Security Guide Red Hat Enterprise Linux 7

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Table of Contents
⁠Chapter 1. Overview of Security Topics
⁠Chapter 2. Security Tips for Installation
⁠Chapter 3. Keeping Your System Up-to-Date
⁠Chapter 4. Hardening Your System with Tools and Services
⁠Chapter 5. System Auditing
⁠Chapter 6. Compliance and Vulnerability Scanning with OpenSCAP
⁠Chapter 7. Federal Standards and Regulations
⁠Appendix A. Encryption Standards
- ⁠A.1. Synchronous Encryption
  - ⁠A.1.1. Advanced Encryption Standard — AES
    - ⁠A.1.1.1. AES History
  - ⁠A.1.2. Data Encryption Standard — DES
    - ⁠A.1.2.1. DES History
- ⁠A.2. Public-key Encryption
⁠Appendix B. Audit System Reference
- ⁠B.1. Audit Event Fields
- ⁠B.2. Audit Record Types
⁠Appendix C. Revision History

Mirek Jahoda Robert Krátký Martin Prpič

Tomáš Čapek Stephen Wadeley Yoana Ruseva

Miroslav Svoboda

Red Hat Enterprise Linux 7

Security Guide

A Guide to Securing Red Hat Enterprise Linux 7

Red Hat Enterprise Linux 7 Security Guide

A Guide to Securing Red Hat Enterprise Linux 7

Mirek Jahoda

Red Hat Customer Content Services

mjahoda@redhat.com

Robert Krátký

Red Hat Customer Content Services

Martin Prpič

Red Hat Customer Content Services

Tomáš Čapek

Red Hat Customer Content Services

Stephen Wadeley

Red Hat Customer Content Services

Yoana Ruseva

Red Hat Customer Content Services

Miroslav Svoboda

Red Hat Customer Content Services

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Abstract

This book assists users and administrators in learning the processes and practices of

securing workstations and servers against local and remote intrusion, exploitation,

and malicious activity. Focused on Red Hat Enterprise Linux but detailing concepts

and techniques valid for all Linux systems, this guide details the planning and the

tools involved in creating a secured computing environment for the data center,

workplace, and home. With proper administrative knowledge, vigilance, and tools,

systems running Linux can be both fully functional and secured from most common

intrusion and exploit methods.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Table of Contents

⁠Chapte r 1. O verview of Security T opics

⁠1.1. What is Computer Security?

⁠1.2. Security Controls

⁠1.3. Vulnerability Assessment

⁠1.4. Security Threats

⁠1.5. Common Exploits and Attacks

⁠Chapte r 2. Security T ips f or Installation

⁠2.1. Securing BIOS

⁠2.2. Partitioning the Disk

⁠2.3. Installing the Minim um Amount of Packages Required

⁠2.4. Restricting Network Connectivity During the Installation Process

⁠2.5. Post-installation Procedures

⁠2.6. Additional Resources

⁠Chapte r 3. Kee ping Your System Up-to-Dat e

⁠3.1. Maintaining Installed Software

⁠3.2. Using the Red Hat Custom er Portal

⁠3.3. Additional Resources

⁠Chapte r 4. Hardening Your System wit h T ools and Services

⁠4.1. Desktop Security

⁠4.2. Controlling Root Access

⁠4.3. Securing Services

⁠4.4. Securing Network Access

⁠4.5. Using Firewalls

⁠4.6. Securing DNS Traffic with DNSSEC

⁠4.7. Securing Virtual Private Networks (VPNs)

⁠4.8. Using OpenSSL

⁠4.9. Using stunnel

⁠4.10. Encryption

⁠4.11. Hardening TLS Configuration

⁠4.12. Using MACsec (IEEE 802.1AE)

⁠Chapte r 5. System Auditing

⁠Use Cases

⁠5.1. Audit System Architecture

⁠5.2. Installing the audit Packages

⁠5.3. Configuring the audit Service

⁠5.4. Starting the audit Service

⁠5.5. Defining Audit Rules

⁠5.6. Understanding Audit Log Files

⁠5.7. Searching the Audit Log Files

⁠5.8. Creating Audit Reports

⁠5.9. Additional Resources

⁠Chapte r 6. Compliance and Vulne rability Scanning with O penSCAP

⁠6.1. Security Compliance in Red Hat Enterprise Linux

⁠6.2. Defining Compliance Policy

⁠6.3. Using SCAP Workbench

⁠6.4. Using oscap

⁠6.5. Using OpenSCAP with Docker

⁠6.6. Using OpenSCAP with Atomic

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T able of Contents

⁠6.7. Using OpenSCAP with Red Hat Satellite

⁠6.8. Practical Examples

⁠6.9. Additional Resources

⁠Chapte r 7. Federal Standards and Regulations

⁠7.1. Federal Information Processing Standard (FIPS)

⁠7.2. National Industrial Security Program Operating Manual (NISPOM)

⁠7.3. Paym ent Card Industry Data Security Standard (PCI DSS)

⁠7.4. Security Technical Im plementation Guide

⁠Appe ndix A. Encryption Standards

⁠A.1. Synchronous Encryption

⁠A.2. Public-key Encryption

⁠Appe ndix B. Audit System Ref e rence

⁠B.1. Audit Event Fields

⁠B.2. Audit Record Types

⁠Appe ndix C. Revision History

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Chapter 1. Overview of Security Topics

Due to the increased reliance on powerful, networked computers to help run businesses

and keep track of our personal information, entire industries have been formed around

the practice of network and computer security. Enterprises have solicited the knowledge

and skills of security experts to properly audit systems and tailor solutions to fit the

operating requirements of their organization. Because most organizations are increasingly

dynamic in nature, their workers are accessing critical company IT resources locally and

remotely, hence the need for secure computing environments has become more

pronounced.

Unfortunately, many organizations (as well as individual users) regard security as more of

an afterthought, a process that is overlooked in favor of increased power, productivity,

convenience, ease of use, and budgetary concerns. Proper security implementation is

often enacted postmortem — after an unauthorized intrusion has already occurred. Taking

the correct measures prior to connecting a site to an untrusted network, such as the

Internet, is an effective means of thwarting many attempts at intrusion.

Note

This document makes several references to files in the /lib directory. When using

64-bit systems, some of the files mentioned may instead be located in /lib64.

1.1. What is Computer Security?

Computer security is a general term that covers a wide area of computing and information

processing. Industries that depend on computer systems and networks to conduct daily

business transactions and access critical information regard their data as an important

part of their overall assets. Several terms and metrics have entered our daily business

vocabulary, such as total cost of ownership (TCO), return on investment (ROI), and quality

of service (QoS). Using these metrics, industries can calculate aspects such as data

integrity and high-availability (HA) as part of their planning and process management

costs. In some industries, such as electronic commerce, the availability and

trustworthiness of data can mean the difference between success and failure.

1.1.1. Standardizing Securit y

Enterprises in every industry rely on regulations and rules that are set by standards-

making bodies such as the American Medical Association (AMA) or the Institute of Electrical

and Electronics Engineers (IEEE). The same ideals hold true for information security. Many

security consultants and vendors agree upon the standard security model known as CIA,

or Confidentiality, Integrity, and Availability. This three-tiered model is a generally

accepted component to assessing risks of sensitive information and establishing security

policy. The following describes the CIA model in further detail:

Confidentiality — Sensitive information must be available only to a set of pre-defined

individuals. Unauthorized transmission and usage of information should be restricted.

For example, confidentiality of information ensures that a customer's personal or

financial information is not obtained by an unauthorized individual for malicious

purposes such as identity theft or credit fraud.

⁠Chapte r 1. O verview of Security T opics

Integrity — Information should not be altered in ways that render it incomplete or

incorrect. Unauthorized users should be restricted from the ability to modify or destroy

sensitive information.

Availability — Information should be accessible to authorized users any time that it is

needed. Availability is a warranty that information can be obtained with an agreed-upon

frequency and timeliness. This is often measured in terms of percentages and agreed

to formally in Service Level Agreements (SLAs) used by network service providers and

their enterprise clients.

1.2. Security Controls

Computer security is often divided into three distinct master categories, commonly

referred to as controls:

Physical

Technical

Administrative

These three broad categories define the main objectives of proper security

implementation. Within these controls are sub-categories that further detail the controls

and how to implement them.

1.2.1. Physical Controls

Physical control is the implementation of security measures in a defined structure used to

deter or prevent unauthorized access to sensitive material. Examples of physical controls

are:

Closed-circuit surveillance cameras

Motion or thermal alarm systems

Security guards

Picture IDs

Locked and dead-bolted steel doors

Biometrics (includes fingerprint, voice, face, iris, handwriting, and other automated

methods used to recognize individuals)

1.2.2. T echnical Controls

Technical controls use technology as a basis for controlling the access and usage of

sensitive data throughout a physical structure and over a network. Technical controls are

far-reaching in scope and encompass such technologies as:

Encryption

Smart cards

Network authentication

Access control lists (ACLs)

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File integrity auditing software

1.2.3. Administrat ive Controls

Administrative controls define the human factors of security. They involve all levels of

personnel within an organization and determine which users have access to what

resources and information by such means as:

Training and awareness

Disaster preparedness and recovery plans

Personnel recruitment and separation strategies

Personnel registration and accounting

1.3. Vulnerability Assessment

Given time, resources, and motivation, an attacker can break into nearly any system. All of

the security procedures and technologies currently available cannot guarantee that any

systems are completely safe from intrusion. Routers help secure gateways to the

Internet. Firewalls help secure the edge of the network. Virtual Private Networks safely

pass data in an encrypted stream. Intrusion detection systems warn you of malicious

activity. However, the success of each of these technologies is dependent upon a number

of variables, including:

The expertise of the staff responsible for configuring, monitoring, and maintaining the

technologies.

The ability to patch and update services and kernels quickly and efficiently.

The ability of those responsible to keep constant vigilance over the network.

Given the dynamic state of data systems and technologies, securing corporate resources

can be quite complex. Due to this complexity, it is often difficult to find expert resources

for all of your systems. While it is possible to have personnel knowledgeable in many

areas of information security at a high level, it is difficult to retain staff who are experts in

more than a few subject areas. This is mainly because each subject area of information

security requires constant attention and focus. Information security does not stand still.

A vulnerability assessment is an internal audit of your network and system security; the

results of which indicate the confidentiality, integrity, and availability of your network (as

explained in Section 1.1.1, “Standardizing Security”). Typically, vulnerability assessment

starts with a reconnaissance phase, during which important data regarding the target

systems and resources is gathered. This phase leads to the system readiness phase,

whereby the target is essentially checked for all known vulnerabilities. The readiness

phase culminates in the reporting phase, where the findings are classified into categories

of high, medium, and low risk; and methods for improving the security (or mitigating the

risk of vulnerability) of the target are discussed

If you were to perform a vulnerability assessment of your home, you would likely check

each door to your home to see if they are closed and locked. You would also check every

window, making sure that they closed completely and latch correctly. This same concept

applies to systems, networks, and electronic data. Malicious users are the thieves and

vandals of your data. Focus on their tools, mentality, and motivations, and you can then

react swiftly to their actions.

1.3.1. Defining Assessment and T est ing

⁠Chapte r 1. O verview of Security T opics

1.3.1. Defining Assessment and T est ing

Vulnerability assessments may be broken down into one of two types: outside looking in

and inside looking around.

When performing an outside-looking-in vulnerability assessment, you are attempting to

compromise your systems from the outside. Being external to your company provides

you with the cracker's viewpoint. You see what a cracker sees — publicly-routable IP

addresses, systems on your DMZ, external interfaces of your firewall, and more. DMZ

stands for "demilitarized zone", which corresponds to a computer or small subnetwork that

sits between a trusted internal network, such as a corporate private LAN, and an untrusted

external network, such as the public Internet. Typically, the DMZ contains devices

accessible to Internet traffic, such as Web (HTTP) servers, FTP servers, SMTP (e-mail)

servers and DNS servers.

When you perform an inside-looking-around vulnerability assessment, you are at an

advantage since you are internal and your status is elevated to trusted. This is the

viewpoint you and your co-workers have once logged on to your systems. You see print

servers, file servers, databases, and other resources.

There are striking distinctions between the two types of vulnerability assessments. Being

internal to your company gives you more privileges than an outsider. In most

organizations, security is configured to keep intruders out. Very little is done to secure

the internals of the organization (such as departmental firewalls, user-level access

controls, and authentication procedures for internal resources). Typically, there are many

more resources when looking around inside as most systems are internal to a company.

Once you are outside the company, your status is untrusted. The systems and resources

available to you externally are usually very limited.

Consider the difference between vulnerability assessments and penetration tests. Think of

a vulnerability assessment as the first step to a penetration test. The information gleaned

from the assessment is used for testing. Whereas the assessment is undertaken to

check for holes and potential vulnerabilities, the penetration testing actually attempts to

exploit the findings.

Assessing network infrastructure is a dynamic process. Security, both information and

physical, is dynamic. Performing an assessment shows an overview, which can turn up

false positives and false negatives. A false positive is a result, where the tool finds

vulnerabilities which in reality do not exist. A false negative is when it omits actual

vulnerabilities.

Security administrators are only as good as the tools they use and the knowledge they

retain. Take any of the assessment tools currently available, run them against your

system, and it is almost a guarantee that there are some false positives. Whether by

program fault or user error, the result is the same. The tool may find false positives, or,

even worse, false negatives.

Now that the difference between a vulnerability assessment and a penetration test is

defined, take the findings of the assessment and review them carefully before conducting

a penetration test as part of your new best practices approach.

Warning

Do not attempt to exploit vulnerabilities on production systems. Doing so can have

adverse effects on productivity and efficiency of your systems and network.

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The following list examines some of the benefits to performing vulnerability assessments.

Creates proactive focus on information security.

Finds potential exploits before crackers find them.

Results in systems being kept up to date and patched.

Promotes growth and aids in developing staff expertise.

Abates financial loss and negative publicity.

1.3.2. Establishing a Methodology for Vulnerability Assessment

To aid in the selection of tools for a vulnerability assessment, it is helpful to establish a

vulnerability assessment methodology. Unfortunately, there is no predefined or industry

approved methodology at this time; however, common sense and best practices can act

as a sufficient guide.

What is the target? Are we looking at one server, or are we looking at our entire network

and everything within the network? Are we external or internal to the company? The

answers to these questions are important as they help determine not only which tools to

select but also the manner in which they are used.

To learn more about establishing methodologies, see the following website:

https://www.owasp.org/ — The Open Web Application Security Project

1.3.3. Vulnerability Assessment T ools

An assessment can start by using some form of an information-gathering tool. When

assessing the entire network, map the layout first to find the hosts that are running. Once

located, examine each host individually. Focusing on these hosts requires another set of

tools. Knowing which tools to use may be the most crucial step in finding vulnerabilities.

Just as in any aspect of everyday life, there are many different tools that perform the

same job. This concept applies to performing vulnerability assessments as well. There

are tools specific to operating systems, applications, and even networks (based on the

protocols used). Some tools are free; others are not. Some tools are intuitive and easy to

use, while others are cryptic and poorly documented but have features that other tools do

not.

Finding the right tools may be a daunting task and, in the end, experience counts. If

possible, set up a test lab and try out as many tools as you can, noting the strengths and

weaknesses of each. Review the README file or man page for the tools. Additionally, look

to the Internet for more information, such as articles, step-by-step guides, or even mailing

lists specific to the tools.

The tools discussed below are just a small sampling of the available tools.

1.3.3.1. Scanning Hosts with Nmap

Nmap is a popular tool that can be used to determine the layout of a network. Nmap has

been available for many years and is probably the most often used tool when gathering

information. An excellent manual page is included that provides detailed descriptions of its

options and usage. Administrators can use Nmap on a network to find host systems and

open ports on those systems.

⁠Chapte r 1. O verview of Security T opics

Nmap is a competent first step in vulnerability assessment. You can map out all the hosts

within your network and even pass an option that allows Nmap to attempt to identify the

operating system running on a particular host. Nmap is a good foundation for establishing

a policy of using secure services and restricting unused services.

To install Nmap, run the yum install nmap command as the root user.

1.3.3.1.1. Using Nmap

Nmap can be run from a shell prompt by typing the nmap command followed by the host

name or IP address of the machine to scan:

nmap <hostname>

For example, to scan a machine with host name foo.example.com, type the following at a

shell prompt:

~]$ nmap foo.example.com

The results of a basic scan (which could take up to a few minutes, depending on where the

host is located and other network conditions) look similar to the following:

Interesting ports on foo.example.com:

Not shown: 1710 filtered ports

PORT STATE SERVICE

22/tcp open ssh

53/tcp open domain

80/tcp open http

113/tcp closed auth

Nmap tests the most common network communication ports for listening or waiting

services. This knowledge can be helpful to an administrator who wants to close

unnecessary or unused services.

For more information about using Nmap, see the official homepage at the following URL:

http://www.insecure.org/

1.3.3.2. Nessus

Nessus is a full-service security scanner. The plug-in architecture of Nessus allows users

to customize it for their systems and networks. As with any scanner, Nessus is only as

good as the signature database it relies upon. Fortunately, Nessus is frequently updated

and features full reporting, host scanning, and real-time vulnerability searches. Remember

that there could be false positives and false negatives, even in a tool as powerful and as

frequently updated as Nessus.

Note

The Nessus client and server software requires a subscription to use. It has been

included in this document as a reference to users who may be interested in using

this popular application.

Securit y Guide

For more information about Nessus, see the official website at the following URL:

http://www.nessus.org/

1.3.3.3. OpenVAS

OpenVAS (Open Vulnerability Assessment System) is a set of tools and services that can

be used to scan for vulnerabilities and for a comprehensive vulnerability management.

The OpenVAS framework offers a number of web-based, desktop, and command line

tools for controlling the various components of the solution. The core functionality of

OpenVAS is provided by a security scanner, which makes use of over 33 thousand daily-

updated Network Vulnerability Tests (NVT). Unlike Nessus (see Section 1.3.3.2, “Nessus”),

OpenVAS does not require any subscription.

For more information about OpenVAS, see the official website at the following URL:

http://www.openvas.org/

1.3.3.4. Nikto

Nikt o is an excellent common gateway interface (CGI) script scanner. Nikt o not only

checks for CGI vulnerabilities but does so in an evasive manner, so as to elude intrusion-

detection systems. It comes with thorough documentation which should be carefully

reviewed prior to running the program. If you have web servers serving CGI scripts,

Nikt o can be an excellent resource for checking the security of these servers.

More information about Nikt o can be found at the following URL:

http://cirt.net/nikto2

1.4. Security Threats

1.4.1. T hreat s to Net work Securit y

Bad practices when configuring the following aspects of a network can increase the risk of

an attack.

