=Z%F=R%O=%RD=0%Q=)T7(R=Y%DF

OS:=Y%T=40%W=0%S=Z%A=S+%F=AR%O=%RD=0%Q=)U1(R=Y%DF=Y%T=40%IPL=38%UN=0%RIPL=G

OS:%RID=G%RIPCK=G%RUCK=G%RUD=G)IE(R=Y%DFI=S%T=40%CD=S)

...

TCP/IP fingerprint generated by Nmap

By submitting the fingerprint generated and correctly identifying the target system’s

operating system, you can help improve the accuracy of Nmap’s OS detection

feature in future releases.

Attempt to Guess an Unknown Operating System

If Nmap is unable to accurately identify the OS, you can force it to guess by using

the --osscan-guess option.

Usage syntax: nmap -O --osscan-guess [target]

# nmap -O --osscan-guess 10.10.1.11

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-17 13:25 CDT

Interesting ports on 10.10.1.11:

Not shown: 999 closed ports

PORT STATE SERVICE

3001/tcp open nessus

MAC Address: 00:20:4A:69:FD:94 (Pronet Gmbh)

Aggressive OS guesses: Enerdis Enerium 200 energy monitoring device or

Mitsubishi XD1000 projector (96%), Lantronix UDS200 external serial

device server (96%), Lantronix Xport-03 embedded serial device server

(firmware 6.1.0.3) (95%), Larus 54580 NTP server (95%), Lantronix

Evolution OS (93%), Lantronix UDS1100 external serial device server

(92%), Lantronix XPort embedded Ethernet device server (90%),

Stonewater Control Systems environmental monitoring appliance (88%),

FreeBSD 6.3-PRERELEASE (88%), Crestron MC2E, MP2E, PRO2, or QM-RMC

control and automation system (2-Series) (87%)

...

Nmap operating system guess output

The example above displays a list of possible matches for the target’s operating

system. Each guess is listed with a percentage of confidence Nmap has in the

supplied match.

Tip

The --fuzzy option is a synonym that can be used as an easy to remember

shortcut for the --osscan-guess feature.

Service Version Detection

The -sV parameter enables Nmap’s service version detection feature.

Usage syntax: nmap -sV [target]

# nmap -sV 10.10.1.48

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-11 12:49 Central

Daylight Time

Interesting ports on 10.10.1.48:

Not shown: 996 closed ports

PORT STATE SERVICE VERSION

21/tcp open ftp vsftpd 2.0.6

22/tcp open ssh OpenSSH 4.7p1 Debian 8ubuntu1.2 (protocol 2.0)

25/tcp open smtp Postfix smtpd

80/tcp open http Apache httpd 2.2.8 ((Ubuntu))

MAC Address: 00:0C:29:D5:38:F4 (VMware)

Service Info: Host: 10.10.1.48; OSs: Unix, Linux

Service detection performed. Please report any incorrect results at

http://nmap.org/submit/ .

Nmap done: 1 IP address (1 host up) scanned in 8.33 seconds

Output of Nmap’s service version detection feature

The -sV option will attempt to identify the vendor and software version for any

open ports it detects. The results of the above scan show the software vendor and

version number for services that Nmap was successfully able to identify.

Note

Nmap version detection purposely skips some problematic ports

(specifically 9100-9107). This can be overridden by combining the

--allports parameter with -sV which instructs Nmap not to exclude any

ports from version detection.

Troubleshooting Version Scans

The --version-trace option can be enabled to display verbose version scan activity.

Usage syntax: nmap -sV --version-trace [target]

$ nmap -sV --version-trace 10.10.1.48

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 13:16 CDT

PORTS: Using top 1000 ports found open (TCP:1000, UDP:0, SCTP:0)

--------------- Timing report ---------------

hostgroups: min 1, max 100000

rtt-timeouts: init 1000, min 100, max 10000

max-scan-delay: TCP 1000, UDP 1000, SCTP 1000

parallelism: min 0, max 0

max-retries: 10, host-timeout: 0

min-rate: 0, max-rate: 0

---------------------------------------------

NSE: Loaded 3 scripts for scanning.

Overall sending rates: 319.95 packets / s.

Increased max_successful_tryno for 10.10.1.48 to 1 (packet drop)

Overall sending rates: 756.69 packets / s.

NSOCK (1.6000s) TCP connection requested to 10.10.1.48:21 (IOD #1) EID 8

NSOCK (1.6000s) TCP connection requested to 10.10.1.48:22 (IOD #2) EID 16

NSOCK (1.6000s) TCP connection requested to 10.10.1.48:25 (IOD #3) EID 24

NSOCK (1.6000s) TCP connection requested to 10.10.1.48:80 (IOD #4) EID 32

NSOCK (1.6000s) TCP connection requested to 10.10.1.48:111 (IOD #5) EID 40

NSOCK (1.6000s) TCP connection requested to 10.10.1.48:2049 (IOD #6) EID 48

NSOCK (1.6000s) nsock_loop() started (no timeout). 6 events pending

NSOCK (1.6010s) Callback: CONNECT SUCCESS for EID 8 [10.10.1.48:21]

...

Version scan trace output

The --version-trace option can be helpful for debugging problems or to gain

additional information about the target system. For more information about

troubleshooting and debugging Nmap see Section 10.

Perform an RPC Scan

The -sR option performs a RPC (Remote Procedure Call) scan on the specified target.

Usage syntax: nmap -sR [target]

$ nmap -sR 10.10.1.176

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 14:22 Central

Daylight Time

Interesting ports on 10.10.1.176:

Not shown: 995 closed ports

PORT STATE SERVICE VERSION

22/tcp open ssh

111/tcp open rpcbind (rpcbind V2) 2 (rpc #100000)

139/tcp open netbios-ssn

445/tcp open microsoft-ds

2049/tcp open nfs (nfs V2-4) 2-4 (rpc #100003)

MAC Address: 00:16:EA:F0:92:50 (Intel)

Nmap done: 1 IP address (1 host up) scanned in 3.01 seconds

Output of a RPC scan

The output of the -sR scan above displays information about RPC services running

on the target system. RCP is most commonly associated with Unix and Linux systems

specifically for the NFS (Network File System) service. In this example, NFS version 2

RPC services are detected on ports 111 and 2049.

Section 7:

Timing Options

Timing Options Overview

Many Nmap features have configurable timing options. These timing options can be

used to speed up or slow down scanning operations depending on your needs.

When scanning a large number of hosts on a fast network you may want to increase

the number of parallel operations to get faster results. Alternatively, when scanning

slow networks (or across the internet) you may want to slow down a scan to get

more accurate results or to evade intrusion detection systems. This section

discusses the options available for these timing features.

Summary of features covered in this section:

Feature

Option

Timing Templates

-T[0-5]

Set the Packet TTL

--ttl

Minimum # of Parallel Operations

--min-parallelism

Maximum # of Parallel Operations

--max-parallelism

Minimum Host Group Size

--min-hostgroup

Maximum Host Group Size

--max-hostgroup

Maximum RTT Timeout

--max-rtt-timeout

Initial RTT Timeout

--initial-rtt-timeout

Maximum Retries

--max-retries

Host Timeout

--host-timeout

Minimum Scan Delay

--scan-delay

Maximum Scan Delay

--max-scan-delay

Minimum Packet Rate

--min-rate

Maximum Packet Rate

--max-rate

Defeat Reset Rate Limits

--defeat-rst-ratelimit

Timing Parameters

Nmap timing parameters are accepted as milliseconds by default. You can also

specify timing parameters in seconds, minutes, or hours by appending a qualifier to

the time argument. The table below provides examples of time parameter usage

syntax.