Insecure Architectures

A misconfigured network is a primary entry point for unauthorized users. Leaving a trust-

based, open local network vulnerable to the highly-insecure Internet is much like leaving a

door ajar in a crime-ridden neighborhood — nothing may happen for an arbitrary amount of

time, but someone exploits the opportunity eventually.

Broadcast Networks

System administrators often fail to realize the importance of networking hardware in their

security schemes. Simple hardware, such as hubs and routers, relies on the broadcast or

non-switched principle; that is, whenever a node transmits data across the network to a

recipient node, the hub or router sends a broadcast of the data packets until the recipient

node receives and processes the data. This method is the most vulnerable to address

resolution protocol (ARP) or media access control (MAC) address spoofing by both outside

intruders and unauthorized users on local hosts.

Centralized Servers

⁠Chapte r 1. O verview of Security T opics

Another potential networking pitfall is the use of centralized computing. A common cost-

cutting measure for many businesses is to consolidate all services to a single powerful

machine. This can be convenient as it is easier to manage and costs considerably less

than multiple-server configurations. However, a centralized server introduces a single

point of failure on the network. If the central server is compromised, it may render the

network completely useless or worse, prone to data manipulation or theft. In these

situations, a central server becomes an open door that allows access to the entire

network.

1.4.2. T hreat s to Server Security

Server security is as important as network security because servers often hold a great

deal of an organization's vital information. If a server is compromised, all of its contents

may become available for the cracker to steal or manipulate at will. The following sections

detail some of the main issues.

Unused Services and Open Ports

A full installation of Red Hat Enterprise Linux 7 contains more than 1000 application and

library packages. However, most server administrators do not opt to install every single

package in the distribution, preferring instead to install a base installation of packages,

including several server applications. See Section 2.3, “Installing the Minimum Amount of

Packages Required” for an explanation of the reasons to limit the number of installed

packages and for additional resources.

A common occurrence among system administrators is to install the operating system

without paying attention to what programs are actually being installed. This can be

problematic because unneeded services may be installed, configured with the default

settings, and possibly turned on. This can cause unwanted services, such as Telnet, DHCP,

or DNS, to run on a server or workstation without the administrator realizing it, which in

turn can cause unwanted traffic to the server or even a potential pathway into the system

for crackers. See Section 4.3, “Securing Services” for information on closing ports and

disabling unused services.

Unpatched Services

Most server applications that are included in a default installation are solid, thoroughly

tested pieces of software. Having been in use in production environments for many years,

their code has been thoroughly refined and many of the bugs have been found and fixed.

However, there is no such thing as perfect software and there is always room for further

refinement. Moreover, newer software is often not as rigorously tested as one might

expect, because of its recent arrival to production environments or because it may not be

as popular as other server software.

Developers and system administrators often find exploitable bugs in server applications

and publish the information on bug tracking and security-related websites such as the

Bugtraq mailing list (http://www.securityfocus.com) or the Computer Emergency Response

Team (CERT) website (http://www.cert.org). Although these mechanisms are an effective

way of alerting the community to security vulnerabilities, it is up to system administrators

to patch their systems promptly. This is particularly true because crackers have access to

these same vulnerability tracking services and will use the information to crack unpatched

systems whenever they can. Good system administration requires vigilance, constant bug

tracking, and proper system maintenance to ensure a more secure computing

environment.

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See Chapter 3, Keeping Your System Up-to-Date for more information about keeping a

system up-to-date.

Inattentive Administration

Administrators who fail to patch their systems are one of the greatest threats to server

security. According to the SysAdmin, Audit, Network, Security Institute (SANS), the primary

cause of computer security vulnerability is "assigning untrained people to maintain

security and providing neither the training nor the time to make it possible to learn and do

the job." ⁠ This applies as much to inexperienced administrators as it does to

overconfident or amotivated administrators.

Some administrators fail to patch their servers and workstations, while others fail to watch

log messages from the system kernel or network traffic. Another common error is when

default passwords or keys to services are left unchanged. For example, some databases

have default administration passwords because the database developers assume that

the system administrator changes these passwords immediately after installation. If a

database administrator fails to change this password, even an inexperienced cracker can

use a widely-known default password to gain administrative privileges to the database.

These are only a few examples of how inattentive administration can lead to

compromised servers.

Inherently Insecure Services

Even the most vigilant organization can fall victim to vulnerabilities if the network services

they choose are inherently insecure. For instance, there are many services developed

under the assumption that they are used over trusted networks; however, this

assumption fails as soon as the service becomes available over the Internet — which is

itself inherently untrusted.

One category of insecure network services are those that require unencrypted

usernames and passwords for authentication. Telnet and FTP are two such services. If

packet sniffing software is monitoring traffic between the remote user and such a service

usernames and passwords can be easily intercepted.

Inherently, such services can also more easily fall prey to what the security industry

terms the man-in-the-middle attack. In this type of attack, a cracker redirects network

traffic by tricking a cracked name server on the network to point to his machine instead of

the intended server. Once someone opens a remote session to the server, the attacker's

machine acts as an invisible conduit, sitting quietly between the remote service and the

unsuspecting user capturing information. In this way a cracker can gather administrative

passwords and raw data without the server or the user realizing it.

Another category of insecure services include network file systems and information

services such as NFS or NIS, which are developed explicitly for LAN usage but are,

unfortunately, extended to include WANs (for remote users). NFS does not, by default,

have any authentication or security mechanisms configured to prevent a cracker from

mounting the NFS share and accessing anything contained therein. NIS, as well, has vital

information that must be known by every computer on a network, including passwords and

file permissions, within a plain text ASCII or DBM (ASCII-derived) database. A cracker who

gains access to this database can then access every user account on a network, including

the administrator's account.

By default, Red Hat Enterprise Linux 7 is released with all such services turned off.

However, since administrators often find themselves forced to use these services,

careful configuration is critical. See Section 4.3, “Securing Services” for more information

about setting up services in a safe manner.

[1]

⁠Chapte r 1. O verview of Security T opics

1.4.3. T hreat s to Workst ation and Home PC Securit y

Workstations and home PCs may not be as prone to attack as networks or servers, but

since they often contain sensitive data, such as credit card information, they are targeted

by system crackers. Workstations can also be co-opted without the user's knowledge and

used by attackers as "slave" machines in coordinated attacks. For these reasons, knowing

the vulnerabilities of a workstation can save users the headache of reinstalling the

operating system, or worse, recovering from data theft.

Bad Passwords

Bad passwords are one of the easiest ways for an attacker to gain access to a system.

For more on how to avoid common pitfalls when creating a password, see Section 4.1.1,

“Password Security”.

Vulnerable Client Applications

Although an administrator may have a fully secure and patched server, that does not

mean remote users are secure when accessing it. For instance, if the server offers

Telnet or FTP services over a public network, an attacker can capture the plain text

usernames and passwords as they pass over the network, and then use the account

information to access the remote user's workstation.

Even when using secure protocols, such as SSH, a remote user may be vulnerable to

certain attacks if they do not keep their client applications updated. For instance, v.1 SSH

clients are vulnerable to an X-forwarding attack from malicious SSH servers. Once

connected to the server, the attacker can quietly capture any keystrokes and mouse

clicks made by the client over the network. This problem was fixed in the v.2 SSH protocol,

but it is up to the user to keep track of what applications have such vulnerabilities and

update them as necessary.

Section 4.1, “Desktop Security” discusses in more detail what steps administrators and

home users should take to limit the vulnerability of computer workstations.

1.5. Common Exploits and Attacks

Table 1.1, “Common Exploits” details some of the most common exploits and entry points

used by intruders to access organizational network resources. Key to these common

exploits are the explanations of how they are performed and how administrators can

properly safeguard their network against such attacks.

Table 1.1. Common Explo it s

Exploit Descript io n Not es

Securit y Guide

Null or Default

Passwords

Leaving administrative passwords

blank or using a default password

set by the product vendor. This is

most common in hardware such

as routers and firewalls, but some

services that run on Linux can

contain default administrator

passwords as well (though

Red Hat Enterprise Linux 7 does

not ship with them).

Commonly associated with

networking hardware such as

routers, firewalls, VPNs, and

network attached storage (NAS)

appliances.

Common in many legacy operating

systems, especially those that

bundle services (such as UNIX

and Windows.)

Administrators sometimes create

privileged user accounts in a rush

and leave the password null,

creating a perfect entry point for

malicious users who discover the

account.

Default Shared

Keys

Secure services sometimes

package default security keys for

development or evaluation testing

purposes. If these keys are left

unchanged and are placed in a

production environment on the

Internet, all users with the same

default keys have access to that

shared-key resource, and any

sensitive information that it

contains.

Most common in wireless access

points and preconfigured secure

server appliances.

IP Spoofing A remote machine acts as a node

on your local network, finds

vulnerabilities with your servers,

and installs a backdoor program or

Trojan horse to gain control over

your network resources.

Spoofing is quite difficult as it

involves the attacker predicting

TCP/IP sequence numbers to

coordinate a connection to target

systems, but several tools are

available to assist crackers in

performing such a vulnerability.

Depends on target system

running services (such as rsh,

telnet, FTP and others) that use

source-based authentication

techniques, which are not

recommended when compared to

PKI or other forms of encrypted

authentication used in ssh or

SSL/TLS.

Exploit Descript io n Not es

⁠Chapte r 1. O verview of Security T opics

Eavesdropping Collecting data that passes

between two active nodes on a

network by eavesdropping on the

connection between the two

nodes.

This type of attack works mostly

with plain text transmission

protocols such as Telnet, FTP, and

HTTP transfers.

Remote attacker must have

access to a compromised system

on a LAN in order to perform such

an attack; usually the cracker has

used an active attack (such as IP

spoofing or man-in-the-middle) to

compromise a system on the LAN.

Preventative measures include

services with cryptographic key

exchange, one-time passwords, or

encrypted authentication to

prevent password snooping;

strong encryption during

transmission is also advised.

Exploit Descript io n Not es

Securit y Guide

Service

Vulnerabilities

An attacker finds a flaw or

loophole in a service run over the

Internet; through this vulnerability,

the attacker compromises the

entire system and any data that it

may hold, and could possibly

compromise other systems on

the network.

HTTP-based services such as CGI

are vulnerable to remote

command execution and even

interactive shell access. Even if

the HTTP service runs as a non-

privileged user such as "nobody",

information such as configuration

files and network maps can be

read, or the attacker can start a

denial of service attack which

drains system resources or

renders it unavailable to other

users.

Services sometimes can have

vulnerabilities that go unnoticed

during development and testing;

these vulnerabilities (such as

buffer overflows, where attackers

crash a service using arbitrary

values that fill the memory buffer

of an application, giving the

attacker an interactive command

prompt from which they may

execute arbitrary commands) can

give complete administrative

control to an attacker.

Administrators should make sure

that services do not run as the

root user, and should stay vigilant

of patches and errata updates for

applications from vendors or

security organizations such as

CERT and CVE.

Exploit Descript io n Not es

⁠Chapte r 1. O verview of Security T opics

Application

Vulnerabilities

Attackers find faults in desktop

and workstation applications (such

as email clients) and execute

arbitrary code, implant Trojan

horses for future compromise, or

crash systems. Further

exploitation can occur if the

compromised workstation has

administrative privileges on the

rest of the network.

Workstations and desktops are

more prone to exploitation as

workers do not have the

expertise or experience to

prevent or detect a compromise;

it is imperative to inform

individuals of the risks they are

taking when they install

unauthorized software or open

unsolicited email attachments.

Safeguards can be implemented

such that email client software

does not automatically open or

execute attachments. Additionally,

the automatic update of

workstation software using Red

Hat Network; or other system

management services can

alleviate the burdens of multi-seat

security deployments.

Denial of

Service (DoS)

Attacks

Attacker or group of attackers

coordinate against an

organization's network or server

resources by sending

unauthorized packets to the target

host (either server, router, or

workstation). This forces the

resource to become unavailable

to legitimate users.

The most reported DoS case in

the US occurred in 2000. Several

highly-trafficked commercial and

government sites were rendered

unavailable by a coordinated ping

flood attack using several

compromised systems with high

bandwidth connections acting as

zombies, or redirected broadcast

nodes.

Source packets are usually forged

(as well as rebroadcast), making

investigation as to the true source

of the attack difficult.

Advances in ingress filtering (IETF

rfc2267) using iptables and

Network Intrusion Detection

Systems such as snort assist

administrators in tracking down

and preventing distributed DoS

attacks.

Exploit Descript io n Not es

[1] http://www.sans.org/security-resources/mistakes.php

Securit y Guide

Chapter 2. Security Tips for Installation

Security begins with the first time you put that CD or DVD into your disk drive to install

Red Hat Enterprise Linux 7. Configuring your system securely from the beginning makes it

easier to implement additional security settings later.

2.1. Securing BIOS

Password protection for the BIOS (or BIOS equivalent) and the boot loader can prevent

unauthorized users who have physical access to systems from booting using removable

media or obtaining root privileges through single user mode. The security measures you

should take to protect against such attacks depends both on the sensitivity of the

information on the workstation and the location of the machine.

For example, if a machine is used in a trade show and contains no sensitive information,

then it may not be critical to prevent such attacks. However, if an employee's laptop with

private, unencrypted SSH keys for the corporate network is left unattended at that same

trade show, it could lead to a major security breach with ramifications for the entire

company.

If the workstation is located in a place where only authorized or trusted people have

access, however, then securing the BIOS or the boot loader may not be necessary.

2.1.1. BIOS Passwords

The two primary reasons for password protecting the BIOS of a computer are ⁠ :

1. Preventing Changes to BIOS Settings — If an intruder has access to the BIOS, they

can set it to boot from a CD-ROM or a flash drive. This makes it possible for them to

enter rescue mode or single user mode, which in turn allows them to start arbitrary

processes on the system or copy sensitive data.

2. Preventing System Booting — Some BIOSes allow password protection of the boot

process. When activated, an attacker is forced to enter a password before the BIOS

launches the boot loader.

Because the methods for setting a BIOS password vary between computer

manufacturers, consult the computer's manual for specific instructions.

If you forget the BIOS password, it can either be reset with jumpers on the motherboard

or by disconnecting the CMOS battery. For this reason, it is good practice to lock the

computer case if possible. However, consult the manual for the computer or motherboard

before attempting to disconnect the CMOS battery.

2.1.1.1. Securing Non-BIOS-based Systems

Other systems and architectures use different programs to perform low-level tasks

roughly equivalent to those of the BIOS on x86 systems. For example, the Unified

Extensible Firmware Interface (UEFI) shell.

For instructions on password protecting BIOS-like programs, see the manufacturer's

instructions.

2.2. Partitioning the Disk

[2]

⁠Chapte r 2. Security T ips f or Installation

Red Hat recommends creating separate partitions for the /boot, /, /home/tmp, and

/var/tmp/ directories. The reasons for each are different, and we will address each

partition.

/boot

This partition is the first partition that is read by the system during boot up. The

boot loader and kernel images that are used to boot your system into Red Hat

Enterprise Linux 7 are stored in this partition. This partition should not be

encrypted. If this partition is included in / and that partition is encrypted or

otherwise becomes unavailable then your system will not be able to boot.

/home

When user data (/home) is stored in / instead of in a separate partition, the

partition can fill up causing the operating system to become unstable. Also, when

upgrading your system to the next version of Red Hat Enterprise Linux 7 it is a lot

easier when you can keep your data in the /home partition as it will not be

overwritten during installation. If the root partition (/) becomes corrupt your data

could be lost forever. By using a separate partition there is slightly more

protection against data loss. You can also target this partition for frequent

backups.

/tmp and /var/tmp/

Both the /tmp and /var/tmp/ directories are used to store data that does not

need to be stored for a long period of time. However, if a lot of data floods one of

these directories it can consume all of your storage space. If this happens and

these directories are stored within / then your system could become unstable

and crash. For this reason, moving these directories into their own partitions is a

good idea.

Note

During the installation process, an option to encrypt partitions is presented to you.

The user must supply a passphrase. This passphrase will be used as a key to

unlock the bulk encryption key, which is used to secure the partition's data. For more

information on LUKS, see Section 4.10.1, “Using LUKS Disk Encryption”.

2.3. Installing the Minimum Amount of Packages Required

It is best practice to install only the packages you will use because each piece of software

on your computer could possibly contain a vulnerability. If you are installing from the DVD

media, take the opportunity to select exactly what packages you want to install during the

installation. If you find you need another package, you can always add it to the system

later.

For more information about installing the Minimal install environment, see the

Software Selection chapter of the Red Hat Enterprise Linux 7 Installation Guide. A minimal

installation can also be performed by a Kickstart file using the --nobase option. For more

information about Kickstart installations, see the Package Selection section from the

Red Hat Enterprise Linux 7 Installation Guide.

Securit y Guide

2.4. Restricting Network Connectivity During the

Installation Process

When installing Red Hat Enterprise Linux, the installation medium represents a snapshot

of the system at a particular time. Because of this, it may not be up-to-date with the latest

security fixes and may be vulnerable to certain issues that were fixed only after the

system provided by the installation medium was released.

When installing a potentially vulnerable operating system, always limit exposure only to

the closest necessary network zone. The safest choice is the “no network” zone, which

means to leave your machine disconnected during the installation process. In some

cases, a LAN or intranet connection is sufficient while the Internet connection is the

riskiest. To follow the best security practices, choose the closest zone with your

repository while installing Red Hat Enterprise Linux from a network.

For more information about configuring network connectivity, see the Network & Hostname

chapter of the Red Hat Enterprise Linux 7 Installation Guide.

2.5. Post-installation Procedures

The following steps are the security-related procedures that should be performed

immediately after installation of Red Hat Enterprise Linux.

1. Update your system. enter the following command as root:

~]# yum update

2. Even though the firewall service, firewalld, is automatically enabled with the

installation of Red Hat Enterprise Linux, there are scenarios where it might be

explicitly disabled, for example in the kickstart configuration. In such a case, it is

recommended to consider re-enabling the firewall.

To start firewalld enter the following commands as root:

~]# systemctl start firewalld

~]# systemctl enable firewalld

3. To enhance security, disable services you do not need. For example, if there are

no printers installed on your computer, disable the cups service using the following

command:

~]# systemctl disable cups

To review active services, enter the following command:

~]$ systemctl list-units | grep service

2.6. Additional Resources

For more information about installation in general, see the Red Hat Enterprise Linux 7

Installation Guide.

⁠Chapte r 2. Security T ips f or Installation

[2] Since system BIOSes differ between manufacturers, som e may not support password

protection of either type, while others may support one type but not the other.

Securit y Guide

Chapter 3. Keeping Your System Up-to-Date

This chapter describes the process of keeping your system up-to-date, which involves

planning and configuring the way security updates are installed, applying changes

introduced by newly updated packages, and using the Red Hat Customer Portal for keeping

track of security advisories.

3.1. Maintaining Installed Software

As security vulnerabilities are discovered, the affected software must be updated in order

to limit any potential security risks. If the software is a part of a package within a Red Hat

Enterprise Linux distribution that is currently supported, Red Hat is committed to releasing

updated packages that fix the vulnerabilities as soon as possible.

Often, announcements about a given security exploit are accompanied with a patch (or

source code) that fixes the problem. This patch is then applied to the Red Hat

Enterprise Linux package and tested and released as an erratum update. However, if an

announcement does not include a patch, Red Hat developers first work with the maintainer

of the software to fix the problem. Once the problem is fixed, the package is tested and

released as an erratum update.

If an erratum update is released for software used on your system, it is highly

recommended that you update the affected packages as soon as possible to minimize the

amount of time the system is potentially vulnerable.

3.1.1. Planning and Configuring Securit y Updates

All software contains bugs. Often, these bugs can result in a vulnerability that can expose

your system to malicious users. Packages that have not been updated are a common

cause of computer intrusions. Implement a plan for installing security patches in a timely

manner to quickly eliminate discovered vulnerabilities, so they cannot be exploited.

Test security updates when they become available and schedule them for installation.

Additional controls need to be used to protect the system during the time between the

release of the update and its installation on the system. These controls depend on the

exact vulnerability, but may include additional firewall rules, the use of external firewalls,

or changes in software settings.

Bugs in supported packages are fixed using the errata mechanism. An erratum consists of

one or more RPM packages accompanied by a brief explanation of the problem that the

particular erratum deals with. All errata are distributed to customers with active

subscriptions through the Red Hat Subscript io n Management service. Errata that

address security issues are called Red Hat Security Advisories.

For more information on working with security errata, see Section 3.2.1, “Viewing Security

Advisories on the Customer Portal”. For detailed information about the Red Hat

Subscript ion Management service, including instructions on how to migrate from RHN

Classic, see the documentation related to this service: Red Hat Subscription Management.

3.1.1.1. Using the Security Features of Yum

The Yum package manager includes several security-related features that can be used to

search, list, display, and install security errata. These features also make it possible to

use Yum to install nothing but security updates.

⁠Chapte r 3. Kee ping Your System Up-to-Dat e

To check for security-related updates available for your system, enter the following

command as root:

~]# yum check-update --security

Loaded plugins: langpacks, product-id, subscription-manager

rhel-7-workstation-rpms/x86_64 | 3.4 kB 00:00:00

No packages needed for security; 0 packages available

Note that the above command runs in a non-interactive mode, so it can be used in scripts

for automated checking whether there are any updates available. The command returns

an exit value of 100 when there are any security updates available and 0 when there are

not. On encountering an error, it returns 1.

Analogously, use the following command to only install security-related updates:

~]# yum update --security

Use the updateinfo subcommand to display or act upon information provided by

repositories about available updates. The updateinfo subcommand itself accepts a

number of commands, some of which pertain to security-related uses. See Table 3.1,

“Security-related commands usable with yum updateinfo” for an overview of these

commands.

Table 3.1. Securit y-related commands usable wit h yum updat einf o

Command Descript io n

advisory [advisories] Displays information about one or more advisories.

Replace advisories with an advisory number or

numbers.

cves Displays the subset of information that pertains to CVE

(Common Vulnerabilities and Exposures).

security or sec Displays all security-related information.

severity [severity_level]

or sev [severity_level]

Displays information about security-relevant packages

of the supplied severity_level.

3.1.2. Updat ing and Inst alling Packages

When updating software on a system, it is important to download the update from a

trusted source. An attacker can easily rebuild a package with the same version number as

the one that is supposed to fix the problem but with a different security exploit and

release it on the Internet. If this happens, using security measures, such as verifying files

against the original RPM, does not detect the exploit. Thus, it is very important to only

download RPMs from trusted sources, such as from Red Hat, and to check the package

signatures to verify their integrity.

See the Yum chapter of the Red Hat Enterprise Linux 7 System Administrator's Guide for

detailed information on how to use the Yum package manager.

3.1.2.1. Verif ying Signed Packages

All Red Hat Enterprise Linux packages are signed with the Red Hat GPG key. GPG stands

for GNU Privacy Guard, or GnuPG, a free software package used for ensuring the

authenticity of distributed files. If the verification of a package signature fails, the package

may be altered and therefore cannot be trusted.

Securit y Guide

The Yum package manager allows for an automatic verification of all packages it installs or

upgrades. This feature is enabled by default. To configure this option on your system,

make sure the gpgcheck configuration directive is set to 1 in the /etc/yum.conf

configuration file.

Use the following command to manually verify package files on your filesystem:

rpmkeys --checksig package_file.rpm

See the Product Signing (GPG) Keys article on the Red Hat Customer Portal for additional

information about Red Hat package-signing practices.

3.1.2.2. Installing Signed Packages

To install verified packages (see Section 3.1.2.1, “Verifying Signed Packages” for

information on how to verify packages) from your filesystem, use the yum install

command as the root user as follows:

yum install package_file.rpm

Use a shell glob to install several packages at once. For example, the following commands

installs all .rpm packages in the current directory:

yum install *.rpm

Important

Before installing any security errata, be sure to read any special instructions

contained in the erratum report and execute them accordingly. See Section 3.1.3,

“Applying Changes Introduced by Installed Updates” for general instructions about

applying changes made by errata updates.

3.1.3. Applying Changes Introduced by Installed Updat es

After downloading and installing security errata and updates, it is important to halt the

usage of the old software and begin using the new software. How this is done depends on

the type of software that has been updated. The following list itemizes the general

categories of software and provides instructions for using updated versions after a

package upgrade.

Note

In general, rebooting the system is the surest way to ensure that the latest version

of a software package is used; however, this option is not always required, nor is it

always available to the system administrator.

Applicat ions

⁠Chapte r 3. Kee ping Your System Up-to-Dat e

User-space applications are any programs that can be initiated by the user.

Typically, such applications are used only when the user, a script, or an

automated task utility launch them.

Once such a user-space application is updated, halt any instances of the

application on the system, and launch the program again to use the updated

version.

Kernel

The kernel is the core software component for the Red Hat Enterprise Linux 7

operating system. It manages access to memory, the processor, and peripherals,

and it schedules all tasks.

Because of its central role, the kernel cannot be restarted without also rebooting

the computer. Therefore, an updated version of the kernel cannot be used until

the system is rebooted.

KVM

When the qemu-kvm and libvirt packages are updated, it is necessary to stop all

guest virtual machines, reload relevant virtualization modules (or reboot the host

system), and restart the virtual machines.

Use the lsmod command to determine which modules from the following are

loaded: kvm, kvm-intel, or kvm-amd. Then use the modprobe -r command to

remove and subsequently the modprobe -a command to reload the affected

modules. Fox example:

~]# lsmod | grep kvm

kvm_intel 143031 0

kvm 460181 1 kvm_intel

~]# modprobe -r kvm-intel

~]# modprobe -r kvm

~]# modprobe -a kvm kvm-intel

Shared Libraries

Shared libraries are units of code, such as glibc, that are used by a number of

applications and services. Applications utilizing a shared library typically load the

shared code when the application is initialized, so any applications using an

updated library must be halted and relaunched.

To determine which running applications link against a particular library, use the

lsof command:

lsof library

For example, to determine which running applications link against the

libwrap.so.0 library, type:

~]# lsof /lib64/libwrap.so.0

COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME

pulseaudi 12363 test mem REG 253,0 42520 34121785

/usr/lib64/libwrap.so.0.7.6

Securit y Guide

gnome-set 12365 test mem REG 253,0 42520 34121785

/usr/lib64/libwrap.so.0.7.6

gnome-she 12454 test mem REG 253,0 42520 34121785

/usr/lib64/libwrap.so.0.7.6

This command returns a list of all the running programs that use TCP wrappers for

host-access control. Therefore, any program listed must be halted and

relaunched when the tcp_wrappers package is updated.

syst emd Services

systemd services are persistent server programs usually launched during the

boot process. Examples of systemd services include sshd or vsftpd.

Because these programs usually persist in memory as long as a machine is

running, each updated systemd service must be halted and relaunched after its

package is upgraded. This can be done as the root user using the systemctl

command:

systemctl restart service_name

Replace service_name with the name of the service you want to restart, such as

sshd.

Ot her Sof t ware

Follow the instructions outlined by the resources linked below to correctly update

the following applications.

Red Hat Directory Server — See the Release Notes for the version of the

Red Hat Directory Server in question at

https://access.redhat.com/site/documentation/en-

US/Red_Hat_Directory_Server/.

Red Hat Ent erprise Virt ualizat ion Manager — See the Installation Guide

for the version of the Red Hat Enterprise Virtualization in question at

https://access.redhat.com/site/documentation/en-

US/Red_Hat_Enterprise_Virtualization/.

3.2. Using the Red Hat Customer Portal

The Red Hat Customer Portal at https://access.redhat.com/ is the main customer-oriented

resource for official information related to Red Hat products. You can use it to find

documentation, manage your subscriptions, download products and updates, open support

cases, and learn about security updates.

3.2.1. Viewing Security Advisories on the Customer Portal

To view security advisories (errata) relevant to the systems for which you have active

subscriptions, log into the Customer Portal at https://access.redhat.com/ and click on the

Download Products & Updates button on the main page. When you enter the Software

& Download Center page, continue by clicking on the Errata button to see a list of

advisories pertinent to your registered systems.

To browse a list of all security updates for all active Red Hat products, go to Securit y →

Securit y Updat es → Active Pro duct s using the navigation menu at the top of the page.

⁠Chapte r 3. Kee ping Your System Up-to-Dat e

Click on the erratum code in the left part of the table to display more detailed information

about the individual advisories. The next page contains not only a description of the given

erratum, including its causes, consequences, and required fixes, but also a list of all

packages that the particular erratum updates along with instructions on how to apply the

updates. The page also includes links to relevant references, such as related CVE.

3.2.2. Navigat ing CVE Customer Port al Pages

The CVE (Common Vulnerabilities and Exposures) project, maintained by

The MITRE Corporation, is a list of standardized names for vulnerabilities and security

exposures. To browse a list of CVE that pertain to Red Hat products on the Customer

Portal, log into your account at https://access.redhat.com/ and navigate to Securit y →

Resources → CVE Dat abase using the navigation menu at the top of the page.

Click on the CVE code in the left part of the table to display more detailed information

about the individual vulnerabilities. The next page contains not only a description of the

given CVE but also a list of affected Red Hat products along with links to relevant Red Hat

errata.

3.2.3. Underst anding Issue Severity Classification

All security issues discovered in Red Hat products are assigned an impact rating by

Red Hat Product Security according to the severity of the problem. The four-point scale

consists of the following levels: Low, Moderate, Important, and Critical. In addition to that,

every security issue is rated using the Common Vulnerability Scoring System (CVSS) base

scores.

Together, these ratings help you understand the impact of security issues, allowing you to

schedule and prioritize upgrade strategies for your systems. Note that the ratings reflect

the potential risk of a given vulnerability, which is based on a technical analysis of the bug,

not the current threat level. This means that the security impact rating does not change if

an exploit is released for a particular flaw.

To see a detailed description of the individual levels of severity ratings on the Customer

Portal, visit the Severity Ratings page.

3.3. Additional Resources

For more information about security updates, ways of applying them, the Red Hat

Customer Portal, and related topics, see the resources listed below.

Installed Document ation

yum(8) — The manual page for the Yum package manager provides information about

the way Yum can be used to install, update, and remove packages on your systems.

rpmkeys(8) — The manual page for the rpmkeys utility describes the way this program

can be used to verify the authenticity of downloaded packages.

Online Document at ion

Securit y Guide

Red Hat Enterprise Linux 7 System Administrator's Guide — The System Administrator's

Guide for Red Hat Enterprise Linux 7 documents the use of the Yum and rpm commands

that are used to install, update, and remove packages on Red Hat Enterprise Linux 7

systems.

Red Hat Enterprise Linux 7 SELinux User's and Administrator's Guide — The SELinux

User's and Administrator's Guide for Red Hat Enterprise Linux 7 documents the

configuration of the SELinux mandatory access control mechanism.

Red Hat Customer Port al

Red Hat Customer Portal, Security — The Security section of the Customer Portal

contains links to the most important resources, including the Red Hat CVE database, and

contacts for Red Hat Product Security.

Red Hat Security Blog — Articles about latest security-related issues from Red Hat

security professionals.

See Also

Chapter 2, Security Tips for Installation describes how to configure your system

securely from the beginning to make it easier to implement additional security settings

later.

Section 4.10.2, “Creating GPG Keys” describes how to create a set of personal GPG

keys to authenticate your communications.

⁠Chapte r 3. Kee ping Your System Up-to-Dat e

Chapter 4. Hardening Your System with Tools and

Services

4.1. Desktop Security

Red Hat Enterprise Linux 7 offers several ways for hardening the desktop against attacks

and preventing unauthorized accesses. This section describes recommended practices

for user passwords, session and account locking, and safe handling of removable media.

4.1.1. Password Securit y

Passwords are the primary method that Red Hat Enterprise Linux 7 uses to verify a user's

identity. This is why password security is so important for protection of the user, the

workstation, and the network.

For security purposes, the installation program configures the system to use Secure Hash

Algorithm 512 (SHA512) and shadow passwords. It is highly recommended that you do not

alter these settings.

If shadow passwords are deselected during installation, all passwords are stored as a

one-way hash in the world-readable /etc/passwd file, which makes the system vulnerable

to offline password cracking attacks. If an intruder can gain access to the machine as a

regular user, he can copy the /etc/passwd file to his own machine and run any number of

password cracking programs against it. If there is an insecure password in the file, it is

only a matter of time before the password cracker discovers it.

Shadow passwords eliminate this type of attack by storing the password hashes in the file

/etc/shadow, which is readable only by the root user.

This forces a potential attacker to attempt password cracking remotely by logging into a

network service on the machine, such as SSH or FTP. This sort of brute-force attack is

much slower and leaves an obvious trail as hundreds of failed login attempts are written

to system files. Of course, if the cracker starts an attack in the middle of the night on a

system with weak passwords, the cracker may have gained access before dawn and

edited the log files to cover his tracks.

In addition to format and storage considerations is the issue of content. The single most

important thing a user can do to protect his account against a password cracking attack is

create a strong password.

Note

Red Hat recommends using a central authentication solution, such as Red Hat

Identity Management (IdM). Using a central solution is preferred over using local

passwords. For details, see:

Introduction to Red Hat Identity Management

Defining Password Policies

4.1.1.1. Creating Strong Passwords

When creating a secure password, the user must remember that long passwords are

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stronger than short and complex ones. It is not a good idea to create a password of just

eight characters, even if it contains digits, special characters and uppercase letters.

Password cracking tools, such as John The Ripper, are optimized for breaking such

passwords, which are also hard to remember by a person.

In information theory, entropy is the level of uncertainty associated with a random variable

and is presented in bits. The higher the entropy value, the more secure the password is.

According to NIST SP 800-63-1, passwords that are not present in a dictionary comprised

of 50000 commonly selected passwords should have at least 10 bits of entropy. As such,

a password that consists of four random words contains around 40 bits of entropy. A long

password consisting of multiple words for added security is also called a passphrase, for

example:

randomword1 randomword2 randomword3 randomword4

If the system enforces the use of uppercase letters, digits, or special characters, the

passphrase that follows the above recommendation can be modified in a simple way, for

example by changing the first character to uppercase and appending "1!". Note that such

a modification does not increase the security of the passphrase significantly.

Another way to create a password yourself is using a password generator. The pwmake

is a command-line tool for generating random passwords that consist of all four groups of

characters – uppercase, lowercase, digits and special characters. The utility allows you to

specify the number of entropy bits that are used to generate the password. The entropy

is pulled from /dev/urandom. The minimum number of bits you can specify is 56, which is

enough for passwords on systems and services where brute force attacks are rare. 64

bits is adequate for applications where the attacker does not have direct access to the

password hash file. For situations when the attacker might obtain the direct access to the

password hash or the password is used as an encryption key, 80 to 128 bits should be

used. If you specify an invalid number of entropy bits, pwmake will use the default of bits.

To create a password of 128 bits, enter the following command:

pwmake 128

While there are different approaches to creating a secure password, always avoid the

following bad practices:

Using a single dictionary word, a word in a foreign language, an inverted word, or only

numbers.

Using less than 10 characters for a password or passphrase.

Using a sequence of keys from the keyboard layout.

Writing down your passwords.

Using personal information in a password, such as birth dates, anniversaries, family

member names, or pet names.

Using the same passphrase or password on multiple machines.

While creating secure passwords is imperative, managing them properly is also important,

especially for system administrators within larger organizations. The following section

details good practices for creating and managing user passwords within an organization.

4.1.1.2. Forcing Strong Passwords

⁠Chapte r 4. Hardening Your System wit h T ools and Services

If an organization has a large number of users, the system administrators have two basic

options available to force the use of strong passwords. They can create passwords for the

user, or they can let users create their own passwords while verifying the passwords are

of adequate strength.

Creating the passwords for the users ensures that the passwords are good, but it

becomes a daunting task as the organization grows. It also increases the risk of users

writing their passwords down, thus exposing them.

For these reasons, most system administrators prefer to have the users create their own

passwords, but actively verify that these passwords are strong enough. In some cases,

administrators may force users to change their passwords periodically through password

aging.

When users are asked to create or change passwords, they can use the passwd

command-line utility, which is PAM-aware (Pluggable Authentication Modules) and checks to

see if the password is too short or otherwise easy to crack. This checking is performed by

the pam_pwquality.so PAM module.

Note

In Red Hat Enterprise Linux 7, the pam_pwquality PAM module replaced

pam_cracklib, which was used in Red Hat Enterprise Linux 6 as a default module

for password quality checking. It uses the same back end as pam_cracklib.

The pam_pwquality module is used to check a password's strength against a set of rules.

Its procedure consists of two steps: first it checks if the provided password is found in a

dictionary. If not, it continues with a number of additional checks. pam_pwquality is

stacked alongside other PAM modules in the password component of the

/etc/pam.d/passwd file, and the custom set of rules is specified in the

/etc/security/pwquality.conf configuration file. For a complete list of these checks,

see the pwquality.conf (8) manual page.