Parameter

Definition

Example

Meaning

(none)

Milliseconds (1/1000 of a second)

500

500 milliseconds

Seconds

300s

300 seconds

Minutes

5 minutes

Hours

1 hour

Nmap time specification parameters

Example: The --host-timeout option (see page 108) uses a timing parameter. To

specify a five minute timeout you can use any of the following forms of time

specification:

nmap --host-timeout 300000 10.10.5.11

nmap --host-timeout 300s 10.10.5.11

nmap --host-timeout 5m 10.10.5.11

Since 300000 = 300s = 5m any of the above commands will produce the same result.

100

Timing Templates

The -T parameter is used to specify a timing template for an Nmap scan.

Usage syntax: nmap -T[0-5] [target]

$ nmap -T4 10.10.1.1

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-12 16:59 CDT

Interesting ports on 10.10.1.1:

Not shown: 998 closed ports

PORT STATE SERVICE

80/tcp open http

443/tcp open https

Nmap done: 1 IP address (1 host up) scanned in 0.48 seconds

Using a timing template

Timing templates are handy shortcuts for various timing options (discussed later in

this section). There are six templates (numbered 0-5) that can be used to speed up

scanning (for faster results) or to slow down scanning (to evade firewalls). The table

below describes each timing template.

Template

Name

Notes

-T0

paranoid

Extremely slow

-T1

sneaky

Useful for avoiding intrusion detection systems

-T2

polite

Unlikely to interfere with the target system

-T3

normal

This is the default timing template

-T4

aggressive

Produces faster results on local networks

-T5

insane

Very fast and aggressive scan

Nmap timing templates

101

Minimum Number of Parallel Operations

The --min-parallelism option is used to specify the minimum number of parallel

port scan operations Nmap should perform at any given time.

Usage syntax: nmap --min-parallelism [number] [target]

# nmap --min-parallelism 100 10.10.1.70

Starting Nmap 5.00 ( http://nmap.org ) at 2009-12-17 09:02 CST

Interesting ports on 10.10.1.70:

Not shown: 994 filtered ports

PORT STATE SERVICE

139/tcp open netbios-ssn

445/tcp open microsoft-ds

2967/tcp closed symantec-av

5900/tcp open vnc

19283/tcp closed unknown

19315/tcp closed unknown

MAC Address: 00:0C:F1:A6:1F:16 (Intel)

Nmap done: 1 IP address (1 host up) scanned in 3.43 seconds

Specifying the minimum number of parallel operations

Nmap automatically adjusts parallel scanning options based on network conditions.

In some rare cases you may want to specify custom settings. The above example

instructs Nmap to always perform at least 100 parallel operations at any given time.

Note

While manually setting the --min-parallelism option may increase scan

performance, setting it too high may produce inaccurate results.

102

Maximum Number of Parallel Operations

The --max-parallelism option is used to control the maximum number of parallel

port scan operations Nmap will perform at any given time.

Usage syntax: nmap --max-parallelism [number] [target]

# nmap --max-parallelism 1 10.10.1.70

Starting Nmap 5.00 ( http://nmap.org ) at 2009-12-17 09:03 CST

Interesting ports on 10.10.1.70:

Not shown: 994 filtered ports

PORT STATE SERVICE

139/tcp open netbios-ssn

445/tcp open microsoft-ds

2967/tcp closed symantec-av

5900/tcp open vnc

19283/tcp closed unknown

19315/tcp closed unknown

MAC Address: 00:0C:F1:A6:1F:16 (Intel)

Nmap done: 1 IP address (1 host up) scanned in 213.76 seconds

Specifying the maximum number of parallel operations

In the above example --max-parallelism 1 is used to restrict Nmap so that only one

operation is performed at a time. This scan will be considerably slow, but will be less

likely to overwhelm the target system with a flood of packets.

103

Minimum Host Group Size

The --min-hostgroup option is used to specify the minimum number of targets

Nmap should scan in parallel.

Usage syntax: nmap --min-hostgroup [number] [targets]

# nmap --min-hostgroup 30 10.10.1.0/24

Starting Nmap 5.00 ( http://nmap.org ) at 2009-11-10 10:17 CST

Interesting ports on 10.10.1.1:

Not shown: 998 closed ports

PORT STATE SERVICE

80/tcp open http

443/tcp open https

MAC Address: 00:06:B1:12:0D:14 (Sonicwall)

Interesting ports on 10.10.1.2:

Not shown: 998 closed ports

PORT STATE SERVICE

23/tcp open telnet

80/tcp open http

MAC Address: 00:19:B9:A6:ED:D9 (Dell)

...

Specifying a minimum host group size

Nmap will perform scans in parallel to save time when scanning multiple targets

such as a range or entire subnet. By default, Nmap will automatically adjust the size

of the host groups based on the type of scan being performed and network

conditions. By specifying the --min-hostgroup option, Nmap will attempt to keep

the group sizes above the specified number.

104

Maximum Host Group Size

The --max-hostgroup option is used to specify the maximum number of targets

Nmap should scan in parallel.

Usage syntax: nmap --max-hostgroup [number] [targets]

# nmap --max-hostgroup 10 10.10.1.0/24

Starting Nmap 5.00 ( http://nmap.org ) at 2009-11-10 10:18 CST

Interesting ports on 10.10.1.1:

Not shown: 998 closed ports

PORT STATE SERVICE

80/tcp open http

443/tcp open https

MAC Address: 00:06:B1:12:0D:14 (Sonicwall)

Interesting ports on 10.10.1.2:

Not shown: 998 closed ports

PORT STATE SERVICE

23/tcp open telnet

80/tcp open http

MAC Address: 00:19:B9:A6:ED:D9 (Dell)

...

Specifying a maximum host group size

In contrast to the --min-hostgroup option, the --max-hostgroup option controls the

maximum number of hosts in a group. This option is helpful if you want to reduce

the load on a network or to avoid triggering any red flags with various network

security products.

105

Initial RTT Timeout

The --initial-rtt-timeout option controls the initial RTT (round-trip time) timeout

value used by Nmap.

Usage syntax: nmap --initial-rtt-timeout [time] [target]

# nmap --initial-rtt-timeout 5000 scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-12-16 16:23 CST

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 998 filtered ports

PORT STATE SERVICE

53/tcp open domain

80/tcp open http

Nmap done: 1 IP address (1 host up) scanned in 8.31 seconds

Specifying the initial RTT timeout value used by Nmap

The default timing template (-T3; see page 100) has an --initial-rtt-timeout value of

1000 milliseconds. Increasing the value will reduce the number of packet

retransmissions due to timeouts. By decreasing the value you can speed up scans;

but do so with caution. Setting the RTT timeout value too low can negate any

potential performance gains and lead to inaccurate results.

106

Maximum RTT Timeout

The --max-rtt-timeout option is used to specify the maximum RTT (Round-Trip

Time) timeout for a packet response.

Usage syntax: nmap --max-rtt-timeout [time] [target]

# nmap --max-rtt-timeout 400 scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-11-14 12:57 CST

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 993 filtered ports

PORT STATE SERVICE

25/tcp closed smtp

53/tcp open domain

70/tcp closed gopher

80/tcp open http

110/tcp closed pop3

113/tcp closed auth

31337/tcp closed Elite

Nmap done: 1 IP address (1 host up) scanned in 8.11 seconds

Specifying a 400 millisecond maximum RTT timeout

Nmap dynamically adjusts RTT timeout options for best results by default. The

default maximum RTT timeout is 10 seconds. Manually adjusting the maximum RTT

timeout lower will allow for faster scan times (especially when scanning large blocks

of addresses). Specifying a high maximum RTT timeout will prevent Nmap from

giving up too soon when scanning over slow/unreliable connections. Typical values

are between 100 milliseconds for fast/reliable networks and 10000 milliseconds for

slow/unreliable connections.