Example 4.1. Conf iguring password st rengt h-checking in pwquality.conf

To enable using pam_quality, add the following line to the password stack in the

/etc/pam.d/passwd file:

password required pam_pwquality.so retry=3

Options for the checks are specified one per line. For example, to require a password

with a minimum length of 8 characters, including all four classes of characters, add the

following lines to the /etc/security/pwquality.conf file:

minlen = 8

minclass = 4

To set a password strength-check for character sequences and same consecutive

characters, add the following lines to /etc/security/pwquality.conf:

maxsequence = 3

maxrepeat = 3

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In this example, the password entered cannot contain more than 3 characters in a

monotonic sequence, such as abcd, and more than 3 identical consecutive characters,

such as 1111.

Note

As the root user is the one who enforces the rules for password creation, they can

set any password for themselves or for a regular user, despite the warning

messages.

4.1.1.3. Conf iguring Password Aging

Password aging is another technique used by system administrators to defend against

bad passwords within an organization. Password aging means that after a specified period

(usually 90 days), the user is prompted to create a new password. The theory behind this

is that if a user is forced to change his password periodically, a cracked password is only

useful to an intruder for a limited amount of time. The downside to password aging,

however, is that users are more likely to write their passwords down.

To specify password aging under Red Hat Enterprise Linux 7, make use of the chage

command.

Important

In Red Hat Enterprise Linux 7, shadow passwords are enabled by default. For more

information, see the Red Hat Enterprise Linux 7 System Administrator's Guide.

The -M option of the chage command specifies the maximum number of days the

password is valid. For example, to set a user's password to expire in 90 days, use the

following command:

chage -M 90 username

In the above command, replace username with the name of the user. To disable password

expiration, use the value of -1 after the -M option.

For more information on the options available with the chage command, see the table

below.

Table 4.1. chage command line o pt ions

Opt io n Descript io n

-d days Specifies the number of days since January 1, 1970 the

password was changed.

-E date Specifies the date on which the account is locked, in the

format YYYY-MM-DD. Instead of the date, the number of days

since January 1, 1970 can also be used.

-I days Specifies the number of inactive days after the password

expiration before locking the account. If the value is 0, the

account is not locked after the password expires.

⁠Chapte r 4. Hardening Your System wit h T ools and Services

-l Lists current account aging settings.

-m days Specify the minimum number of days after which the user

must change passwords. If the value is 0, the password does

not expire.

-M days Specify the maximum number of days for which the

password is valid. When the number of days specified by this

option plus the number of days specified with the -d option is

less than the current day, the user must change passwords

before using the account.

-W days Specifies the number of days before the password expiration

date to warn the user.

Opt io n Descript io n

You can also use the chage command in interactive mode to modify multiple password

aging and account details. Use the following command to enter interactive mode:

chage <username>

The following is a sample interactive session using this command:

~]# chage juan

Changing the aging information for juan

Enter the new value, or press ENTER for the default

Minimum Password Age [0]: 10

Maximum Password Age [99999]: 90

Last Password Change (YYYY-MM-DD) [2006-08-18]:

Password Expiration Warning [7]:

Password Inactive [-1]:

Account Expiration Date (YYYY-MM-DD) [1969-12-31]:

You can configure a password to expire the first time a user logs in. This forces users to

change passwords immediately.

1. Set up an initial password. To assign a default password, enter the following

command at a shell prompt as root:

passwd username

Warning

The passwd utility has the option to set a null password. Using a null

password, while convenient, is a highly insecure practice, as any third party

can log in and access the system using the insecure user name. Avoid using

null passwords wherever possible. If it is not possible, always make sure that

the user is ready to log in before unlocking an account with a null password.

2. Force immediate password expiration by running the following command as root:

chage -d 0 username

This command sets the value for the date the password was last changed to the

epoch (January 1, 1970). This value forces immediate password expiration no

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matter what password aging policy, if any, is in place.

Upon the initial log in, the user is now prompted for a new password.

4.1.2. Account Locking

In Red Hat Enterprise Linux 7, the pam_faillock PAM module allows system

administrators to lock out user accounts after a specified number of failed attempts.

Limiting user login attempts serves mainly as a security measure that aims to prevent

possible brute force attacks targeted to obtain a user's account password.

With the pam_faillock module, failed login attempts are stored in a separate file for each

user in the /var/run/faillock directory.

Note

The order of lines in the failed attempt log files is important. Any change in this

order can lock all user accounts, including the root user account when the

even_deny_root option is used.

Follow these steps to configure account locking:

1. To lock out any non-root user after three unsuccessful attempts and unlock that

user after 10 minutes, add two lines to the auth section of the

/etc/pam.d/system-auth and /etc/pam.d/password-auth files. After your edits,

the entire auth section in both files should look like this:

1 auth required pam_env.so

2 auth required pam_faillock.so preauth silent audit

deny=3 unlock_time=600

3 auth sufficient pam_unix.so nullok try_first_pass

4 auth [default=die] pam_faillock.so authfail audit deny=3

unlock_time=600

5 auth requisite pam_succeed_if.so uid >= 1000

quiet_success

6 auth required pam_deny.so

Lines number 2 and 4 have been added.

2. Add the following line to the account section of both files specified in the previous

step:

account required pam_faillock.so

3. To apply account locking for the root user as well, add the even_deny_root option

to the pam_faillock entries in the /etc/pam.d/system-auth and

/etc/pam.d/password-auth files:

auth required pam_faillock.so preauth silent audit

deny=3 even_deny_root unlock_time=600

auth sufficient pam_unix.so nullok try_first_pass

auth [default=die] pam_faillock.so authfail audit deny=3

⁠Chapte r 4. Hardening Your System wit h T ools and Services

even_deny_root unlock_time=600

account required pam_faillock.so

When user john attempts to log in for the fourth time after failing to log in three times

previously, his account is locked upon the fourth attempt:

[yruseva@localhost ~]$ su - john

Account locked due to 3 failed logins

su: incorrect password

To prevent the system from locking users out even after multiple failed logins, add the

following line just above the line where pam_faillock is called for the first time in both

/etc/pam.d/system-auth and /etc/pam.d/password-auth. Also replace user1, user2,

and user3 with the actual user names.

auth [success=1 default=ignore] pam_succeed_if.so user in

user1:user2:user3

To view the number of failed attempts per user, run, as root, the following command:

[root@localhost ~]# faillock

john:

When Type Source

Valid

2013-03-05 11:44:14 TTY pts/0

To unlock a user's account, run, as root, the following command:

faillock --user <username> --reset

Keeping Custom Settings with authconf ig

When modifying authentication configuration using the aut hco nf ig utility, the system-

auth and password-auth files are overwritten with the settings from the aut hconf ig

utility. This can be avoided by creating symbolic links in place of the configuration files,

which aut hconf ig recognizes and does not overwrite. In order to use custom settings in

the configuration files and aut hconf ig simultaneously, configure account locking using the

following steps:

1. Check whether the system-auth and password-auth files are already symbolic

links pointing to system-auth-ac and password-auth-ac (this is the system

default):

~]# ls -l /etc/pam.d/{password,system}-auth

If the output is similar to the following, the symbolic links are in place, and you can

skip to step number 3:

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lrwxrwxrwx. 1 root root 16 24. Feb 09.29 /etc/pam.d/password-auth

-> password-auth-ac

lrwxrwxrwx. 1 root root 28 24. Feb 09.29 /etc/pam.d/system-auth ->

system-auth-ac

If the system-auth and password-auth files are not symbolic links, continue with

the next step.

2. Rename the configuration files:

~]# mv /etc/pam.d/system-auth /etc/pam.d/system-auth-ac

~]# mv /etc/pam.d/password-auth /etc/pam.d/password-auth-ac

3. Create configuration files with your custom settings:

~]# vi /etc/pam.d/system-auth-local

The /etc/pam.d/system-auth-local file should contain the following lines:

auth required pam_faillock.so preauth silent audit

deny=3 unlock_time=600

auth include system-auth-ac

auth [default=die] pam_faillock.so authfail silent audit

deny=3 unlock_time=600

account required pam_faillock.so

account include system-auth-ac

password include system-auth-ac

session include system-auth-ac

~]# vi /etc/pam.d/password-auth-local

The /etc/pam.d/password-auth-local file should contain the following lines:

auth required pam_faillock.so preauth silent audit

deny=3 unlock_time=600

auth include password-auth-ac

auth [default=die] pam_faillock.so authfail silent audit

deny=3 unlock_time=600

account required pam_faillock.so

account include password-auth-ac

password include password-auth-ac

session include password-auth-ac

4. Create the following symbolic links:

~]# ln -sf /etc/pam.d/system-auth-local /etc/pam.d/system-auth

~]# ln -sf /etc/pam.d/password-auth-local /etc/pam.d/password-auth

⁠Chapte r 4. Hardening Your System wit h T ools and Services

For more information on various pam_faillock configuration options, see the

pam_faillock(8) manual page.

4.1.3. Session Locking

Users may need to leave their workstation unattended for a number of reasons during

everyday operation. This could present an opportunity for an attacker to physically access

the machine, especially in environments with insufficient physical security measures (see

Section 1.2.1, “Physical Controls”). Laptops are especially exposed since their mobility

interferes with physical security. You can alleviate these risks by using session locking

features which prevent access to the system until a correct password is entered.

Note

The main advantage of locking the screen instead of logging out is that a lock allows

the user's processes (such as file transfers) to continue running. Logging out would

stop these processes.

4.1.3.1. Locking Virtual Consoles Using vlock

Users may also need to lock a virtual console. This can be done using a utility called

vlock. To install this utility, execute the following command as root:

~]# yum install vlock

After installation, any console session can be locked using the vlock command without

any additional parameters. This locks the currently active virtual console session while

still allowing access to the others. To prevent access to all virtual consoles on the

workstation, execute the following:

vlock -a

In this case, vlock locks the currently active console and the -a option prevents switching

to other virtual consoles.

See the vlock(1) man page for additional information.

Important

There are several known issues relevant to the version of vlock currently available

for Red Hat Enterprise Linux 7:

The program does not currently allow unlocking consoles using the root

password. Additional information can be found in BZ#895066.

Locking a console does not clear the screen and scrollback buffer, allowing

anyone with physical access to the workstation to view previously issued

commands and any output displayed in the console. See BZ#807369 for more

information.

4.1.4. Enforcing Read-Only Mounting of Removable Media

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4.1.4. Enforcing Read-Only Mounting of Removable Media

To enforce read-only mounting of removable media (such as USB flash disks), the

administrator can use a udev rule to detect removable media and configure them to be

mounted read-only using the blo ckdev utility. This is sufficient for enforcing read-only

mounting of physical media.

Using blockdev to Force Read-Only Mounting of Removable Media

To force all removable media to be mounted read-only, create a new udev configuration

file named, for example, 80-readonly-removables.rules in the /etc/udev/rules.d/

directory with the following content:

SUBSYSTEM=="block",ATTRS{removable}=="1",RUN{program}="/sbin/blockdev --

setro %N"

The above udev rule ensures that any newly connected removable block (storage) device

is automatically configured as read-only using the blockdev utility.

Applying New udev Settings

For these settings to take effect, the new udev rules need to be applied. The udev

service automatically detects changes to its configuration files, but new settings are not

applied to already existing devices. Only newly connected devices are affected by the

new settings. Therefore, you need to unmount and unplug all connected removable media

to ensure that the new settings are applied to them when they are next plugged in.

To force udev to re-apply all rules to already existing devices, enter the following

command as root:

~# udevadm trigger

Note that forcing udev to re-apply all rules using the above command does not affect any

storage devices that are already mounted.

To force udev to reload all rules (in case the new rules are not automatically detected for

some reason), use the following command:

~# udevadm control --reload

4.2. Controlling Root Access

When administering a home machine, the user must perform some tasks as the root

user or by acquiring effective root privileges using a setuid program, such as sudo or su.

A setuid program is one that operates with the user ID (UID) of the program's owner

rather than the user operating the program. Such programs are denoted by an s in the

owner section of a long format listing, as in the following example:

~]$ ls -l /bin/su

-rwsr-xr-x. 1 root root 34904 Mar 10 2011 /bin/su

⁠Chapte r 4. Hardening Your System wit h T ools and Services

Note

The s may be upper case or lower case. If it appears as upper case, it means that

the underlying permission bit has not been set.

For the system administrator of an organization, however, choices must be made as to

how much administrative access users within the organization should have to their

machines. Through a PAM module called pam_console.so, some activities normally

reserved only for the root user, such as rebooting and mounting removable media, are

allowed for the first user that logs in at the physical console. However, other important

system administration tasks, such as altering network settings, configuring a new mouse,

or mounting network devices, are not possible without administrative privileges. As a

result, system administrators must decide how much access the users on their network

should receive.

4.2.1. Disallowing Root Access

If an administrator is uncomfortable allowing users to log in as root for these or other

reasons, the root password should be kept secret, and access to runlevel one or single

user mode should be disallowed through boot loader password protection (see

Section 4.2.5, “Securing the Boot Loader” for more information on this topic.)

The following are four different ways that an administrator can further ensure that root

logins are disallowed:

Changing the ro o t shell

To prevent users from logging in directly as root, the system administrator can

set the root account's shell to /sbin/nologin in the /etc/passwd file.

Table 4.2. Disabling t he Roo t Shell

Ef f ect s Does Not Af f ect

Prevents access to a root shell and

logs any such attempts. The following

programs are prevented from

accessing the root account:

gdm

kdm

xdm

ssh

scp

sftp

Programs that do not require a shell,

such as FTP clients, mail clients, and

many setuid programs. The following

programs are not prevented from

accessing the root account:

sudo

FTP clients

Email clients

Disabling roo t access using any co nsole device (t t y)

To further limit access to the root account, administrators can disable root logins

at the console by editing the /etc/securetty file. This file lists all devices the

root user is allowed to log into. If the file does not exist at all, the root user can

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console or a raw network interface. This is dangerous, because a user can log in

to their machine as root using Telnet, which transmits the password in plain text

over the network.

By default, Red Hat Enterprise Linux 7's /etc/securetty file only allows the root

user to log in at the console physically attached to the machine. To prevent the

root user from logging in, remove the contents of this file by typing the following

command at a shell prompt as root:

echo > /etc/securetty

To enable securetty support in the KDM, GDM, and XDM login managers, add the

following line:

auth [user_unknown=ignore success=ok ignore=ignore default=bad]

pam_securetty.so

to the files listed below:

/etc/pam.d/gdm

/etc/pam.d/gdm-autologin

/etc/pam.d/gdm-fingerprint

/etc/pam.d/gdm-password

/etc/pam.d/gdm-smartcard

/etc/pam.d/kdm

/etc/pam.d/kdm-np

/etc/pam.d/xdm

Warning

A blank /etc/securetty file does not prevent the root user from logging

in remotely using the OpenSSH suite of tools because the console is not

opened until after authentication.

Table 4.3. Disabling Roo t Lo gins

⁠Chapte r 4. Hardening Your System wit h T ools and Services

Ef f ect s Does Not Af f ect

Prevents access to the root account

using the console or the network. The

following programs are prevented

from accessing the root account:

gdm

kdm

xdm

Other network services that open a

tty

Programs that do not log in as root,

but perform administrative tasks

through setuid or other mechanisms.

The following programs are not

prevented from accessing the root

account:

sudo

ssh

scp

sftp

Disabling roo t SSH lo gins

To prevent root logins through the SSH protocol, edit the SSH daemon's

configuration file, /etc/ssh/sshd_config, and change the line that reads:

#PermitRootLogin yes

to read as follows:

PermitRootLogin no

Table 4.4. Disabling Roo t SSH Logins

Ef f ect s Does Not Af f ect

Prevents root access using the

OpenSSH suite of tools. The following

programs are prevented from

accessing the root account:

ssh

scp

sftp

Programs that are not part of the

OpenSSH suite of tools.

Using PAM t o limit root access t o services

PAM, through the /lib/security/pam_listfile.so module, allows great

flexibility in denying specific accounts. The administrator can use this module to

reference a list of users who are not allowed to log in. To limit root access to a

system service, edit the file for the target service in the /etc/pam.d/ directory

and make sure the pam_listfile.so module is required for authentication.

The following is an example of how the module is used for the vsftpd FTP server

in the /etc/pam.d/vsftpd PAM configuration file (the \ character at the end of

the first line is not necessary if the directive is on a single line):

auth required /lib/security/pam_listfile.so item=user \

sense=deny file=/etc/vsftpd.ftpusers onerr=succeed

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This instructs PAM to consult the /etc/vsftpd.ftpusers file and deny access to

the service for any listed user. The administrator can change the name of this

file, and can keep separate lists for each service or use one central list to deny

access to multiple services.

If the administrator wants to deny access to multiple services, a similar line can

be added to the PAM configuration files, such as /etc/pam.d/pop and

/etc/pam.d/imap for mail clients, or /etc/pam.d/ssh for SSH clients.

For more information about PAM, see The Linux-PAM System Administrator's Guide,

located in the /usr/share/doc/pam-<version>/html/ directory.

Table 4.5. Disabling Roo t Using PAM

Ef f ect s Does Not Af f ect

Prevents root access to network

services that are PAM aware. The

following services are prevented from

accessing the root account:

gdm

kdm

xdm

ssh

scp

sftp

FTP clients

Email clients

Any PAM aware services

Programs and services that are not

PAM aware.

4.2.2. Allowing Root Access

If the users within an organization are trusted and computer-literate, then allowing them

root access may not be an issue. Allowing root access by users means that minor

activities, like adding devices or configuring network interfaces, can be handled by the

individual users, leaving system administrators free to deal with network security and

other important issues.

On the other hand, giving root access to individual users can lead to the following issues:

Machine Misconfiguration — Users with root access can misconfigure their machines

and require assistance to resolve issues. Even worse, they might open up security

holes without knowing it.

Running Insecure Services — Users with root access might run insecure servers on

their machine, such as FTP or Telnet, potentially putting usernames and passwords at

risk. These services transmit this information over the network in plain text.

Running Email Attachments As Root — Although rare, email viruses that affect Linux do

exist. A malicious program poses the greatest threat when run by the root user.

Keeping the audit trail intact — Because the root account is often shared by multiple

users, so that multiple system administrators can maintain the system, it is impossible

to figure out which of those users was root at a given time. When using separate

logins, the account a user logs in with, as well as a unique number for session tracking

⁠Chapte r 4. Hardening Your System wit h T ools and Services

purposes, is put into the task structure, which is inherited by every process that the

user starts. When using concurrent logins, the unique number can be used to trace

actions to specific logins. When an action generates an audit event, it is recorded with

the login account and the session associated with that unique number. Use the aulast

command to view these logins and sessions. The --proof option of the aulast

command can be used suggest a specific ausearch query to isolate auditable events

generated by a particular session. For more information about the Audit system, see

Chapter 5, System Auditing.