107

Maximum Retries

The --max-retries option is used to control the maximum number of probe

retransmissions Nmap will attempt to perform.

Usage syntax: nmap --max-retries [number] [target]

# nmap --max-retries 1 scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-11-10 09:59 CST

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 993 filtered ports

PORT STATE SERVICE

25/tcp closed smtp

53/tcp open domain

70/tcp closed gopher

80/tcp open http

110/tcp closed pop3

113/tcp closed auth

31337/tcp closed Elite

Nmap done: 1 IP address (1 host up) scanned in 7.55 seconds

Specifying the maximum number of retries

By default, Nmap will automatically adjust the number of probe retransmissions

based on network conditions. The --max-retries option can be used if you want to

override the default settings or troubleshoot a connectivity problem. Specifying a

high number can increase the time it takes for a scan to complete, but will produce

more accurate results. By lowering the --max-retries you can speed up a scan –

although you may not get accurate results if Nmap gives up too quickly.

108

Set the Packet TTL

The --ttl option is used to specify the TTL (time-to-live) for the specified scan (in

milliseconds).

Usage syntax: nmap --ttl [time] [target]

# nmap --ttl 500 scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-24 13:19 CDT

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 993 filtered ports

PORT STATE SERVICE

25/tcp closed smtp

53/tcp open domain

70/tcp closed gopher

80/tcp open http

110/tcp closed pop3

113/tcp closed auth

31337/tcp closed Elite

Nmap done: 1 IP address (1 host up) scanned in 7.04 seconds

Specifying a TTL parameter of 500 milliseconds

Packets sent using this option will have the specified TTL value. This option is useful

when scanning targets on slow connections where normal packets may time out

before receiving a response.

109

Host Timeout

The --host-timeout option causes Nmap to give up on slow hosts after the specified

time.

Usage syntax: nmap --host-timeout [time] [target]

# nmap --host-timeout 1m 10.10.5.11

Starting Nmap 5.00 ( http://nmap.org ) at 2009-10-09 13:29 CDT

Skipping host 10.10.5.11 due to host timeout

Nmap done: 1 IP address (1 host up) scanned in 60.19 seconds

Output of a Nmap scan when specifying a 1 minute timeout

A host may take a long time to scan if it is located on a slow or unreliable network.

Systems that are protected by rate limiting firewalls may also take a considerable

amount of time to scan. The --host-timeout option instructs Nmap to give up on the

target system if it fails to complete after the specified time interval. In the above

example, the scan takes longer than one minute to complete (as specified by the 1m

parameter) which causes Nmap to terminate the scan. This option is particularly

useful when scanning multiple systems across a WAN or internet connection.

Note

Nmap performs parallel operations when scanning multiple targets. In the

event that one host is taking a long time to respond, Nmap is likely

scanning other hosts during that time. This reduces potential bottlenecks

that slow hosts can create.

Warning

When the --host-timeout option is specified, Nmap will not display any

results if a host exceeds the timeout (even if it discovered open ports).

110

Minimum Scan Delay

The --scan-delay option instructs Nmap to pause for the specified time interval

between probes.

Usage syntax: nmap --scan-delay [time] [target]

# nmap --scan-delay 5s scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-11-04 13:29 CST

Interesting ports on 64.13.134.52:

Not shown: 993 filtered ports

PORT STATE SERVICE

25/tcp closed smtp

53/tcp open domain

70/tcp closed gopher

80/tcp open http

110/tcp closed pop3

113/tcp closed auth

31337/tcp closed Elite

Nmap done: 1 IP address (1 host up) scanned in 229.28 seconds

Specifying a 5 second minimum scan delay

Some systems employ rate limiting which can hamper Nmap scanning attempts.

Nmap will automatically adjust the scan delay by default on systems where rate

limiting is detected. In some cases it may be useful to specify your own scan delay if

you know that rate limiting or IDS (Intrusion Detection Systems) are in use. In the

example above the scan delay of 5s instructs Nmap to wait five seconds between

probes.

111

Maximum Scan Delay

The --max-scan-delay is used to specify the maximum amount of time Nmap should

wait between probes.

Usage syntax: nmap --max-scan-delay [time] [target]

# nmap --max-scan-delay 300 scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-11-09 15:35 CST

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 993 filtered ports

PORT STATE SERVICE

25/tcp closed smtp

53/tcp open domain

70/tcp closed gopher

80/tcp open http

110/tcp closed pop3

113/tcp closed auth

31337/tcp closed Elite

Nmap done: 1 IP address (1 host up) scanned in 8.14 seconds

Specifying a 30 millisecond maximum scan delay

Nmap automatically adjusts the scan delay to adjust for network conditions and/or

rate limiting hosts. The --max-scan-delay option can be used to provide an upper

limit to the amount of time between probes. This can speed up a scan, but comes at

the expense of accurate results and added network stress.

112

Minimum Packet Rate

The --min-rate option is used to specify the minimum number of packets Nmap

should send per second.

Usage syntax: nmap --min-rate [number] [target]

# nmap --min-rate 30 scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-11-10 14:13 CST

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 993 filtered ports

PORT STATE SERVICE

25/tcp closed smtp

53/tcp open domain

70/tcp closed gopher

80/tcp open http

110/tcp closed pop3

113/tcp closed auth

31337/tcp closed Elite

Nmap done: 1 IP address (1 host up) scanned in 6.99 seconds

Specifying a minimum packet transmission rate of 30

Nmap, by default, will automatically adjust the packet rate for a scan based on

network conditions. In some cases you may want to specify your own minimum

rate - although this is generally not recommended. In the above example

--min-rate 30 instructs Nmap to send at least 30 packets per a second. Nmap will

use the number as a low threshold but may scan faster than this if network

conditions allow.

Warning

Setting the --min-rate too high may reduce the accuracy of a scan.

113

Maximum Packet Rate

The --max-rate option is used to specify the maximum number of packets Nmap

should send per second.

Usage syntax: nmap --max-rate [number] [target]

# nmap --max-rate 30 scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-11-10 14:14 CST

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 993 filtered ports

PORT STATE SERVICE

25/tcp closed smtp

53/tcp open domain

70/tcp closed gopher

80/tcp open http

110/tcp closed pop3

113/tcp closed auth

31337/tcp closed Elite

Nmap done: 1 IP address (1 host up) scanned in 68.51 seconds

Specifying a maximum packet transmission rate of 30

In the example above, specifying --max-rate 30 instructs Nmap to send no more

that 30 packets per second. This can dramatically slow down a scan but can be

helpful when attempting to avoid intrusion detection systems or a target that uses

rate limiting.

Tip

To perform a very sneaky scan use --max-rate 0.1 which instructs Nmap to

send one packet every ten seconds.

114

Defeat Reset Rate Limits

The --defeat-rst-ratelimit is used to defeat targets that apply rate limiting to RST

(reset) packets.

Usage syntax: nmap --defeat-rst-ratelimit [target]

# nmap --defeat-rst-ratelimit scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-11-10 15:14 CST

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 993 filtered ports

PORT STATE SERVICE

25/tcp closed smtp

53/tcp open domain

70/tcp closed gopher

80/tcp open http

110/tcp closed pop3

113/tcp closed auth

31337/tcp closed Elite

Nmap done: 1 IP address (1 host up) scanned in 7.71 seconds

Defeating RST rate limits

The --defeat-rst-ratelimit option can be useful if you want to speed up scans on

targets that implement RST packet rate limits. It can, however, lead to inaccurate

results and as such it is rarely used.