4.2.3. Limiting Root Access

Rather than completely denying access to the root user, the administrator may want to

allow access only through setuid programs, such as su or sudo. For more information on

su and sudo, see the Gaining Privileges chapter in Red Hat Enterprise Linux 7 System

Administrator's Guide, and the su(1) and sudo(8) man pages.

4.2.4. Enabling Aut omat ic Logouts

When the user is logged in as root, an unattended login session may pose a significant

security risk. To reduce this risk, you can configure the system to automatically log out

idle users after a fixed period of time.

1. As root, add the following line at the beginning of the /etc/profile file to make

sure the processing of this file cannot be interrupted:

trap "" 1 2 3 15

2. As root, insert the following lines to the /etc/profile file to automatically log out

after 120 seconds:

export TMOUT=120

readonly TMOUT

The TMOUT variable terminates the shell if there is no activity for the specified

number of seconds (set to 120 in the above example). You can change the limit

according to the needs of the particular installation.

4.2.5. Securing t he Boot Loader

The primary reasons for password protecting a Linux boot loader are as follows:

1. Preventing Access to Single User Mode — If attackers can boot the system into

single user mode, they are logged in automatically as root without being prompted

for the root password.

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Warning

Protecting access to single user mode with a password by editing the SINGLE

parameter in the /etc/sysconfig/init file is not recommended. An attacker

can bypass the password by specifying a custom initial command (using the

init= parameter) on the kernel command line in GRUB 2. It is recommended

to password-protect the GRUB 2 boot loader, as described in the Protecting

GRUB 2 with a Password chapter in Red Hat Enterprise Linux 7 System

Administrator's Guide.

2. Preventing Access to the GRUB 2 Console — If the machine uses GRUB 2 as its boot

loader, an attacker can use the GRUB 2 editor interface to change its configuration

or to gather information using the cat command.

3. Preventing Access to Insecure Operating Systems — If it is a dual-boot system, an

attacker can select an operating system at boot time, for example DOS, which

ignores access controls and file permissions.

Red Hat Enterprise Linux 7 includes the GRUB 2 boot loader on the Intel 64 and AMD64

platform. For a detailed look at GRUB 2, see the Working With the GRUB 2 Boot Loader

chapter in Red Hat Enterprise Linux 7 System Administrator's Guide.

4.2.5.1. Disabling Interactive Startup

Pressing the I key at the beginning of the boot sequence allows you to start up your

system interactively. During an interactive startup, the system prompts you to start up

each service one by one. However, this may allow an attacker who gains physical access

to your system to disable the security-related services and gain access to the system.

To prevent users from starting up the system interactively, as root, disable the PROMPT

parameter in the /etc/sysconfig/init file:

PROMPT=no

4.2.6. Prot ect ing Hard and Symbolic Links

To prevent malicious users from exploiting potential vulnerabilities caused by unprotected

hard and symbolic links, Red Hat Enterprise Linux 7 includes a feature that only allows

links to be created or followed provided certain conditions are met.

In case of hard links, one of the following needs to be true:

The user owns the file to which they link.

The user already has read and write access to the file to which they link.

In case of symbolic links, processes are only permitted to follow links when outside of

world-writeable directories with sticky bits, or one of the following needs to be true:

The process following the symbolic link is the owner of the symbolic link.

The owner of the directory is the same as the owner of the symbolic link.

This protection is turned on by default. It is controlled by the following options in the

/usr/lib/sysctl.d/50-default.conf file:

⁠Chapte r 4. Hardening Your System wit h T ools and Services

fs.protected_hardlinks = 1

fs.protected_symlinks = 1

To override the default settings and disable the protection, create a new configuration file

called, for example, 51-no-protect-links.conf in the /etc/sysctl.d/ directory with

the following content:

fs.protected_hardlinks = 0

fs.protected_symlinks = 0

Note

Note that in order to override the default system settings, the new configuration file

needs to have the .conf extension, and it needs to be read after the default

system file (the files are read in lexicographic order, therefore settings contained in

a file with a higher number at the beginning of the file name take precedence).

See the sysctl.d(5) manual page for more detailed information about the configuration of

kernel parameters at boot using the sysctl mechanism.

4.3. Securing Services

While user access to administrative controls is an important issue for system

administrators within an organization, monitoring which network services are active is of

paramount importance to anyone who administers and operates a Linux system.

Many services under Red Hat Enterprise Linux 7 are network servers. If a network service

is running on a machine, then a server application (called a daemon), is listening for

connections on one or more network ports. Each of these servers should be treated as a

potential avenue of attack.

4.3.1. Risks T o Services

Network services can pose many risks for Linux systems. Below is a list of some of the

primary issues:

Denial of Service Attacks (DoS) — By flooding a service with requests, a denial of

service attack can render a system unusable as it tries to log and answer each

request.

Distributed Denial of Service Attack (DDoS) — A type of DoS attack which uses multiple

compromised machines (often numbering in the thousands or more) to direct a

coordinated attack on a service, flooding it with requests and making it unusable.

Script Vulnerability Attacks — If a server is using scripts to execute server-side actions,

as Web servers commonly do, an attacker can target improperly written scripts. These

script vulnerability attacks can lead to a buffer overflow condition or allow the attacker

to alter files on the system.

Buffer Overflow Attacks — Services that want to listen on ports 1 through 1023 must

start either with administrative privileges or the CAP_NET_BIND_SERVICE capability

needs to be set for them. Once a process is bound to a port and is listening on it, the

privileges or the capability are often dropped. If the privileges or the capability are not

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dropped, and the application has an exploitable buffer overflow, an attacker could gain

access to the system as the user running the daemon. Because exploitable buffer

overflows exist, crackers use automated tools to identify systems with vulnerabilities,

and once they have gained access, they use automated rootkits to maintain their

access to the system.

Note

The threat of buffer overflow vulnerabilities is mitigated in Red Hat

Enterprise Linux 7 by ExecShield, an executable memory segmentation and

protection technology supported by x86-compatible uni- and multi-processor kernels.

ExecShield reduces the risk of buffer overflow by separating virtual memory into

executable and non-executable segments. Any program code that tries to execute

outside of the executable segment (such as malicious code injected from a buffer

overflow exploit) triggers a segmentation fault and terminates.

Execshield also includes support for No eXecute (NX) technology on AMD64

platforms and Intel® 64 systems. These technologies work in conjunction with

ExecShield to prevent malicious code from running in the executable portion of

virtual memory with a granularity of 4KB of executable code, lowering the risk of

attack from buffer overflow exploits.

Important

To limit exposure to attacks over the network, all services that are unused should

be turned off.

4.3.2. Ident ifying and Configuring Services

To enhance security, most network services installed with Red Hat Enterprise Linux 7 are

turned off by default. There are, however, some notable exceptions:

cups — The default print server for Red Hat Enterprise Linux 7.

cups-lpd — An alternative print server.

xinetd — A super server that controls connections to a range of subordinate servers,

such as gssftp and telnet.

sshd — The OpenSSH server, which is a secure replacement for Telnet.

When determining whether to leave these services running, it is best to use common

sense and avoid taking any risks. For example, if a printer is not available, do not leave

cups running. The same is true for portreserve. If you do not mount NFSv3 volumes or

use NIS (the ypbind service), then rpcbind should be disabled. Checking which network

services are available to start at boot time is not sufficient. It is recommended to also

check which ports are open and listening. Refer to Section 4.4.2, “Verifying Which Ports Are

Listening” for more information.

4.3.3. Insecure Services

⁠Chapte r 4. Hardening Your System wit h T ools and Services

Potentially, any network service is insecure. This is why turning off unused services is so

important. Exploits for services are routinely revealed and patched, making it very

important to regularly update packages associated with any network service. See

Chapter 3, Keeping Your System Up-to-Date for more information.

Some network protocols are inherently more insecure than others. These include any

services that:

Transmit Usernames and Passwords Over a Network Unencrypted — Many older

protocols, such as Telnet and FTP, do not encrypt the authentication session and should

be avoided whenever possible.

Transmit Sensitive Data Over a Network Unencrypted — Many protocols transmit data

over the network unencrypted. These protocols include Telnet, FTP, HTTP, and SMTP.

Many network file systems, such as NFS and SMB, also transmit information over the

network unencrypted. It is the user's responsibility when using these protocols to limit

what type of data is transmitted.

Examples of inherently insecure services include rlogin, rsh, telnet, and vsftpd.

All remote login and shell programs (rlogin, rsh, and telnet) should be avoided in favor

of SSH. See Section 4.3.11, “Securing SSH” for more information about sshd.

FTP is not as inherently dangerous to the security of the system as remote shells, but

FTP servers must be carefully configured and monitored to avoid problems. See

Section 4.3.9, “Securing FTP” for more information about securing FTP servers.

Services that should be carefully implemented and behind a firewall include:

auth

nfs-server

smb and nbm (Samba)

yppasswdd

ypserv

ypxfrd

More information on securing network services is available in Section 4.4, “Securing

Network Access”.

4.3.4. Securing rpcbind

The rpcbind service is a dynamic port assignment daemon for RPC services such as NIS

and NFS. It has weak authentication mechanisms and has the ability to assign a wide range

of ports for the services it controls. For these reasons, it is difficult to secure.

Note

Securing rpcbind only affects NFSv2 and NFSv3 implementations, since NFSv4 no

longer requires it. If you plan to implement an NFSv2 or NFSv3 server, then rpcbind

is required, and the following section applies.

If running RPC services, follow these basic rules.

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4.3.4.1. Protect rpcbind With T CP Wrappers

It is important to use TCP Wrappers to limit which networks or hosts have access to the

rpcbind service since it has no built-in form of authentication.

Further, use only IP addresses when limiting access to the service. Avoid using host

names, as they can be forged by DNS poisoning and other methods.

4.3.4.2. Protect rpcbind With f irewalld

To further restrict access to the rpcbind service, it is a good idea to add firewalld rules

to the server and restrict access to specific networks.

Below are two example firewalld rich language commands. The first allows TCP

connections to the port 111 (used by the rpcbind service) from the 192.168.0.0/24

network. The second allows TCP connections to the same port from the localhost. All other

packets are dropped.

~]# firewall-cmd --add-rich-rule='rule family="ipv4" port port="111"

protocol="tcp" source address="192.168.0.0/24" invert="True" drop'

~]# firewall-cmd --add-rich-rule='rule family="ipv4" port port="111"

protocol="tcp" source address="127.0.0.1" accept'

To similarly limit UDP traffic, use the following command:

~]# firewall-cmd --add-rich-rule='rule family="ipv4" port port="111"

protocol="udp" source address="192.168.0.0/24" invert="True" drop'

Note

Add --permanent to the firewalld rich language commands to make the settings

permanent. See Section 4.5, “Using Firewalls” for more information about

implementing firewalls.

4.3.5. Securing rpc.mountd

The rpc.mountd daemon implements the server side of the NFS MOUNT protocol, a

protocol used by NFS version 2 (RFC 1904) and NFS version 3 (RFC 1813).

If running RPC services, follow these basic rules.

4.3.5.1. Protect rpc.mountd With T CP Wrappers

It is important to use TCP Wrappers to limit which networks or hosts have access to the

rpc.mountd service since it has no built-in form of authentication.

Further, use only IP addresses when limiting access to the service. Avoid using host

names, as they can be forged by DNS poisoning and other methods.

4.3.5.2. Protect rpc.mountd With f irewalld

To further restrict access to the rpc.mountd service, add firewalld rich language rules

to the server and restrict access to specific networks.

⁠Chapte r 4. Hardening Your System wit h T ools and Services

Below are two example firewalld rich language commands. The first allows mountd

connections from the 192.168.0.0/24 network. The second allows mountd connections

from the local host. All other packets are dropped.

~]# firewall-cmd --add-rich-rule 'rule family="ipv4" source NOT

address="192.168.0.0/24" service name="mountd" drop'

~]# firewall-cmd --add-rich-rule 'rule family="ipv4" source

address="127.0.0.1" service name="mountd" accept'

Note

Add --permanent to the firewalld rich language commands to make the settings

permanent. See Section 4.5, “Using Firewalls” for more information about

implementing firewalls.

4.3.6. Securing NIS

The Network Information Service (NIS) is an RPC service, called ypserv, which is used in

conjunction with rpcbind and other related services to distribute maps of user names,

passwords, and other sensitive information to any computer claiming to be within its

domain.

A NIS server is comprised of several applications. They include the following:

/usr/sbin/rpc.yppasswdd — Also called the yppasswdd service, this daemon allows

users to change their NIS passwords.

/usr/sbin/rpc.ypxfrd — Also called the ypxfrd service, this daemon is responsible

for NIS map transfers over the network.

/usr/sbin/ypserv — This is the NIS server daemon.

NIS is somewhat insecure by today's standards. It has no host authentication mechanisms

and transmits all of its information over the network unencrypted, including password

hashes. As a result, extreme care must be taken when setting up a network that uses

NIS. This is further complicated by the fact that the default configuration of NIS is

inherently insecure.

It is recommended that anyone planning to implement a NIS server first secure the

rpcbind service as outlined in Section 4.3.4, “Securing rpcbind”, then address the

following issues, such as network planning.

4.3.6.1. Caref ully Plan the Network

Because NIS transmits sensitive information unencrypted over the network, it is important

the service be run behind a firewall and on a segmented and secure network. Whenever

NIS information is transmitted over an insecure network, it risks being intercepted. Careful

network design can help prevent severe security breaches.

4.3.6.2. Use a Password-like NIS Domain Name and Hostname

Any machine within a NIS domain can use commands to extract information from the

server without authentication, as long as the user knows the NIS server's DNS host name

and NIS domain name.

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For instance, if someone either connects a laptop computer into the network or breaks into

the network from outside (and manages to spoof an internal IP address), the following

command reveals the /etc/passwd map:

ypcat -d <NIS_domain> -h <DNS_hostname> passwd

If this attacker is a root user, they can obtain the /etc/shadow file by typing the following

command:

ypcat -d <NIS_domain> -h <DNS_hostname> shadow

Note

If Kerberos is used, the /etc/shadow file is not stored within a NIS map.

To make access to NIS maps harder for an attacker, create a random string for the DNS

host name, such as o7hfawtgmhwg.domain.com. Similarly, create a different randomized

NIS domain name. This makes it much more difficult for an attacker to access the NIS

server.

4.3.6.3. Edit the /var/yp/securenets File

If the /var/yp/securenets file is blank or does not exist (as is the case after a default

installation), NIS listens to all networks. One of the first things to do is to put

netmask/network pairs in the file so that ypserv only responds to requests from the

appropriate network.

Below is a sample entry from a /var/yp/securenets file:

255.255.255.0 192.168.0.0

Warning

Never start a NIS server for the first time without creating the /var/yp/securenets

file.

This technique does not provide protection from an IP spoofing attack, but it does at least

place limits on what networks the NIS server services.

4.3.6.4. Assign Static Ports and Use Rich Language Rules

All of the servers related to NIS can be assigned specific ports except for rpc.yppasswdd

— the daemon that allows users to change their login passwords. Assigning ports to the

other two NIS server daemons, rpc.ypxfrd and ypserv, allows for the creation of firewall

rules to further protect the NIS server daemons from intruders.

To do this, add the following lines to /etc/sysconfig/network:

YPSERV_ARGS="-p 834"

YPXFRD_ARGS="-p 835"

⁠Chapte r 4. Hardening Your System wit h T ools and Services

The following rich language firewalld rules can then be used to enforce which network

the server listens to for these ports:

~]# firewall-cmd --add-rich-rule='rule family="ipv4" source

address="192.168.0.0/24" invert="True" port port="834-835"

protocol="tcp" drop'

~]# firewall-cmd --add-rich-rule='rule family="ipv4" source

address="192.168.0.0/24" invert="True" port port="834-835"

protocol="udp" drop'

This means that the server only allows connections to ports 834 and 835 if the requests

come from the 192.168.0.0/24 network. The first rule is for TCP and the second for UDP.

Note

See Section 4.5, “Using Firewalls” for more information about implementing firewalls

with iptables commands.

4.3.6.5. Use Kerberos Authentication

One of the issues to consider when NIS is used for authentication is that whenever a user

logs into a machine, a password hash from the /etc/shadow map is sent over the

network. If an intruder gains access to a NIS domain and sniffs network traffic, they can

collect user names and password hashes. With enough time, a password cracking program

can guess weak passwords, and an attacker can gain access to a valid account on the

network.

Since Kerberos uses secret-key cryptography, no password hashes are ever sent over

the network, making the system far more secure. See the Logging into IdM Using

Kerberos section in the Linux Domain Identity, Authentication, and Policy Guide for more

information about Kerberos.

4.3.7. Securing NFS

Important

NFS traffic can be sent using TCP in all versions, it should be used with NFSv3,

rather than UDP, and is required when using NFSv4. All versions of NFS support

Kerberos user and group authentication, as part of the RPCSEC_GSS kernel module.

Information on rpcbind is still included, since Red Hat Enterprise Linux 7 supports

NFSv3 which utilizes rpcbind.

4.3.7.1. Caref ully Plan the Network

NFSv2 and NFSv3 traditionally passed data insecurely. All versions of NFS now have the

ability to authenticate (and optionally encrypt) ordinary file system operations using

Kerberos. Under NFSv4 all operations can use Kerberos; under v2 or v3, file locking and

mounting still do not use it. When using NFSv4.0, delegations may be turned off if the

clients are behind NAT or a firewall. For information on the use of NFSv4.1 to allow

delegations to operate through NAT and firewalls, see the pNFS section of the Red Hat

Enterprise Linux 7 Storage Administration Guide.

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4.3.7.2. Securing NFS Mount Options

The use of the mount command in the /etc/fstab file is explained in the Using the mount

Command chapter of the Red Hat Enterprise Linux 7 Storage Administration Guide. From a

security administration point of view it is worthwhile to note that the NFS mount options

can also be specified in /etc/nfsmount.conf, which can be used to set custom default

options.

4.3.7.2.1. Review t he NFS Server

Warning

Only export entire file systems. Exporting a subdirectory of a file system can be a

security issue. It is possible in some cases for a client to "break out" of the

exported part of the file system and get to unexported parts (see the section on

subtree checking in the exports(5) man page.

Use the ro option to export the file system as read-only whenever possible to reduce the

number of users able to write to the mounted file system. Only use the rw option when

specifically required. See the man exports(5) page for more information. Allowing write

access increases the risk from symlink attacks for example. This includes temporary

directories such as /tmp and /usr/tmp.

Where directories must be mounted with the rw option avoid making them world-writable

whenever possible to reduce risk. Exporting home directories is also viewed as a risk as

some applications store passwords in clear text or weakly encrypted. This risk is being

reduced as application code is reviewed and improved. Some users do not set passwords

on their SSH keys so this too means home directories present a risk. Enforcing the use of

passwords or using Kerberos would mitigate that risk.

Restrict exports only to clients that need access. Use the showmount -e command on an

NFS server to review what the server is exporting. Do not export anything that is not

specifically required.

Do not use the no_root_squash option and review existing installations to make sure it is

not used. See Section 4.3.7.4, “Do Not Use the no_root_squash Option” for more

information.

The secure option is the server-side export option used to restrict exports to “reserved”

ports. By default, the server allows client communication only from “reserved” ports (ports

numbered less than 1024), because traditionally clients have only allowed “trusted” code

(such as in-kernel NFS clients) to use those ports. However, on many networks it is not

difficult for anyone to become root on some client, so it is rarely safe for the server to

assume that communication from a reserved port is privileged. Therefore the restriction

to reserved ports is of limited value; it is better to rely on Kerberos, firewalls, and

restriction of exports to particular clients.

Most clients still do use reserved ports when possible. However, reserved ports are a

limited resource, so clients (especially those with a large number of NFS mounts) may

choose to use higher-numbered ports as well. Linux clients may do this using the

“noresvport” mount option. If you want to allow this on an export, you may do so with the

“insecure” export option.

It is good practice not to allow users to login to a server. While reviewing the above

settings on an NFS server conduct a review of who and what can access the server.

⁠Chapte r 4. Hardening Your System wit h T ools and Services

4.3.7.2.2. Review t he NFS Client

Use the nosuid option to disallow the use of a set uid program. The nosuid option

disables the set-user-identifier or set-group-identifier bits. This prevents remote

users from gaining higher privileges by running a setuid program. Use this option on the

client and the server side.

The noexec option disables all executable files on the client. Use this to prevent users

from inadvertently executing files placed in the file system being shared. The nosuid and

noexec options are standard options for most, if not all, file systems.

Use the nodev option to prevent “device-files” from being processed as a hardware

device by the client.

The resvport option is a client-side mount option and secure is the corresponding

server-side export option (see explanation above). It restricts communication to a

"reserved port". The reserved or "well known" ports are reserved for privileged users

and processes such as the root user. Setting this option causes the client to use a

reserved source port to communicate with the server.

All versions of NFS now support mounting with Kerberos authentication. The mount option

to enable this is: sec=krb5.

NFSv4 supports mounting with Kerberos using krb5i for integrity and krb5p for privacy

protection. These are used when mounting with sec=krb5, but need to be configured on

the NFS server. See the man page on exports (man 5 exports) for more information.

The NFS man page (man 5 nfs) has a “SECURITY CONSIDERATIONS” section which explains

the security enhancements in NFSv4 and contains all the NFS specific mount options.

4.3.7.3. Beware of Syntax Errors

The NFS server determines which file systems to export and which hosts to export these

directories to by consulting the /etc/exports file. Be careful not to add extraneous

spaces when editing this file.

For instance, the following line in the /etc/exports file shares the directory /tmp/nfs/ to

the host bob.example.com with read/write permissions.

/tmp/nfs/ bob.example.com(rw)

The following line in the /etc/exports file, on the other hand, shares the same directory

to the host bob.example.com with read-only permissions and shares it to the world with

read/write permissions due to a single space character after the host name.

/tmp/nfs/ bob.example.com (rw)

It is good practice to check any configured NFS shares by using the showmount command

to verify what is being shared:

showmount -e <hostname>

4.3.7.4. Do Not Use the no_root_squash Option

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By default, NFS shares change the root user to the nfsnobody user, an unprivileged user

account. This changes the owner of all root-created files to nfsnobody, which prevents

uploading of programs with the setuid bit set.

If no_root_squash is used, remote root users are able to change any file on the shared

file system and leave applications infected by Trojans for other users to inadvertently

execute.

4.3.7.5. NFS Firewall Configuration

NFSv4 is the default version of NFS for Red Hat Enterprise Linux 7 and it only requires port

2049 to be open for TCP. If using NFSv3 then four additional ports are required as

explained below.

Conf iguring Port s f or NFSv3

The ports used for NFS are assigned dynamically by rpcbind, which can cause problems

when creating firewall rules. To simplify this process, use the /etc/sysconfig/nfs file to

specify which ports are to be used:

MOUNTD_PORT — TCP and UDP port for mountd (rpc.mountd)

STATD_PORT — TCP and UDP port for status (rpc.statd)

LOCKD_TCPPORT — TCP port for nlockmgr (rpc.lockd)

LOCKD_UDPPORT — UDP port nlockmgr (rpc.lockd)

Port numbers specified must not be used by any other service. Configure your firewall to

allow the port numbers specified, as well as TCP and UDP port 2049 (NFS).

Run the rpcinfo -p command on the NFS server to see which ports and RPC programs

are being used.

4.3.7.6. Secure NFS with Red Hat identity Management

Kerberos-aware NFS setup can be greatly simplified in an environment that is using

Red Hat Identity Management which is included in Red Hat Enterprise Linux.

Follow the Red Hat Enterprise Linux 7 Linux Domain Identity, Authentication, and Policy

Guide, in particular Setting up a Kerberos-aware NFS Server to learn how to secure NFS

with Kerberos when using Red Hat Identity Management.

4.3.8. Securing the Apache HT T P Server

The Apache HTTP Server is one of the most stable and secure services in Red Hat

Enterprise Linux 7. A large number of options and techniques are available to secure the

Apache HTTP Server — too numerous to delve into deeply here. The following section

briefly explains good practices when running the Apache HTTP Server.

Always verify that any scripts running on the system work as intended before putting them

into production. Also, ensure that only the root user has write permissions to any directory

containing scripts or CGIs. To do this, enter the following commands as the root user:

chown root <directory_name>

chmod 755 <directory_name>

⁠Chapte r 4. Hardening Your System wit h T ools and Services

System administrators should be careful when using the following configuration options

(configured in /etc/httpd/conf/httpd.conf):

FollowSymLinks

This directive is enabled by default, so be sure to use caution when creating

symbolic links to the document root of the Web server. For instance, it is a bad

idea to provide a symbolic link to /.

Indexes

This directive is enabled by default, but may not be desirable. To prevent visitors

from browsing files on the server, remove this directive.

UserDir

The UserDir directive is disabled by default because it can confirm the presence

of a user account on the system. To enable user directory browsing on the

server, use the following directives:

UserDir enabled

UserDir disabled root

These directives activate user directory browsing for all user directories other

than /root/. To add users to the list of disabled accounts, add a space-delimited

list of users on the UserDir disabled line.

ServerTokens

The ServerTokens directive controls the server response header field which is

sent back to clients. It includes various information which can be customized using

the following parameters:

ServerTokens Full (default option) — provides all available information (OS

type and used modules), for example:

Apache/2.0.41 (Unix) PHP/4.2.2 MyMod/1.2

ServerTokens Prod or ServerTokens ProductOnly — provides the following

information:

Apache

ServerTokens Major — provides the following information:

Apache/2

ServerTokens Minor — provides the following information:

Apache/2.0

ServerTokens Min or ServerTokens Minimal — provides the following

information:

Apache/2.0.41

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ServerTokens OS — provides the following information:

Apache/2.0.41 (Unix)

It is recommended to use the ServerTokens Prod option so that a possible

attacker does not gain any valuable information about your system.

Important

Do not remove the IncludesNoExec directive. By default, the Server-Side Includes

(SSI) module cannot execute commands. It is recommended that you do not change

this setting unless absolutely necessary, as it could, potentially, enable an attacker

to execute commands on the system.

Removing httpd Modules

In certain scenarios, it is beneficial to remove certain httpd modules to limit the

functionality of the HTTP Server. To do so, simply comment out the entire line which loads

the module you want to remove in the /etc/httpd/conf/httpd.conf file. For example, to

remove the proxy module, comment out the following line by prepending it with a hash

sign:

#LoadModule proxy_module modules/mod_proxy.so

Note that the /etc/httpd/conf.d/ directory contains configuration files which are used to

load modules as well.

httpd and SELinux

For information, see the The Apache HTTP Server and SELinux chapter from the Red Hat

Enterprise Linux 7 SELinux User's and Administrator's Guide.

4.3.9. Securing FT P

The File Transfer Protocol (FTP) is an older TCP protocol designed to transfer files over a

network. Because all transactions with the server, including user authentication, are

unencrypted, it is considered an insecure protocol and should be carefully configured.

Red Hat Enterprise Linux 7 provides two FTP servers:

Red Hat Co nt ent Accelerat o r (tux) — A kernel-space Web server with FTP

capabilities.

vsftpd — A standalone, security oriented implementation of the FTP service.

The following security guidelines are for setting up the vsftpd FTP service.

4.3.9.1. FT P Greeting Banner

Before submitting a user name and password, all users are presented with a greeting

banner. By default, this banner includes version information useful to crackers trying to

identify weaknesses in a system.

⁠Chapte r 4. Hardening Your System wit h T ools and Services

To change the greeting banner for vsftpd, add the following directive to the

/etc/vsftpd/vsftpd.conf file:

ftpd_banner=<insert_greeting_here>

Replace <insert_greeting_here> in the above directive with the text of the greeting

message.

For mutli-line banners, it is best to use a banner file. To simplify management of multiple

banners, place all banners in a new directory called /etc/banners/. The banner file for

FTP connections in this example is /etc/banners/ftp.msg. Below is an example of what

such a file may look like:

######### Hello, all activity on ftp.example.com is logged. #########

Note

It is not necessary to begin each line of the file with 220 as specified in

Section 4.4.1, “Securing Services With TCP Wrappers and xinetd”.

To reference this greeting banner file for vsftpd, add the following directive to the

/etc/vsftpd/vsftpd.conf file:

banner_file=/etc/banners/ftp.msg

It also is possible to send additional banners to incoming connections using TCP Wrappers

as described in Section 4.4.1.1, “TCP Wrappers and Connection Banners”.

4.3.9.2. Anonymous Access

The presence of the /var/ftp/ directory activates the anonymous account.

The easiest way to create this directory is to install the vsftpd package. This package

establishes a directory tree for anonymous users and configures the permissions on

directories to read-only for anonymous users.

By default the anonymous user cannot write to any directories.

Warning

If enabling anonymous access to an FTP server, be aware of where sensitive data is

stored.

4.3.9.2.1. Anonymous Uplo ad

To allow anonymous users to upload files, it is recommended that a write-only directory

be created within /var/ftp/pub/. To do this, enter the following command as root:

~]# mkdir /var/ftp/pub/upload

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Next, change the permissions so that anonymous users cannot view the contents of the

directory:

~]# chmod 730 /var/ftp/pub/upload

A long format listing of the directory should look like this:

~]# ls -ld /var/ftp/pub/upload

drwx-wx---. 2 root ftp 4096 Nov 14 22:57 /var/ftp/pub/upload

Administrators who allow anonymous users to read and write in directories often find that

their servers become a repository of stolen software.

Additionally, under vsftpd, add the following line to the /etc/vsftpd/vsftpd.conf file:

anon_upload_enable=YES

4.3.9.3. User Accounts

Because FTP transmits unencrypted user names and passwords over insecure networks

for authentication, it is a good idea to deny system users access to the server from their

user accounts.

To disable all user accounts in vsftpd, add the following directive to

/etc/vsftpd/vsftpd.conf:

local_enable=NO

4.3.9.3.1. Rest rict ing User Acco unt s

To disable FTP access for specific accounts or specific groups of accounts, such as the

root user and those with sudo privileges, the easiest way is to use a PAM list file as

described in Section 4.2.1, “Disallowing Root Access”. The PAM configuration file for vsftpd

is /etc/pam.d/vsftpd.

It is also possible to disable user accounts within each service directly.

To disable specific user accounts in vsftpd, add the user name to

/etc/vsftpd/ftpusers

4.3.9.4. Use T CP Wrappers T o Control Access

Use TCP Wrappers to control access to either FTP daemon as outlined in Section 4.4.1,

“Securing Services With TCP Wrappers and xinetd”.

4.3.10. Securing Postfix

Postfix is a Mail Transfer Agent (MTA) that uses the Simple Mail Transfer Protocol (SMTP)

to deliver electronic messages between other MTAs and to email clients or delivery

agents. Although many MTAs are capable of encrypting traffic between one another, most

do not, so sending email over any public networks is considered an inherently insecure

form of communication. Postfix replaces Sendmail as the default MTA in Red Hat

Enterprise Linux 7.

⁠Chapte r 4. Hardening Your System wit h T ools and Services

It is recommended that anyone planning to implement a Postfix server address the

following issues.

4.3.10.1. Limiting a Denial of Service Attack

Because of the nature of email, a determined attacker can flood the server with mail fairly

easily and cause a denial of service. The effectiveness of such attacks can be limited by

setting limits of the directives in the /etc/postfix/main.cf file. You can change the

value of the directives which are already there or you can add the directives you need

with the value you want in the following format:

. The following is a list of directives that can be used for limiting a denial of service attack:

smtpd_client_connection_rate_limit — The maximum number of connection

attempts any client is allowed to make to this service per time unit (described below).

The default value is 0, which means a client can make as many connections per time

unit as Postfix can accept. By default, clients in trusted networks are excluded.

anvil_rate_time_unit — This time unit is used for rate limit calculations. The default

value is 60 seconds.

smtpd_client_event_limit_exceptions — Clients that are excluded from the

connection and rate limit commands. By default, clients in trusted networks are

excluded.

smtpd_client_message_rate_limit — The maximum number of message deliveries

a client is allowed to request per time unit (regardless of whether or not Postfix

actually accepts those messages).

default_process_limit — The default maximum number of Postfix child processes

that provide a given service. This limit can be overruled for specific services in the

master.cf file. By default the value is 100.

queue_minfree — The minimum amount of free space in bytes in the queue file

system that is needed to receive mail. This is currently used by the Postfix SMTP

server to decide if it will accept any mail at all. By default, the Postfix SMTP server

rejects MAIL FROM commands when the amount of free space is less than 1.5 times

the message_size_limit. To specify a higher minimum free space limit, specify a

queue_minfree value that is at least 1.5 times the message_size_limit. By default the

queue_minfree value is 0.

header_size_limit — The maximum amount of memory in bytes for storing a

message header. If a header is larger, the excess is discarded. By default the value is

102400.

message_size_limit — The maximum size in bytes of a message, including envelope

information. By default the value is 10240000.

4.3.10.2. NFS and Postf ix

Never put the mail spool directory, /var/spool/postfix/, on an NFS shared volume.

Because NFSv2 and NFSv3 do not maintain control over user and group IDs, two or more

users can have the same UID, and receive and read each other's mail.

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Note

With NFSv4 using Kerberos, this is not the case, since the SECRPC_GSS kernel

module does not utilize UID-based authentication. However, it is still considered

good practice not to put the mail spool directory on NFS shared volumes.

4.3.10.3. Mail-only Users

To help prevent local user exploits on the Postfix server, it is best for mail users to only

access the Postfix server using an email program. Shell accounts on the mail server

should not be allowed and all user shells in the /etc/passwd file should be set to

/sbin/nologin (with the possible exception of the root user).

4.3.10.4. Disable Postf ix Network Listening

By default, Postfix is set up to only listen to the local loopback address. You can verify this

by viewing the file /etc/postfix/main.cf.

View the file /etc/postfix/main.cf to ensure that only the following inet_interfaces

line appears:

inet_interfaces = localhost

This ensures that Postfix only accepts mail messages (such as cron job reports) from the

local system and not from the network. This is the default setting and protects Postfix

from a network attack.

For removal of the localhost restriction and allowing Postfix to listen on all interfaces the

inet_interfaces = all setting can be used.

4.3.10.5. Configuring Postf ix to Use SASL

The Red Hat Enterprise Linux 7 version of Po st f ix can use the Doveco t or Cyrus SASL

implementations for SMTP Authentication (or SMTP AUTH). SMTP Authentication is an

extension of the Simple Mail Transfer Protocol. When enabled, SMTP clients are

required to authenticate to the SMTP server using an authentication method supported and

accepted by both the server and the client. This section describes how to configure

Post f ix to make use of the Do vecot SASL implementation.

To install the Doveco t POP/IMAP server, and thus make the Do vecot SASL

implementation available on your system, issue the following command as the root user:

~]# yum install dovecot

The Post f ix SMTP server can communicate with the Do vecot SASL implementation using

either a UNIX-domain socket or a TCP socket. The latter method is only needed in case the

Post f ix and Doveco t applications are running on separate machines. This guide gives

preference to the UNIX-domain socket method, which affords better privacy.

In order to instruct Po st f ix to use the Do vecot SASL implementation, a number of

configuration changes need to be performed for both applications. Follow the procedures

below to effect these changes.

⁠Chapte r 4. Hardening Your System wit h T ools and Services

Sett ing Up Doveco t

1. Modify the main Doveco t configuration file, /etc/dovecot/conf.d/10-

master.conf, to include the following lines (the default configuration file already

includes most of the relevant section, and the lines just need to be uncommented):

service auth {

unix_listener /var/spool/postfix/private/auth {

mode = 0660

user = postfix

group = postfix

}

The above example assumes the use of UNIX-domain sockets for communication

between Post f ix and Do vecot . It also assumes default settings of the Po st f ix

SMTP server, which include the mail queue located in the /var/spool/postfix/

directory, and the application running under the postfix user and group. In this

way, read and write permissions are limited to the postfix user and group.

Alternatively, you can use the following configuration to set up Dovecot to listen

for Po st f ix authentication requests through TCP:

service auth {

inet_listener {

port = 12345

}

In the above example, replace 12345 with the number of the port you want to use.

2. Edit the /etc/dovecot/conf.d/10-auth.conf configuration file to instruct

Doveco t to provide the Po st f ix SMTP server with the plain and login

authentication mechanisms:

auth_mechanisms = plain login

Sett ing Up Post f ix

In the case of Post f ix, only the main configuration file, /etc/postfix/main.cf, needs to

be modified. Add or edit the following configuration directives:

1. Enable SMTP Authentication in the Po st f ix SMTP server:

smtpd_sasl_auth_enable = yes

2. Instruct Po st f ix to use the Dovecot SASL implementation for SMTP Authentication:

smtpd_sasl_type = dovecot

3. Provide the authentication path relative to the Po st f ix queue directory (note that

the use of a relative path ensures that the configuration works regardless of

whether the Po st f ix server runs in a chroo t or not):

smtpd_sasl_path = private/auth

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This step assumes that you want to use UNIX-domain sockets for communication

between Post f ix and Do vecot . To configure Po st f ix to look for Do vecot on a

different machine in case you use TCP sockets for communication, use configuration

values similar to the following:

smtpd_sasl_path = inet:127.0.0.1:12345

In the above example, 127.0.0.1 needs to be substituted by the IP address of the

Doveco t machine and 12345 by the port specified in Doveco t 's

/etc/dovecot/conf.d/10-master.conf configuration file.