Note

The --defeat-rst-ratelimit option is rarely used because, in most cases,

Nmap will automatically detect rate limiting hosts and adjust itself

accordingly.

115

Section 8:

Evading Firewalls

116

Firewall Evasion Techniques Overview

Firewalls and intrusion prevention systems are designed to prevent tools like Nmap

from getting an accurate picture of the systems they are protecting. Nmap includes

a number of features designed to circumvent these defenses. This section discusses

the various evasion techniques built into Nmap.

Summary of features covered in this section:

Feature

Option

Fragment Packets

-f

Specify a Specific MTU

--mtu

Use a Decoy

-D

Idle Zombie Scan

-sI

Manually Specify a Source Port

--source-port

Append Random Data

--data-length

Randomize Target Scan Order

--randomize-hosts

Spoof MAC Address

--spoof-mac

Send Bad Checksums

--badsum

117

Fragment Packets

The -f option is used to fragment probes into 8-byte packets.

Usage syntax: nmap -f [target]

# nmap -f 10.10.1.48

Starting Nmap 5.00 ( http://nmap.org ) at 2009-11-11 10:10 CST

Interesting ports on 10.10.1.48:

Not shown: 994 closed ports

PORT STATE SERVICE

21/tcp open ftp

22/tcp open ssh

25/tcp open smtp

80/tcp open http

111/tcp open rpcbind

2049/tcp open nfs

MAC Address: 00:0C:29:D5:38:F4 (VMware)

Nmap done: 1 IP address (1 host up) scanned in 1.52 seconds

Scanning a target using fragmented packets

The -f option instructs Nmap to send small 8-byte packets thus fragmenting the

probe into many very small packets. This option isn’t particularly useful in everyday

situations; however, it may be helpful when attempting to evade some older or

improperly configured firewalls.

Tip

Some host operating systems may require the use of --send-eth combined

with -f for fragmented packets to be properly transmitted.

118

Specify a Specific MTU

The --mtu option is used to specify a custom MTU (Maximum Transmission Unit).

Usage syntax: nmap --mtu [number] [target]

# nmap --mtu 16 10.10.1.48

Starting Nmap 5.00 ( http://nmap.org ) at 2009-11-11 10:11 CST

Interesting ports on 10.10.1.48:

Not shown: 994 closed ports

PORT STATE SERVICE

21/tcp open ftp

22/tcp open ssh

25/tcp open smtp

80/tcp open http

111/tcp open rpcbind

2049/tcp open nfs

MAC Address: 00:0C:29:D5:38:F4 (VMware)

Nmap done: 1 IP address (1 host up) scanned in 0.34 seconds

Specifying a specific MTU

The --mtu option is similar to the -f option (discussed on page 117) except it allows

you to specify your own MTU to be used during scanning. This creates fragmented

packets that can potentially confuse some firewalls. In the above example, the

--mtu 16 argument instructs Nmap to use tiny 16-byte packets for the scan.

Note

The MTU must be a multiple of 8 (example 8, 16, 24, 32, etc).

Tip

Some host operating systems may require the use of --send-eth combined

with --mtu for fragmented packets to be properly transmitted.

119

Use a Decoy

The -D option is used to mask an Nmap scan by using one or more decoys.

Usage syntax: nmap -D [decoy1,decoy2,etc|RND:number] [target]

# nmap -D RND:10 10.10.1.48

Starting Nmap 5.00 ( http://nmap.org ) at 2009-11-02 16:41 CST

...

Masking a scan using 10 randomly generated decoy IP addresses

When performing a decoy scan Nmap will spoof additional packets from the

specified number of decoy addresses. This effectively makes it appear that the

target is being scanned by multiple systems simultaneously. Using decoys allows the

actual source of the scan to “blend into the crowd” which makes it harder to trace

where the scan is coming from.

In the above example nmap -D RND:10 instructs Nmap to generate 10 random

decoys. You can also specify decoy addresses manually using the following syntax:

nmap -D decoy1,decoy2,decoy3,etc.

Warning

Using too many decoys can cause network congestion and reduce the

effectiveness of a scan. Additionally, some internet service providers

may filter spoofed traffic which will reduce the effectiveness of using

decoys to cloak your scanning activity.

120

Idle Zombie Scan

The -sI option is used to perform an idle zombie scan.

Usage syntax: nmap -sI [zombie host] [target]

# nmap -sI 10.10.1.41 10.10.1.252

Starting Nmap 5.00 ( http://nmap.org ) at 2009-11-14 18:35 CST

Idle scan using zombie 10.10.1.41 (10.10.1.41:443); Class: Incremental

Interesting ports on 10.10.1.252:

Not shown: 997 closed|filtered ports

PORT STATE SERVICE

135/tcp open msrpc

139/tcp open netbios-ssn

445/tcp open microsoft-ds

MAC Address: 00:25:64:D7:FF:59 (Dell)

Nmap done: 1 IP address (1 host up) scanned in 8.29 seconds

Using an idle “zombie” to scan a target

The idle zombie scan is a unique scanning technique that allows you to exploit an

idle system and use it to scan a target system for you. In this example 10.10.1.41 is

the zombie and 10.10.1.252 is the target system. The scan works by exploiting the

predictable IP sequence ID generation employed by some systems. In order for an

idle scan to be successful, the zombie system must truly be idle at the time of

scanning.

Note

With this scan no probe packets are sent from your system to the target;

although an initial ping packet will be sent to the target unless you

combine -PN with -sI.

More information about the idle zombie scan can be found on the Nmap website at

www.nmap.org/book/idlescan.html.

121

Manually Specify a Source Port Number

The --source-port option is used to manually specify the source port number of a

probe.

Usage syntax: nmap --source-port [port] [target]

# nmap --source-port 53 scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-12-16 16:41 CST

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 993 filtered ports

PORT STATE SERVICE

25/tcp closed smtp

53/tcp open domain

70/tcp closed gopher

80/tcp open http

110/tcp closed pop3

113/tcp closed auth

31337/tcp closed Elite

Nmap done: 1 IP address (1 host up) scanned in 7.59 seconds

Manually specifying the packet source port number

Every TCP segment contains a source port number in addition to a destination. By

default, Nmap will randomly pick an available outgoing source port to probe a

target. The --source-port option will force Nmap to use the specified port as the

source for all packets. This technique can be used to exploit weaknesses in firewalls

that are improperly configured to blindly accept incoming traffic based on a specific

port number. Port 20 (FTP), port 53 (DNS), and 67 (DHCP) are common ports

susceptible to this type of scan.

Tip

The -g option is a shortcut that is synonymous with --source-port.

122

Append Random Data

The --data-length option can be used to append random data to probe packets.

Usage syntax: nmap --data-length [number] [target]

# nmap --data-length 25 10.10.1.252

Starting Nmap 5.00 ( http://nmap.org ) at 2009-11-14 18:41 CST

Interesting ports on 10.10.1.252:

Not shown: 995 filtered ports

PORT STATE SERVICE

135/tcp open msrpc

139/tcp open netbios-ssn

445/tcp open microsoft-ds

5800/tcp open vnc-http

5900/tcp open vnc

MAC Address: 00:25:64:D7:FF:59 (Dell)

Nmap done: 1 IP address (1 host up) scanned in 5.17 seconds

Padding a scan with random data to avoid detection

Nmap transmits packets which are generally a specific size. Some firewall vendors

know to look for this type of predictable packet size. The --data-length option adds

the specified amount of additional data to probes in an effort to circumvent these

types of checks. In the above example 25 additional bytes are added to all packets

sent to the target.