4. Specify SASL mechanisms that the Post f ix SMTP server makes available to clients.

Note that different mechanisms can be specified for encrypted and unencrypted

sessions.

smtpd_sasl_security_options = noanonymous, noplaintext

smtpd_sasl_tls_security_options = noanonymous

The above example specifies that during unencrypted sessions, no anonymous

authentication is allowed and no mechanisms that transmit unencrypted user

names or passwords are allowed. For encrypted sessions (using TLS), only non-

anonymous authentication mechanisms are allowed.

See http://www.postfix.org/SASL_README.html#smtpd_sasl_security_options for a

list of all supported policies for limiting allowed SASL mechanisms.

Addit ional Reso urces

The following online resources provide additional information useful for configuring

Post f ix SMTP Authentication through SASL.

http://wiki2.dovecot.org/HowTo/PostfixAndDovecotSASL — Contains information on how

to set up Po st f ix to use the Do vecot SASL implementation for SMTP Authentication.

http://www.postfix.org/SASL_README.html#server_sasl — Contains information on how

to set up Po st f ix to use either the Do vecot or Cyrus SASL implementations for SMTP

Authentication.

4.3.11. Securing SSH

Secure Shell (SSH) is a powerful network protocol used to communicate with another

system over a secure channel. The transmissions over SSH are encrypted and protected

from interception. See the OpenSSH chapter of the Red Hat Enterprise Linux 7 System

Administrator's Guide for general information about the SSH protocol and about using the

SSH service in Red Hat Enterprise Linux 7.

⁠Chapte r 4. Hardening Your System wit h T ools and Services

Important

This section draws attention to the most common ways of securing an SSH setup. By

no means should this list of suggested measures be considered exhaustive or

definitive. See sshd_config(5) for a description of all configuration directives

available for modifying the behavior of the sshd daemon and to ssh(1) for an

explanation of basic SSH concepts.

4.3.11.1. Cryptographic Login

SSH supports the use of cryptographic keys for logging in to computers. This is much more

secure than using only a password. If you combine this method with other authentication

methods, it can be considered a multi-factor authentication. See Section 4.3.11.2, “Multiple

Authentication Methods” for more information about using multiple authentication methods.

In order to enable the use of cryptographic keys for authentication, the

PubkeyAuthentication configuration directive in the /etc/ssh/sshd_config file needs

to be set to yes. Note that this is the default setting. Set the PasswordAuthentication

directive to no to disable the possibility of using passwords for logging in.

SSH keys can be generated using the ssh-keygen command. If invoked without additional

arguments, it creates a 2048-bit RSA key set. The keys are stored, by default, in the

~/.ssh/ directory. You can utilize the -b switch to modify the bit-strength of the key. Using

2048-bit keys is normally sufficient. The Configuring OpenSSH chapter in the Red Hat

Enterprise Linux 7 System Administrator's Guide includes detailed information about

generating key pairs.

You should see the two keys in your ~/.ssh/ directory. If you accepted the defaults when

running the ssh-keygen command, then the generated files are named id_rsa and

id_rsa.pub and contain the private and public key respectively. You should always protect

the private key from exposure by making it unreadable by anyone else but the file's

owner. The public key, however, needs to be transferred to the system you are going to

~]$ ssh-copy-id -i [user@]server

This command will also automatically append the public key to the

~/.ssh/authorized_keys file on the server. The sshd daemon will check this file when

you attempt to log in to the server.

Similarly to passwords and any other authentication mechanism, you should change your

SSH keys regularly. When you do, make sure you remove any unused keys from the

authorized_keys file.

4.3.11.2. Multiple Authentication Methods

Using multiple authentication methods, or multi-factor authentication, increases the level of

protection against unauthorized access, and as such should be considered when

hardening a system to prevent it from being compromised. Users attempting to log in to a

system that uses multi-factor authentication must successfully complete all specified

authentication methods in order to be granted access.

Use the AuthenticationMethods configuration directive in the /etc/ssh/sshd_config

file to specify which authentication methods are to be utilized. Note that it is possible to

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define more than one list of required authentication methods using this directive. If that is

the case, the user must complete every method in at least one of the lists. The lists need

to be separated by blank spaces, and the individual authentication-method names within

the lists must be comma-separated. For example:

AuthenticationMethods publickey,gssapi-with-mic publickey,keyboard-

interactive

An sshd daemon configured using the above AuthenticationMethods directive only

grants access if the user attempting to log in successfully completes either publickey

authentication followed by gssapi-with-mic or by keyboard-interactive authentication.

Note that each of the requested authentication methods needs to be explicitly enabled

using a corresponding configuration directive (such as PubkeyAuthentication) in the

/etc/ssh/sshd_config file. See the AUTHENTICATION section of ssh(1) for a general list

of available authentication methods.

4.3.11.3. Other Ways of Securing SSH

Pro t oco l Versio n

Even though the implementation of the SSH protocol supplied with Red Hat

Enterprise Linux 7 supports both the SSH-1 and SSH-2 versions of the protocol, only the

latter should be used whenever possible. The SSH-2 version contains a number of

improvements over the older SSH-1, and the majority of advanced configuration options is

only available when using SSH-2.

Users are encouraged to make use of SSH-2 in order to maximize the extent to which the

SSH protocol protects the authentication and communication for which it is used. The

version or versions of the protocol supported by the sshd daemon can be specified using

the Protocol configuration directive in the /etc/ssh/sshd_config file. The default

setting is 2.

Key Types

While the ssh-keygen command generates a pair of SSH-2 RSA keys by default, using the

-t option, it can be instructed to generate DSA or ECDSA keys as well. The ECDSA (Elliptic

Curve Digital Signature Algorithm) offers better performance at the same equivalent

symmetric key length. It also generates shorter keys.

Non-Def ault Port

By default, the sshd daemon listens on TCP port 22. Changing the port reduces the

exposure of the system to attacks based on automated network scanning, thus increasing

security through obscurity. The port can be specified using the Port directive in the

/etc/ssh/sshd_config configuration file. Note also that the default SELinux policy must

be changed to allow for the use of a non-default port. You can do this by modifying the

ssh_port_t SELinux type by typing the following command as root:

~]# semanage -a -t ssh_port_t -p tcp port_number

In the above command, replace port_number with the new port number specified using the

Port directive.

No Roo t Login

Provided that your particular use case does not require the possibility of logging in as the

⁠Chapte r 4. Hardening Your System wit h T ools and Services

root user, you should consider setting the PermitRootLogin configuration directive to no

in the /etc/ssh/sshd_config file. By disabling the possibility of logging in as the root

user, the administrator can audit which user runs what privileged command after they log

in as regular users and then gain root rights.

4.3.12. Securing PostgreSQL

PostgreSQL is an Object-Relational database management system (DBMS). In Red Hat

Enterprise Linux 7, the postgresql-server package provides Po st greSQL. If it is not

installed, enter the following command as the root user to install it:

~]# yum install postgresql-server

Before you can start using Post greSQL, you must initialize a database storage area on

disk. This is called a database cluster. To initialize a database cluster, use the command

initdb, which is installed with Po st greSQL. The desired file system location of your

database cluster is indicated by the -D option. For example:

~]$ initdb -D /home/postgresql/db1

The initdb command will attempt to create the directory you specify if it does not already

exist. We use the name /home/postgresql/db1 in this example. The /home/postgresql/db1

directory contains all the data stored in the database and also the client authentication

configuration file:

~]$ cat pg_hba.conf

# PostgreSQL Client Authentication Configuration File

# This file controls: which hosts are allowed to connect, how clients

# are authenticated, which PostgreSQL user names they can use, which

# databases they can access. Records take one of these forms:

# local DATABASE USER METHOD [OPTIONS]

# host DATABASE USER ADDRESS METHOD [OPTIONS]

# hostssl DATABASE USER ADDRESS METHOD [OPTIONS]

# hostnossl DATABASE USER ADDRESS METHOD [OPTIONS]

The following line in the pg_hba.conf file allows any authenticated local users to access

any databases with their user names:

local all all trust

This can be problematic when you use layered applications that create database users

and no local users. If you do not want to explicitly control all user names on the system,

remove this line from the pg_hba.conf file.

4.3.13. Securing Docker

Docker is an open source project that automates the deployment of applications inside

Linux Containers, and provides the capability to package an application with its runtime

dependencies into a container. To make your Do cker workflow more secure, visit Red Hat

Enterprise Linux Atomic Host 7 Container Security Guide.

4.4. Securing Network Access

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4.4.1. Securing Services With T CP Wrappers and xinetd

TCP Wrappers are capable of much more than denying access to services. This section

illustrates how they can be used to send connection banners, warn of attacks from

particular hosts, and enhance logging functionality. See the hosts_options(5) man page for

information about the TCP Wrapper functionality and control language. See the

xinetd.conf(5) man page for the available flags, which act as options you can apply to a

service.

4.4.1.1. T CP Wrappers and Connection Banners

Displaying a suitable banner when users connect to a service is a good way to let

potential attackers know that the system administrator is being vigilant. You can also

control what information about the system is presented to users. To implement a TCP

Wrappers banner for a service, use the banner option.

This example implements a banner for vsftpd. To begin, create a banner file. It can be

anywhere on the system, but it must have same name as the daemon. For this example,

the file is called /etc/banners/vsftpd and contains the following lines:

220-Hello, %c

220-All activity on ftp.example.com is logged.

220-Inappropriate use will result in your access privileges being

removed.

The %c token supplies a variety of client information, such as the user name and host

name, or the user name and IP address to make the connection even more intimidating.

For this banner to be displayed to incoming connections, add the following line to the

/etc/hosts.allow file:

vsftpd : ALL : banners /etc/banners/

4.4.1.2. T CP Wrappers and Attack Warnings

If a particular host or network has been detected attacking the server, TCP Wrappers can

be used to warn the administrator of subsequent attacks from that host or network using

the spawn directive.

In this example, assume that a cracker from the 206.182.68.0/24 network has been

detected attempting to attack the server. Place the following line in the /etc/hosts.deny

file to deny any connection attempts from that network, and to log the attempts to a

special file:

ALL : 206.182.68.0 : spawn /bin/echo `date` %c %d >>

/var/log/intruder_alert

The %d token supplies the name of the service that the attacker was trying to access.

To allow the connection and log it, place the spawn directive in the /etc/hosts.allow file.

⁠Chapte r 4. Hardening Your System wit h T ools and Services

Note

Because the spawn directive executes any shell command, it is a good idea to

create a special script to notify the administrator or execute a chain of commands in

the event that a particular client attempts to connect to the server.

4.4.1.3. T CP Wrappers and Enhanced Logging

If certain types of connections are of more concern than others, the log level can be

elevated for that service using the severity option.

For this example, assume that anyone attempting to connect to port 23 (the Telnet port)

on an FTP server is a cracker. To denote this, place an emerg flag in the log files instead

of the default flag, info, and deny the connection.

To do this, place the following line in /etc/hosts.deny:

in.telnetd : ALL : severity emerg

This uses the default authpriv logging facility, but elevates the priority from the default

value of info to emerg, which posts log messages directly to the console.

4.4.2. Verifying Which Ports Are Listening

Unnecessary open ports should be avoided because it increases the attack surface of

your system. If you find unexpected open ports in listening state after the system has

been in service, it might be a sign of intrusion, and it should be investigated.

Issue the following command as root to determine which ports are listening for

connections from the network:

~]# netstat -pan -A inet,inet6 | grep -v ESTABLISHED

Active Internet connections (servers and established)

Proto Recv-Q Send-Q Local Address Foreign Address State

PID/Program name

tcp 0 0 0.0.0.0:111 0.0.0.0:* LISTEN

1/systemd

tcp 0 0 192.168.124.1:53 0.0.0.0:* LISTEN

1975/dnsmasq

tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN

1362/sshd

tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN

1355/cupsd

tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN

1802/master

tcp6 0 0 ::1:111 :::* LISTEN

1/systemd

tcp6 0 0 :::22 :::* LISTEN

1362/sshd

tcp6 0 0 ::1:631 :::* LISTEN

1355/cupsd

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tcp6 0 0 ::1:25 :::* LISTEN

1802/master

raw6 0 0 :::58 :::* 7

791/NetworkManager

You can use the -l option of the netstat command to display only listening server

sockets:

~]# netstat -tlnw

Active Internet connections (only servers)

Proto Recv-Q Send-Q Local Address Foreign Address State

tcp 0 0 0.0.0.0:111 0.0.0.0:* LISTEN

tcp 0 0 192.168.124.1:53 0.0.0.0:* LISTEN

tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN

tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN

tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN

tcp6 0 0 ::1:111 :::* LISTEN

tcp6 0 0 :::22 :::* LISTEN

tcp6 0 0 ::1:631 :::* LISTEN

tcp6 0 0 ::1:25 :::* LISTEN

raw6 0 0 :::58 :::* 7

Note that at time of writing, the -l option does not list SCTP servers.

You can also use the ss utility for listing open ports in the listening state. But at time of

writing, this way also does not list SCTP servers.

~]# ss -tlw

Netid State Recv-Q Send-Q Local Address:Port Peer

Address:Port

udp UNCONN 0 0 :::ipv6-icmp :::*

tcp LISTEN 0 128 *:sunrpc *:*

tcp LISTEN 0 5 192.168.124.1:domain *:*

tcp LISTEN 0 128 *:ssh *:*

tcp LISTEN 0 128 127.0.0.1:ipp *:*

tcp LISTEN 0 100 127.0.0.1:smtp *:*

tcp LISTEN 0 128 ::1:sunrpc :::*

tcp LISTEN 0 128 :::ssh :::*

tcp LISTEN 0 128 ::1:ipp :::*

tcp LISTEN 0 100 ::1:smtp :::*

Review the output of the command with the services needed on the system, turn off what

is not specifically required or authorized, repeat the check. Proceed then to make external

checks using the nmap tool from another system connected through the network to the

first system. This can be used verify the rules in f irewalld.

The following is an example of the command to be issued from the console of another

system to determine which ports are listening for TCP connections from the network:

~]# nmap -sT -O 192.168.122.1

See the nmap(1) and services(5) manual pages for more information.

4.4.3. Disabling Source Routing

⁠Chapte r 4. Hardening Your System wit h T ools and Services

Source routing is an Internet Protocol mechanism that allows an IP packet to carry

information, a list of addresses, that tells a router the path the packet must take. There is

also an option to record the hops as the route is traversed. The list of hops taken, the

"route record", provides the destination with a return path to the source. This allows the

source (the sending host) to specify the route, loosely or strictly, ignoring the routing

tables of some or all of the routers. It can allow a user to redirect network traffic for

malicious purposes. Therefore, source-based routing should be disabled.

The accept_source_route option causes network interfaces to accept packets with the

Strict Source Route (SSR) or Loose Source Routing (LSR) option set. The acceptance of

source routed packets is controlled by sysctl settings. Issue the following command as

root to drop packets with the SSR or LSR option set:

~]# /sbin/sysctl -w net.ipv4.conf.all.accept_source_route=0

Disabling the forwarding of packets should also be done in conjunction with the above

when possible (disabling forwarding may interfere with virtualization). Issue the commands

listed below as root:

These commands disable forwarding of IPv4 and IPv6 packets on all interfaces.

~]# /sbin/sysctl -w net.ipv4.conf.all.forwarding=0

~]# /sbin/sysctl -w net.ipv6.conf.all.forwarding=0

These commands disable forwarding of all multicast packets on all interfaces.

~]# /sbin/sysctl -w net.ipv4.conf.all.mc_forwarding=0

~]# /sbin/sysctl -w net.ipv6.conf.all.mc_forwarding=0

Accepting ICMP redirects has few legitimate uses. Disable the acceptance and sending of

ICMP redirected packets unless specifically required.

These commands disable acceptance of all ICMP redirected packets on all interfaces.

~]# /sbin/sysctl -w net.ipv4.conf.all.accept_redirects=0

~]# /sbin/sysctl -w net.ipv6.conf.all.accept_redirects=0

This command disables acceptance of secure ICMP redirected packets on all interfaces.

~]# /sbin/sysctl -w net.ipv4.conf.all.secure_redirects=0

This command disables acceptance of all IPv4 ICMP redirected packets on all interfaces.

~]# /sbin/sysctl -w net.ipv4.conf.all.send_redirects=0

There is only a directive to disable sending of IPv4 redirected packets. See RFC4294 for

an explanation of “IPv6 Node Requirements” which resulted in this difference between

IPv4 and IPv6.

In order to make the settings permanent they must be added to /etc/sysctl.conf.

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See the sysctl man page, sysctl(8), for more information. See RFC791 for an explanation

of the Internet options related to source based routing and its variants.

Warning

Ethernet networks provide additional ways to redirect traffic, such as ARP or MAC

address spoofing, unauthorized DHCP servers, and IPv6 router or neighbor

advertisements. In addition, unicast traffic is occasionally broadcast, causing

information leaks. These weaknesses can only be addressed by specific

countermeasures implemented by the network operator. Host-based

countermeasures are not fully effective.

4.4.4. Reverse Pat h Forwarding

Reverse Path Forwarding is used to prevent packets that arrived through one interface

from leaving through a different interface. When outgoing routes and incoming routes are

different, it is sometimes referred to as asymmetric routing. Routers often route packets

this way, but most hosts should not need to do this. Exceptions are such applications that

involve sending traffic out over one link and receiving traffic over another link from a

different service provider. For example, using leased lines in combination with xDSL or

satellite links with 3G modems. If such a scenario is applicable to you, then turning off

reverse path forwarding on the incoming interface is necessary. In short, unless you know

that it is required, it is best enabled as it prevents users spoofing IP addresses from

local subnets and reduces the opportunity for DDoS attacks.

Note

Red Hat Enterprise Linux 7 defaults to using Strict Reverse Path Forwarding following

the Strict Reverse Path recommendation from RFC 3704, Ingress Filtering for

Multihomed Networks..

Warning

If forwarding is enabled, then Reverse Path Forwarding should only be disabled if

there are other means for source-address validation (such as ipt ables rules for

example).

rp_filter

Reverse Path Forwarding is enabled by means of the rp_filter directive. The

sysctl utility can be used to make changes to the running system, and

permanent changes can be made by adding lines to the /etc/sysctl.conf file.

The rp_filter option is used to direct the kernel to select from one of three

modes.