123

Randomize Target Scan Order

The --randomize-hosts option is used to randomize the scanning order of the

specified targets.

Usage syntax: nmap --randomize-hosts [targets]

$ nmap --randomize-hosts 10.10.1.100-254

Interesting ports on 10.10.1.109:

Not shown: 996 filtered ports

PORT STATE SERVICE

139/tcp open netbios-ssn

445/tcp open microsoft-ds

5800/tcp open vnc-http

5900/tcp open vnc

MAC Address: 00:1C:23:49:75:0C (Dell)

Interesting ports on 10.10.1.100:

Not shown: 996 filtered ports

PORT STATE SERVICE

139/tcp open netbios-ssn

445/tcp open microsoft-ds

5800/tcp open vnc-http

5900/tcp open vnc

MAC Address: 00:21:9B:3F:AC:EC (Dell)

Interesting ports on 10.10.1.107:

Not shown: 997 closed ports

PORT STATE SERVICE

22/tcp open ssh

139/tcp open netbios-ssn

...

Scanning systems in a random order

The --randomize-hosts option helps prevent scans of multiple targets from being

detected by firewalls and intrusion detection systems. This is done by scanning them

in a random order instead of sequential.

124

Spoof MAC Address

The --spoof-mac is used to spoof the MAC (Media Access Control) address of an

ethernet device.

Usage syntax: nmap --spoof-mac [vendor|MAC|0] [target]

# nmap -sT -PN --spoof-mac 0 192.168.1.1

Starting Nmap 5.00 ( http://nmap.org ) at 2010-01-15 19:48 CST

Spoofing MAC address 00:01:02:25:56:AE (3com)

Interesting ports on 192.168.1.1:

Not shown: 995 filtered ports

PORT STATE SERVICE

20/tcp closed ftp-data

21/tcp closed ftp

23/tcp closed telnet

80/tcp open http

2869/tcp open unknown

Nmap done: 1 IP address (1 host up) scanned in 4.78 seconds

Using a spoofed MAC address

In this example, Nmap is instructed to forge a randomly generated 3com MAC

address. This makes your scanning activity harder to trace by preventing your MAC

address from being logged on the target system.

The --spoof-mac option can be controlled by the following parameters:

Argument

Function

0 (zero)

Generates a random MAC address

Specific MAC Address

Uses the specified MAC address

Vendor Name

Generates a MAC address from the specified vendor

(such as Apple, Dell, 3Com, etc)

MAC address spoofing options

125

Send Bad Checksums

The --badsum option is used to send packets with incorrect checksums to the

specified host.

Usage syntax: nmap --badsum [target]

# nmap --badsum 10.10.1.41

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-24 16:19 CDT

All 1000 scanned ports on 10.10.1.41 are filtered

MAC Address: 00:60:B0:59:B6:14 (Hewlett-packard CO.)

Nmap done: 1 IP address (1 host up) scanned in 21.40 seconds

Scanning a target using bad checksums

The TCP/IP protocol uses checksums to ensure data integrity. Crafting packets with

bad checksums can, in some rare occasions, produce a response from a poorly

configured system. In the above example we did not receive any results, meaning

the target system is configured correctly. This is a typical result when using the

--badsum option.

Note

Only a poorly configured system would respond to a packet with a bad

checksum. Nevertheless, it is a good tool to use when auditing network

security or attempting to evade firewalls.

126

127

Section 9:

Output Options

128

Output Options Overview

Nmap offers several options for creating formatted output. In addition to displaying

the standard output on a screen, you can also save scan results in a text file, XML

file, or a single line grepable file. This feature can be helpful when scanning a large

number of systems or for comparing the results of two scans using the ndiff utility

(discussed in Section 13).

Note

The grep pattern matching utility is only available on Unix, Linux, and

Mac OS X systems by default. Windows users can download a Win32 port

of the GNU grep program at http://gnuwin32.sourceforge.net to use with

the examples discussed in this section.

Summary of features covered in this section:

Feature

Option

Save Output to a Text File

-oN

Save Output to a XML File

-oX

Grepable Output

-oG

Output All Supported File Types

-oA

Periodically Display Statistics

--stats-every

133t Output

-oS

129

Save Output to a Text File

The -oN parameter saves the results of a scan in a plain text file.

Usage syntax: nmap -oN [scan.txt] [target]

$ nmap -oN scan.txt 10.10.1.1

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 15:17 CDT

Interesting ports on 10.10.1.1:

Not shown: 998 closed ports

PORT STATE SERVICE

80/tcp open http

443/tcp open https

Nmap done: 1 IP address (1 host up) scanned in 0.47 seconds

Saving Nmap output in a text file

The results of the above scan are saved to the scan.txt file shown below.

$ cat scan.txt

# Nmap 5.00 scan initiated Thu Aug 13 15:17:16 2009 as: nmap -oN

scan.txt 10.10.1.1

Interesting ports on 10.10.1.1:

Not shown: 998 closed ports

PORT STATE SERVICE

80/tcp open http

443/tcp open https

# Nmap done at Thu Aug 13 15:17:17 2009 -- 1 IP address (1 host up)

scanned in 0.47 seconds

Reviewing the contents of the scan.txt file

Note

Nmap will overwrite an existing output file unless the --append-output

option is combined with -oN.

130

Save Output to a XML File

The -oX parameter saves the results of a scan in a XML file.

Usage syntax: nmap -oX [scan.xml] [target]

$ nmap -oX scan.xml 10.10.1.1

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 15:19 CDT

Interesting ports on 10.10.1.1:

Not shown: 998 closed ports

PORT STATE SERVICE

80/tcp open http

443/tcp open https

...

Creating a XML output file

The results of the above scan are saved to the scan.xml file shown below.

$ cat scan.xml

<?xml version="1.0" ?>

<?xml-stylesheet href="file:///usr/local/share/nmap/nmap.xsl"

type="text/xsl"?>

<!-- Nmap 5.00 scan initiated Thu Aug 13 15:19:44 2009 as: nmap -oX

scan.xml 10.10.1.1 -->

<nmaprun scanner="nmap" args="nmap -oX scan.xml 10.10.1.1"

start="1250194784" startstr="Thu Aug 13 15:19:44 2009" version="5.00"

...

Viewing the contents of the XML output file

The resulting XML file has hardcoded file paths which may only work the system

where the file was created. The --webxml parameter can be combined with -oX to

create a portable file for any system (with internet access). You can also specify an

alternative style sheet using the --stylesheet parameter. To avoid referencing a style

sheet at all, use the --no-stylesheet parameter.

131

Grepable Output

The -oG option enables grepable output.

Usage syntax: nmap -oG [scan.txt] [target]

$ nmap -oG scan.txt -F -O 10.10.1.1/24

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 15:50 CDT

Interesting ports on 10.10.1.1:

Not shown: 998 closed ports

PORT STATE SERVICE

80/tcp open http

443/tcp open https

...

Creating a grepable output file

The resulting scan is saved to the specified text file, which can be useful when

combined with text parsing tools like Perl or grep (as displayed below).

$ grep "Windows 98" scan.txt

Host: 10.10.1.217 Ports: 139/open/tcp//netbios-ssn///,

5800/open/tcp//vnc-http///, 5900/open/tcp//vnc/// Ignored State:

closed (97) OS: Microsoft Windows 98 SE Seq Index: 18 IP ID

Seq: Broken little-endian incremental

...

Using the grep utility to review a Nmap output file

In the above example, the grep utility will display all instances of the specified text

found in the scan.txt file. This makes it simple to quickly search for specific

information when analyzing results from a large scan.

132

Output All Supported File Types

The -oA parameter saves the output of a scan in text, grepable, and XML formats.

Usage syntax: nmap -oA [filename] [target]

$ nmap -oA scans 10.10.1.1

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 16:10 CDT

Interesting ports on 10.10.1.1:

Not shown: 998 closed ports

PORT STATE SERVICE

80/tcp open http

443/tcp open https

Nmap done: 1 IP address (1 host up) scanned in 0.66 seconds

Creating output files for all available formats

The resulting scan’s output files are created with their respective extensions as

displayed below.

$ ls -l scans.*

-rw-r--r-- 1 nick nick 284 2009-08-13 16:22 scans.gnmap

-rw-r--r-- 1 nick nick 307 2009-08-13 16:22 scans.nmap

-rw-r--r-- 1 nick nick 5150 2009-08-13 16:22 scans.xml

Directory listing of the resulting output files

File

Contents

scans.gnmap

Grepable output

scans.nmap

Plain text output

scans.xml

XML output

Nmap output files

133

Display Scan Statistics

The --stats-every option can be used to periodically display the status of the current

scan.

Usage syntax: nmap --stats-every [time] [target]

$ nmap --stats-every 5s 10.10.1.41

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 16:30 CDT

Stats: 0:00:07 elapsed; 0 hosts completed (1 up), 1 undergoing Service Scan

Service scan Timing: About 55.00% done; ETC: 16:30 (0:00:05 remaining)

Stats: 0:00:12 elapsed; 0 hosts completed (1 up), 1 undergoing Service Scan

Service scan Timing: About 85.00% done; ETC: 16:30 (0:00:02 remaining)

Stats: 0:00:17 elapsed; 0 hosts completed (1 up), 1 undergoing Service Scan

Service scan Timing: About 90.00% done; ETC: 16:30 (0:00:02 remaining)

Stats: 0:00:22 elapsed; 0 hosts completed (1 up), 1 undergoing Service Scan

Service scan Timing: About 90.00% done; ETC: 16:30 (0:00:02 remaining)

Stats: 0:00:27 elapsed; 0 hosts completed (1 up), 1 undergoing Service Scan

Service scan Timing: About 90.00% done; ETC: 16:30 (0:00:03 remaining)

Stats: 0:00:32 elapsed; 0 hosts completed (1 up), 1 undergoing Service Scan

...

Nmap scan status output

On slow scans you may get bored looking at your screen doing nothing for long

periods of time. The --stats-every option can alleviate this problem. In the above

example, --stats-every 5s instructs Nmap to display the status of the current scan

every five seconds. Timing parameters can be specified in seconds (s), minutes (m),

or hours (h) by appending an s, m, or h to the interval number as described on

page 99.

134

133t Output

The -oS option enables “script kiddie” output.

Usage syntax: nmap -oS [scan.txt] [target]

$ nmap -oS scan.txt 10.10.1.1

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 15:45 CDT

Interesting ports on 10.10.1.1:

Not shown: 998 closed ports

PORT STATE SERVICE

80/tcp open http

443/tcp open https

Nmap done: 1 IP address (1 host up) scanned in 0.48 seconds

Creating a “133t” output file

Script kiddie or “leet” speak is output is a cryptic form of typing used mostly by

immature teenagers on message boards and chat sites. This option is included as a

joke and isn’t really useful for anything other than a good laugh. The results of the

-oS option are saved in scan.txt file displayed below.

$ cat scan.txt

StaRtING NMap 5.00 ( htTp://nmap.oRg ) aT 2009-08-13 15:45 CDT

!nt3r3St|ng pOrts 0n 10.10.1.1:

n0t $h0wn: 998 cl0$3d p0rt$

P0RT $TATE seRV!CE

80/tcp Open hTtp

443/tcp 0pen httpS

Nmap DOnE: 1 Ip addresz (1 host up) $canned iN 0.48 $3c0nds

Nmap script kiddie output

135

Section 10:

Troubleshooting and Debugging

136

Troubleshooting and Debugging Overview

Technical problems are an inherent part of using computers. Nmap is no exception.

Occasionally a scan may not produce the output you expected; you may receive an

error – or you may not receive any output at all. Nmap offers several options for

tracing and debugging a scan which can help identify why this happens. The

following section describes these troubleshooting and debugging features in detail.

Summary of features covered in this section:

Feature

Option

Getting Help

-h

Display Nmap Version

-V

Verbose Output

-v

Debugging

-d

Display Port State Reason

--reason

Only Display Open Ports

--open

Trace Packets

--packet-trace

Display Host Networking

--iflist

Specify a Network Interface

-e

137

Getting Help

Executing nmap -h will display a summary of available options.

Usage syntax: nmap -h

$ nmap -h

Nmap 5.00 ( http://nmap.org )

Usage: nmap [Scan Type(s)] {target specification}

TARGET SPECIFICATION:

Can pass hostnames, IP addresses, networks, etc.

Ex: scanme.nmap.org, microsoft.com/24, 192.168.0.1; 10.0.0-255.1-254

-iL <inputfilename>: Input from list of hosts/networks

-iR <num hosts>: Choose random targets

--exclude <host1[,host2][,host3],...>: Exclude hosts/networks

--excludefile <exclude_file>: Exclude list from file

...

Displaying Nmap help information

For more detailed information you can read the Nmap manual page by typing

man nmap on the command line.

$ man nmap

Accessing the Nmap man page on Unix and Linux systems

Note

The man command is only available on Unix, Linux, and Mac OS X based

systems. Windows users can read the Nmap manual online at

www.nmap.org/book/man.html.

Tip

You can also find help online by subscribing to the Nmap mailing list at

www.seclists.org.

138

Display Nmap Version

The -V option is used to display the installed version of Nmap.

Usage syntax: nmap -V

$ nmap -V

Nmap version 5.00 ( http://nmap.org )

Displaying the installed version of Nmap

When troubleshooting Nmap problems you should always make sure you have the

most up-to-date version installed. Open source programs like Nmap are developed

at a rapid pace and bugs are typically fixed as soon as they are discovered. Compare

your installed version to the latest version available on the Nmap website at

www.nmap.org to make sure you are running the most up-to-date version available.

This will ensure that you have access to the latest features as well as the most bug-

free version available.

139

Verbose Output

The -v option is used to enable verbose output.

Usage syntax: nmap -v [target]

$ nmap -v scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-12 15:06 CDT

NSE: Loaded 0 scripts for scanning.

Initiating Ping Scan at 15:06

Scanning 64.13.134.52 [2 ports]

Completed Ping Scan at 15:06, 1.87s elapsed (1 total hosts)

Initiating Parallel DNS resolution of 1 host. at 15:06

Completed Parallel DNS resolution of 1 host. at 15:06, 0.16s elapsed

Initiating Connect Scan at 15:06

Scanning scanme.nmap.org (64.13.134.52) [1000 ports]

Discovered open port 53/tcp on 64.13.134.52

Discovered open port 80/tcp on 64.13.134.52

Completed Connect Scan at 15:06, 7.00s elapsed (1000 total ports)

Host scanme.nmap.org (64.13.134.52) is up (0.087s latency).

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 998 filtered ports

PORT STATE SERVICE

53/tcp open domain

80/tcp open http

Read data files from: /usr/local/share/nmap

Nmap done: 1 IP address (1 host up) scanned in 9.41 seconds

Nmap scan with verbose output enabled

Verbose output can be useful when troubleshooting connectivity problems, or if you

are simply interested in what’s going on behind the scenes of your scan.

Tip

You can use the -v option twice (-v -v or -vv) to enable additional verbose

output.

140

Debugging

The -d option enables debugging output.

Usage syntax: nmap -d[1-9] [target]

$ nmap -d scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-12 15:26 CDT

PORTS: Using top 1000 ports found open (TCP:1000, UDP:0, SCTP:0)

--------------- Timing report ---------------

hostgroups: min 1, max 100000

rtt-timeouts: init 1000, min 100, max 10000

max-scan-delay: TCP 1000, UDP 1000, SCTP 1000

parallelism: min 0, max 0

max-retries: 10, host-timeout: 0

min-rate: 0, max-rate: 0

---------------------------------------------

NSE: Loaded 0 scripts for scanning.

Initiating Ping Scan at 15:26

Scanning 64.13.134.52 [2 ports]

Completed Ping Scan at 15:26, 2.83s elapsed (1 total hosts)

Overall sending rates: 1.06 packets / s.

mass_rdns: Using DNS server 10.10.1.44

mass_rdns: Using DNS server 10.10.1.45

Initiating Parallel DNS resolution of 1 host. at 15:26

mass_rdns: 0.00s 0/1 [#: 2, OK: 0, NX: 0, DR: 0, SF: 0, TR: 1]

Completed Parallel DNS resolution of 1 host. at 15:26, 0.00s elapsed

...

Nmap debugging output

Debugging output provides additional information that can be use to trace bugs or

troubleshoot problems. The default -d output provides a fair amount of debugging

information. You can also specify a debugging level of 1-9 to be used with the -d

parameter to increase or decrease the amount of output. For example: -d1 provides

the lowest amount of debugging output and -d9 is the highest.

141

Display Port State Reason Codes

The --reason parameter displays the reason why a port is considered to be in the

given state.

Usage syntax: nmap --reason [target]

$ nmap --reason scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-12 15:43 CDT

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 993 filtered ports

Reason: 993 no-responses

PORT STATE SERVICE REASON

25/tcp closed smtp conn-refused

53/tcp open domain syn-ack

70/tcp closed gopher conn-refused

80/tcp open http syn-ack

110/tcp closed pop3 conn-refused

113/tcp closed auth conn-refused

31337/tcp closed Elite conn-refused

Nmap done: 1 IP address (1 host up) scanned in 8.83 seconds

Nmap scan with port state reason codes enabled

Notice the addition of the reason field in the above scan. Information in this field

can be useful when trying to determine why a target’s ports are in a particular state.

Ports that respond with syn-ack are considered to be open. Ports that respond with

conn-refused or reset are typically closed. Ports that do not respond at all are

generally filtered (by a firewall).

142

Only Display Open Ports

The --open parameter instructs Nmap to only display open ports.

Usage syntax: nmap --open [target]

$ nmap --open scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-12-18 12:47 CST

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 993 filtered ports, 5 closed ports

PORT STATE SERVICE

53/tcp open domain

80/tcp open http

Nmap done: 1 IP address (1 host up) scanned in 8.26 second

Limiting Nmap output to display open ports only

The --open parameter removes closed and filtered ports from the scan results. This

option is useful when you want to unclutter the results of your scan so that only

open ports are displayed. The same scan without the --open option is displayed

below for comparison.

$ nmap scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-12-18 12:49 CST

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 993 filtered ports

PORT STATE SERVICE

25/tcp closed smtp

53/tcp open domain

70/tcp closed gopher

80/tcp open http

110/tcp closed pop3

113/tcp closed auth

...

Nmap scan displaying open and closed ports

143

Trace Packets

The --packet-trace parameter instructs Nmap to display a summary of all packets

sent and received.

Usage syntax: nmap --packet-trace [target]

$ nmap --packet-trace 10.10.1.1

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 17:14 CDT

CONN (0.1600s) TCP localhost > 10.10.1.1:80 => Operation now in progress

CONN (0.1600s) TCP localhost > 10.10.1.1:443 => Operation now in progress

NSOCK (0.1610s) UDP connection requested to 10.10.1.45:53 (IOD #1) EID 8

NSOCK (0.1610s) Read request from IOD #1 [10.10.1.45:53] (timeout: -1ms) EID 18

NSOCK (0.1610s) UDP connection requested to 10.10.1.44:53 (IOD #2) EID 24

NSOCK (0.1610s) Read request from IOD #2 [10.10.1.44:53] (timeout: -1ms) EID 34

NSOCK (0.1610s) Write request for 40 bytes to IOD #1 EID 43 [10.10.1.45:53]:

V!...........1.1.10.10.in-addr.arpa.....

NSOCK (0.1610s) nsock_loop() started (timeout=500ms). 5 events pending

NSOCK (0.1610s) Callback: CONNECT SUCCESS for EID 8 [10.10.1.45:53]

NSOCK (0.1610s) Callback: CONNECT SUCCESS for EID 24 [10.10.1.44:53]

NSOCK (0.1610s) Callback: WRITE SUCCESS for EID 43 [10.10.1.45:53]

...

Packet trace output

The --packet-trace parameter is another useful tool for troubleshooting connectivity

issues. The example above displays detailed information about every packet sent to

and received from the target system.

Tip

Trace information will rapidly scroll across the screen. See page 129 for

information about saving trace data to a file for easier viewing.

144

Display Host Networking Configuration

The --iflist option displays the network interfaces and routes configured on the local

system.

Usage syntax: nmap --iflist

$ nmap --iflist

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-13 17:03 CDT

************************INTERFACES************************

DEV (SHORT) IP/MASK TYPE UP MAC

lo (lo) 127.0.0.1/8 loopback up

eth0 (eth0) 10.10.1.107/24 ethernet up 00:21:70:AC:F7:E7

wlan0 (wlan0) 10.10.1.176/24 ethernet up 00:16:EA:F0:92:50

**************************ROUTES**************************

DST/MASK DEV GATEWAY

10.10.1.0/0 eth0

10.10.1.0/0 wlan0

169.254.0.0/0 wlan0

0.0.0.0/0 eth0 10.10.1.1

Interface list output

The above example displays the general network and routing information for the

local system. This option can be helpful for quickly identifying network information

or troubleshooting connectivity issues.

Tip

Additional commands that are helpful for troubleshooting networking

configuration include ifconfig (Unix/Linux) and ipconfig (Windows). Most

Windows and Unix based systems also include the netstat command

which can provide additional network information.

145

Specify Which Network Interface to Use

The -e option is used to manually specify which network interface Nmap should use.

Usage syntax: nmap -e [interface] [target]

$ nmap -e eth0 10.10.1.48

Starting Nmap 5.00 ( http://nmap.org ) at 2009-08-25 08:30 CDT

Interesting ports on 10.10.1.48:

Not shown: 994 closed ports

PORT STATE SERVICE

21/tcp open ftp

22/tcp open ssh

25/tcp open smtp

80/tcp open http

111/tcp open rpcbind

2049/tcp open nfs

Nmap done: 1 IP address (1 host up) scanned in 0.41 seconds

Manually specifying a network interface

Many systems have multiple network interfaces. Most modern laptops, for example,

have both a regular ethernet jack and a wireless card. If you want to ensure Nmap is

using your preferred interface you can use -e to specify it on the command line. In

this example -e is used to force Nmap to scan via the eth0 interface on the multi-

homed host system.

146

147

Section 11:

Zenmap

148

Zenmap Overview

Zenmap is a graphical frontend for Nmap designed to make light work of Nmap’s

complex scanning features. The Zenmap GUI is a cross-platform program that can be

used on Windows, Mac OS X, and Unix/Linux systems.

Zenmap GUI

149

Launching Zenmap

Windows Users

Zenmap is installed by default when you install Nmap on Windows systems. To start

Zenmap go to Start > Programs > Nmap > Zenmap GUI.

Unix and Linux Users

Zenmap is automatically installed when you compile Nmap from source. If you

install Nmap via apt or yum you may have to manually install the Zenmap package.

This can be done by executing one of the following commands:

Debian/Ubuntu:

apt-get install zenmap

Fedora/Red Hat/CentOS:

yum install zenmap

Gentoo:

emerge zenmap

Once installed, the Zenmap GUI which can be launched by selecting Applications >

Internet > Zenmap from the Gnome menu.

Mac OS X Users

Zenmap for Mac OS X is installed in Applications > Zenmap. It is included

automatically as part of the default Nmap installation.

Note

The X11 server for Mac OS X is required to run Zenmap on Mac systems.

This software can be found on the Mac OS X installation DVD.

150

Basic Zenmap Operations

Performing a scan with Zenmap is as simple as 1, 2, 3...

Zenmap GUI overview

Step 1: Enter a target (or select a recent target from the list)

Step 2: Select a scanning profile

Step 3: Press the scan button

151

Zenmap Results

The results of the scan are displayed once the scan is finished. The Nmap Output

tab displays the raw output of the scan as it would appear on the command line.

Zenmap scan output

Note

The actual command line string executed is displayed in the Command

box above.

152

Scanning Profiles

Zenmap provides built-in profiles for the most common types of scans. This

simplifies the scanning process by eliminating the need to manually specify a long

string of arguments on the command line.

Zenmap scanning profiles

153

Profile Editor

If the built-in scans don’t meet your exact needs, you can create your own scan

profile. To do this, simply access the profile editor by selecting Profile > New Profile

from the Zenmap menu (or press CTRL + P on the keyboard).

Zenmap profile editor

Within the Zenmap Profile Editor, you can select the options for your custom profile

and Zenmap will automatically build the complex Nmap command line strings based

on your selections.

Once finished, simply click the Save Changes button and your custom profile will be

available for use in the profile selection menu.

154

Viewing Open Ports

Once a scan is completed you can view a user-friendly display of the results on the

Ports/Hosts tab. The buttons labeled Hosts and Services can be used to toggle the

display of the recent scans.

Zenmap ports display

155

Viewing a Network Map

After performing one or more scans, you can view the results on a graphical map on

the Topology tab.

Zenmap topology map

Zenmap’s topology feature provides an interactive graphic which can be

manipulated by pressing the Controls button to modify the various display options.

156

Saving Network Maps

You can also save a Zenmap topology map by pressing the Save Graphic button.

Saving a topology map

Zenmap supports exporting maps to several popular formats including PNG, PDF,

SVG, and Postscript.

157

Viewing Host Details

The Host Details tab provides a user-friendly display of information gathered from a

target system.

Zenmap host details

158

Viewing Scan History

The Scans tab displays scanning history for the current session.

Zenmap scan history

159

Comparing Scan Results

Nmap and Zenmap scans can be compared using the Compare Results function. To

do this, select Tools > Compare Results from the Zenmap menu or press CTRL + D.

Zenmap comparison utility

Zenmap will load recent scans into the comparison utility or you can import an

Nmap XML file (discussed on page 130) by pressing the Open button. The

differences between the two selected scans are highlighted for easy comparison.

160

Saving Scans

Zenmap scans can be saved for future reference by selecting Scan > Save Scan from

the menu or pressing CTRL + S.

Saving Zenmap scans

161

Section 12:

Nmap Scripting Engine (NSE)

162

Nmap Scripting Engine Overview

The Nmap Scripting Engine (NSE) is a powerful tool that allows users to develop

custom scripts which can be used to harness Nmap’s advanced scanning functions.

In addition to the ability to write your own custom scripts, there are also a number

of standard built-in scripts that offer some interesting features such as vulnerability

detection and exploitation. This section covers the basic usage of these built-in

scripts.

Note

Scripts for NSE are written in the Lua programming language.

Unfortunately, programming in Lua is outside the scope of this book. For

more information about Lua visit www.lua.org.

Warning

The NSE uses aggressive scanning techniques which (in some rare

cases) can cause undesirable results like system downtime and data

loss. Additionally, NSE vulnerability exploitation features could get you

into legal trouble if you don’t have permission to scan the target

systems

Summary of features covered in this section:

Feature

Option

Execute Individual Scripts

--script [script]

Execute Multiple Scripts

--script [script1,script2,etc]

Execute Scripts by Category

--script [category]

Execute Multiple Script Categories

--script [category1, category2]

Troubleshoot Scripts

--script-trace

Update the Script Database

--script-updatedb

163

Execute Individual Scripts

The --script argument is used to execute NSE scripts.

Usage syntax: nmap --script [script.nse] [target]

# nmap --script whois.nse scanme.insecure.org

Starting Nmap 5.00 ( http://nmap.org ) at 2009-11-13 15:27 CST

Interesting ports on scanme.nmap.org (64.13.134.52):

Not shown: 996 filtered ports

PORT STATE SERVICE

25/tcp closed smtp

53/tcp open domain

70/tcp closed gopher

80/tcp open http

Host script results:

| whois: Record found at whois.arin.net

| netrange: 64.13.134.0 - 64.13.134.63

| netname: NET-64-13-143-0-26

| orgname: Titan Networks

| orgid: INSEC

|_ country: US stateprov: CA

Nmap done: 1 IP address (1 host up) scanned in 8.12 seconds

Executing a NSE script

Script results are displayed under the heading “Host script results”. In the example

above, the --script option is used to execute a script called whois.nse. The built-in

whois.nse script retrieves information about the public IP address of the specified

target from ARIN (American Registry for Internet Numbers). This is just one of the

many built-in NSE scripts.

Tip

A complete list of the built-in scripts for Nmap 5.00 can be found online at

www.nmap.org/nsedoc/.

164

Execute Multiple Scripts

The Nmap Scripting Engine supports the ability to run multiple scripts concurrently.

Usage syntax: nmap --script [script1,script2,etc|"expression"] [target]

# nmap --script "smtp*" 10.10.1.44

Starting Nmap 5.00 ( http://nmap.org ) at 2009-11-15 14:24 CST

Interesting ports on 10.10.1.44:

...

| smtp-commands: EHLO exchange-01.dontfearthecommandline.com Hello

[10.10.1.173], TURN, SIZE, ETRN, PIPELINING, DSN, ENHANCEDSTATUSCODES,

8bitmime, BINARYMIME, CHUNKING, VRFY, X-EXPS GSSAPI NTLM LOGIN, X-

EXPS=LOGIN, AUTH GSSAPI NTLM LOGIN, AUTH=LOGIN, X-LINK2STATE, XEXCH50

|_ HELP This server supports the following commands: HELO EHLO

STARTTLS RCPT DATA RSET MAIL QUIT HELP AUTH TURN ETRN BDAT VRFY

|_ smtp-open-relay: OPEN RELAY found.

...

Executing all SMTP scripts

In this example, the asterisks wildcard character is used to execute all scripts that

begin with smtp. You can also provide a comma-separated list of individual scripts to

run using the following syntax: nmap --script script1,script2,script3,etc.

Note

When using wildcards, the expression must be enclosed in quotes such as

“smtp*” or “ftp*”.

Tip

Some Nmap scripts accept arguments using the --script-args option. This

allows you to specify specific parameters for a script. A complete list of

arguments for each script can be found at www.nmap.org/nsedoc/.

165

Script Categories

You can use the --script option to execute NSE scripts based on category. The table

below describes the available categories:

Nmap Cookbook The Fat Free Guide To Network Scanning

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