To make a temporary global change, enter the following commands as root:

sysctl -w net.ipv4.conf.default.rp_filter=integer

sysctl -w net.ipv4.conf.all.rp_filter=integer

⁠Chapte r 4. Hardening Your System wit h T ools and Services

where integer is one of the following:

0 — No source validation.

1 — Strict mode as defined in RFC 3704.

2 — Loose mode as defined in RFC 3704.

The setting can be overridden per network interface using the

net.ipv4.conf.interface.rp_filter command as follows:

sysctl -w net.ipv4.conf.interface.rp_filter=integer

To make these settings persistent across reboots, modify the /etc/sysctl.conf

file. For example, to change the mode for all interfaces, open the

/etc/sysctl.conf file with an editor running as the root user and add a line as

follows:

net.ipv4.conf.all.rp_filter=2

IPv6_rpfilter

In case of the IPv6 protocol the f irewalld daemon applies to Reverse Path

Forwarding by default. The setting can be checked in the

/etc/firewalld/firewalld.conf file. You can change the f irewalld behavior

by setting the IPv6_rpfilter option.

If you need a custom configuration of Reverse Path Forwarding, you can perform it

without the f irewalld daemon by using the ip6tables command as follows:

ip6tables -t raw -I PREROUTING -m rpfilter --invert -j DROP

This rule should be inserted near the beginning of the raw/PREROUTING chain, so

that it applies to all traffic, in particular before the stateful matching rules. For

more information about the iptables and ip6tables services, see Section 4.5.4,

“Using the iptables Service”.

4.4.4.1. Additional Resources

The following are resources which explain more about Reverse Path Forwarding.

Inst alled Do cument at ion

/usr/share/doc/kernel-doc-version/Documentation/networking/ip-sysctl.txt -

This file contains a complete list of files and options available in the

/proc/sys/net/ipv4/ directory. Before accessing the kernel documentation for the

first time, enter the following command as root:

~]# yum install kernel-doc

Online Do cument at ion

See RFC 3704 for an explanation of Ingress Filtering for Multihomed Networks.

4.5. Using Firewalls

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The firewalld daemon provides a dynamically managed firewall with support for network

“zones” to assign a level of trust to a network and its associated connections and

interfaces. It has support for IPv4 and IPv6 firewall settings. It supports Ethernet bridges

and IP set and has a separation of runtime and permanent configuration options. It also

has an interface for services or applications to add firewall rules directly. The complete

communication with firewalld is done using D-Bus.

Note

To expand your expertise, you might also be interested in the Red Hat Server

Hardening (RH413) training course.

4.5.1. Introduction to firewalld

The firewall daemon uses the restore commands of ipt ables, ip6t ables, and ebt ables

by default to speed up all firewall actions that are changing the rule set. The normal

commands are used if the configuration setting IndividualCalls is set to yes in the

firewalld.conf file or if the rules cannot be applied with the restore commands as a

fallback solution. Using the normal commands results in significant slow down.

To use the graphical f irewall-conf ig tool, press the Super key to enter the Activities

Overview, type firewall, and press Enter. The f irewall-conf ig tool appears. You will

be prompted for an administrator password.

The sidebar on the left shows the Act ive Bindings of the active zones. These are

grouped by Connect io ns, which are handled by NetworkManager, Int erf aces, and

So urces.

The f irewall-conf ig tool has a drop-down selection menu labeled Configuration. This

enables selecting between Runt ime and Permanent mode. Notice that if you select

Permanent , an additional row of icons appears in the left-hand corner. These icons only

appear in permanent configuration mode because a service's parameters cannot be

changed in Runt ime mode. This setting does not affect the Act ive Bindings sidebar.

The firewall service provided by firewalld is dynamic rather than static because

changes to the configuration can be made anytime and are immediately set live. There is

no need to save or apply the changes. No unintended disruption of existing network

connections occurs as no part of the firewall has to be reloaded.

A command-line client, f irewall-cmd, is provided. It can be used to make permanent and

non-permanent runtime changes as explained in man firewall-cmd(1). Permanent

changes need to be made as explained in the firewalld(1) man page. Note that the

firewall-cmd command can be run by the root user and also by an administrative user,

in other words, a member of the wheel group. In the latter case, the command will be

authorized through the po lkit mechanism.

The command-line client firewall-offline-cmd can only be used by the root user to

alter the permanent environment. It is not talking to firewalld, but it is using a part of the

firewalld core and the I/O backends to alter the configuration. It is not recommended to

use this tool while firewalld is active. It could be used, but changes done with the

firewall-offline-cmd are not applied immediately to firewalld. The changes are

applied to the permanent environment after firewalld was able to detect file changes in

the file system. For example, the firewall-offline-cmd command is used while

installing to set up the firewall. It can also be used in the post-installation stage to alter

the firewall configuration before the freshly installed system has been booted.

⁠Chapte r 4. Hardening Your System wit h T ools and Services

The f irewall-applet application is able to quickly launch the Net wo rkManager

configuration tab for the network connection in use. You can make changes to the assigned

firewall zone using the General tab. This applet is not installed by default in Red Hat

Enterprise Linux.

The configuration for firewalld is stored in various XML files in /usr/lib/firewalld/

and /etc/firewalld/. This allows a great deal of flexibility as the files can be edited,

written to, backed up, used as templates for other installations, and so on. The

configuration in /usr/lib/firewalld/ is the default and also the fallback configuration,

while the configuration in /etc/firewalld/ is the system specific configuration.

All applications communicate with firewalld using the D-Bus interface.

4.5.1.1. Comparison of firewalld to system-conf ig-f irewall and iptables

The essential differences between firewalld and the ipt ables (and ip6t ables)

services are:

The iptables service stores configuration in /etc/sysconfig/iptables and

/etc/sysconfig/ip6tables, while firewalld stores it in various XML files in

/usr/lib/firewalld/ and /etc/firewalld/. Note that the

/etc/sysconfig/iptables file does not exist as firewalld is installed by default on

Red Hat Enterprise Linux.

With the ipt ables service, every single change means flushing all the old rules and

reading all the new rules from /etc/sysconfig/iptables, while with firewalld there

is no recreating of all the rules. Only the differences are applied. Consequently,

firewalld can change the settings during runtime without existing connections being

lost.

Both use ipt ables t o o l to talk to the kernel packet filter.

Note

⁠firewalld is not able to import firewall settings from the

/etc/sysconfig/ip*tables files. To import lokkit or syst em-conf ig-f irewall

settings, use the f irewall-of f line-cmd and the /etc/sysconfig/system-config-

firewall file. Custom rules files cannot be imported to ⁠firewalld. The imported

settings are applied to the default zone.

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Figure 4.1. T he Firewall St ack

4.5.1.2. Understanding Network Zones

firewalld can be used to separate networks into different zones based on the level of

trust the user has decided to place on the interfaces and traffic within that network.

Net workManager informs firewalld to which zone an interface belongs. An interface's

assigned zone can be changed by Net workManager or via the f irewall-conf ig tool,

which can open the relevant Net workManager window for you. You can also use the

firewall-cmd command-line tool. If an interface is controlled by Net workManager and

the user changes the zone of the interface using firewall-cmd, firewall-offline-cmd,

or f irewall-co nf ig, then this request is forwarded to Net workManager and is not

handled by ⁠firewalld.

The zone settings in /etc/firewalld/ are a range of preset settings, which can be

quickly applied to a network interface. They are listed below with a brief explanation.

drop

Any incoming network packets are dropped; there is no reply. Only outgoing

network connections are possible.

⁠Chapte r 4. Hardening Your System wit h T ools and Services

block

Any incoming network connections are rejected with an icmp-host-prohibited

message for IPv4 and icmp6-adm-prohibited for IPv6. Only network connections

initiated from within the system are possible.

public

For use in public areas. You do not trust the other computers on the network to

not harm your computer. Only selected incoming connections are accepted.

external

For use on external networks with masquerading enabled, especially for routers.

You do not trust the other computers on the network to not harm your computer.

Only selected incoming connections are accepted.

dmz

For computers in your demilitarized zone that are publicly-accessible with limited

access to your internal network. Only selected incoming connections are

accepted.

work

For use in work areas. You mostly trust the other computers on networks to not

harm your computer. Only selected incoming connections are accepted.

home

For use in home areas. You mostly trust the other computers on networks to not

harm your computer. Only selected incoming connections are accepted.

internal

For use on internal networks. You mostly trust the other computers on the

networks to not harm your computer. Only selected incoming connections are

accepted.

trusted

All network connections are accepted.

It is possible to designate one of these zones to be the default zone. When interface

connections are added to Net workManager, they are assigned to the default zone. On

installation, the default zone in firewalld is set to be the public zone.

Cho o sing a Net work Zo ne

The network zone names have been chosen to be self-explanatory and to allow users to

quickly make a reasonable decision. A review of the default configuration settings should

be made and unnecessary services disabled according to your needs and risk

assessments.

The zone names and settings are proposals and can be changed according to the needs.

A built-in zone cannot be removed, but it is possible to revert the zone configuration back

to the initial defaults by loading the zone defaults either in the permanent configuration of

f irewall-co nf ig or firewall-cmd.

4.5.1.3. Understanding Predef ined Services

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A service can be a list of local ports, protocols, source ports, and destinations as well as a

list of firewall helper modules automatically loaded if a service is enabled. The use of

predefined services makes it easier for the user to enable and disable access to a

service. Using the predefined services or custom-defined services, as opposed to

opening ports or ranges of ports, may make administration easier. Service configuration

options and generic file information are described in the firewalld.service(5) man

page. The services are specified by means of individual XML configuration files, which are

named in the following format: service-name.xml. Protocol names are preferred over

service or application names in firewalld.

To view the list of services using the graphical f irewall-conf ig tool, press the Super key

to enter the Activities Overview, type firewall, and press Enter. The f irewall-conf ig

tool appears. You will be prompted for an administrator password. You can now view the

list of services under the Services tab.

To list all services available on the system, enter the following command:

~]$ firewall-cmd --get-services

To get the settings of a service, use the following command:

~]$ firewall-cmd --info-service=service-name

To list only the default predefined services available using the command-line, enter the

following command:

~]$ ls /usr/lib/firewalld/services/

Note

The root user is not needed to list files in /usr/lib/firewalld. Make sure to

change the attributes accordingly after an addition of custom private files.

Files in /usr/lib/firewalld/services/ must not be edited. Only the files in

/etc/firewalld/services/ should be edited.

To list the system or user-created services, enter the following command as root:

~]# ls /etc/firewalld/services/

Services can be added and removed using the graphical f irewall-conf ig tool, firewall-

cmd, and firewall-offline-cmd. Alternatively, you can edit the XML files in

/etc/firewalld/services/. If a service has not been added or changed by the user,

then no corresponding XML file will be found in /etc/firewalld/services/. The files

/usr/lib/firewalld/services/ can be used as templates if you want to add or change

a service.

To add a new service in a terminal, use firewall-cmd, or firewall-offline-cmd in case

of not active firewalld. enter the following command to add a new and empty service:

~]$ firewall-cmd --permanent --new-service=service-name

To add a new service using a local file, use the following command:

⁠Chapte r 4. Hardening Your System wit h T ools and Services

~]$ firewall-cmd --permanent --new-service-from-file=service-name.xml

You can change the service name with the additional --name=service-name option.

As soon as service settings are changed, an updated copy of the service is placed into

/etc/firewalld/services/.

As root, you can enter the following command to copy a service manually:

~]# cp /usr/lib/firewalld/services/service-name.xml

/etc/firewalld/services/service-name.xml

firewalld loads files from /usr/lib/firewalld/services in the first place. If files are

placed in /etc/firewalld/services and they are valid, then these will override the

matching files from /usr/lib/firewalld/services. The overriden files in

/usr/lib/firewalld/services will be used as soon as the matching files in

/etc/firewalld/services have been removed or if firewalld has been asked to load

the defaults of the services. This applies to the permanent environment only. A reload is

needed to get these fallbacks also in the runtime environment.

4.5.1.4. Understanding the Direct Interf ace

firewalld has direct interface, which enables directly passing rules to ipt ables,

ip6t ables and ebt ables. It is primarily intended for use by applications. It is not

recommended and it is dangerous to use the direct interface if you are not very familiar

with ipt ables, as you could inadvertently cause a breach in the firewall. As long as the

tracked interface parts are used, it is still possible to query firewalld and see the

changes made by an application using this mode. The untracked passthrough mode is only

intended for services that completely take care of the own rule set, such as libvirt and

docker. The direct interface is used by adding the --direct option to the firewall-cmd

command.

The direct interface mode is intended for services or applications to add specific firewall

rules during runtime. The rules can be made permanent by adding the --permanent

option using the firewall-cmd --permanent --direct command or by modifying

/etc/firewalld/direct.xml. If the rules are not made permanent, then they need to be

applied every time after receiving the start, restart, or reload message from firewalld

using D-Bus. With the direct interface, it is possible to add chains, rules, and tracked and

untracked passthrough rules. You can also use direct rules in zone-specific chains.

4.5.2. Inst alling firewalld

In Red Hat Enterprise Linux 7, firewalld is installed by default. If required, to ensure that

it is, enter the following command as root:

~]# yum install firewalld

The graphical user interface configuration tool f irewall-co nf ig is installed by default in

some versions of Red Hat Enterprise Linux 7. If required, enter the following command as

root to ensure f irewall-conf ig is installed:

~]# yum install firewall-config

To install the optional firewall-applet, enter the following command as root:

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~]# yum install firewall-applet

The applet is visible in the panel of the desktop with the next login. The use of the applet

in GNOME is limited according to the GNOME rules for applets.

4.5.2.1. Stopping firewalld

To stop firewalld, enter the following command as root:

~]# systemctl stop firewalld

To prevent firewalld from starting automatically at system start, enter the following

command as root:

~]# systemctl disable firewalld

To make sure firewalld is not started by accessing the firewalld D-Bus interface and

also if other services require firewalld, enter the following command as root:

~]# systemctl mask firewalld

4.5.2.2. Starting firewalld

To start firewalld, enter the following command as root:

~]# systemctl unmask firewalld

~]# systemctl start firewalld

To ensure firewalld starts automatically at system start, enter the following command

as root:

~]# systemctl enable firewalld

4.5.2.3. Checking if f irewalld is Running

To check if firewalld is running, enter the following command:

~]$ systemctl status firewalld

● firewalld.service - firewalld - dynamic firewall daemon

Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled;

vendor preset: enabled)

Active: active (running) since Tue 2016-10-11 09:15:58 CEST; 2 days

ago

Docs: man:firewalld(1)

Main PID: 721 (firewalld)

CGroup: /system.slice/firewalld.service

└─721 /usr/bin/python -Es /usr/sbin/firewalld --nofork --

nopid

Oct 11 09:15:57 localhost.localdomain systemd[1]: Starting firewalld -

⁠Chapte r 4. Hardening Your System wit h T ools and Services

dynami...

Oct 11 09:15:58 localhost.localdomain systemd[1]: Started firewalld -

dynamic...

Hint: Some lines were ellipsized, use -l to show in full.

In addition, check if f irewall-cmd can connect to the daemon by entering the following

command:

~]$ firewall-cmd --state

running

4.5.3. Configuring firewalld

The firewall service, implemented by the firewalld daemon, can be configured using the

f irewall-co nf ig graphical user interface tool, using the f irewall-cmd and f irewall-

of f line-cmd command-line interface tools, and by editing XML configuration files. These

methods will be described in order.

4.5.3.1. Conf iguring firewalld Using T he Graphical User Interf ace

4.5.3.1.1. St art ing t he Graphical Firewall Conf igurat ion To o l

To start the graphical f irewall-co nf ig tool, press the Super key to enter the Activities

Overview, type firewall, and press Enter. The f irewall-conf ig tool appears. You will

be prompted for an administrator password.

To start the graphical firewall configuration tool using the command-line, enter the

following command:

~]$ firewall-config

The Firewall Configuration window opens. Note that this command can be run as a

normal user, but you will be prompted occasionally for an administrator password.

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Figure 4.2. T he Firewall Co nf igurat io n T ool

Look for the “Connection to firewalld established” message in the lower-left corner. This

indicates that the f irewall-conf ig tool is connected to firewalld. Note that the ICMP

Types, IPSets, Direct Configuration, and Lockdown Whitelist tabs are only visible

after being selected from the View drop-down menu. The Active Bindings sidebar on

the left is visible by default.

4.5.3.1.2. Changing t he Firewall Set t ings

To immediately change the current firewall settings, ensure the current view is set to

Runt ime. Alternatively, to edit the settings to be applied at the next system start or

firewall reload, select Permanent from the drop-down list.

⁠Chapte r 4. Hardening Your System wit h T ools and Services

Note

When making changes to the firewall settings in Runt ime mode, your selection

takes immediate effect when you set or clear the check box associated with the

service. You should keep this in mind when working on a system that may be in use

by other users.

When making changes to the firewall settings in Permanent mode, your selection

will only take effect when you reload the firewall or the system restarts. Click the

Opt io ns menu and select Reload Firewall.

You can select zones in the left-hand side column. You will notice the zones have some

services enabled; you may need to resize the window or scroll to see the full list. You can

customize the settings by selecting and deselecting a service.

4.5.3.1.3. Adding an Int erf ace t o a Zone

To add a connection (the interfaces used by a connection) to a zone, start f irewall-

conf ig. Click on the zone in the zone list on the left and select the Interfaces tab on the

right. Click on the Add button to rise a new dialog to add the interface.

To change the zone setting for an interface, double-click the proper connection or

interface in the Active Bindings sidebar. Select the new firewall zone from the drop-

down menu in the following dialog and confirm by clicking OK.

Alternatively, to add or reassign an interface of a connection to a zone, start f irewall-

conf ig, select Opt io ns from the menu bar, and select Change Zones of Connections

from the drop-down menu. The Connections, Interface, and Source list displays. Select

the connection to be reassigned. The Select Zone for Connection window appears.

Select the new firewall zone from the drop-down menu and click OK.

For connections handled by Net workManager, the request to change the zone is

forwarded to Net workManager. The zone interface setting will not be saved in

firewalld.

You can also use the f irewall-cmd command-line tool or the f irewall-applet applet to

change the zone for a connection, interface, and source.

The connections without specific zone settings are automatically bound to the default

zone. A change of the default zone consequently applies to the zone bindings of all such

connections.

4.5.3.1.4. Set t ing t he Def ault Zone

To set the default zone that new interfaces will be assigned to, start f irewall-co nf ig,

select Opt ions from the menu bar, and select Change Default Zone from the drop-down

menu. The Default Zone window appears. Select the zone from the list that you want to

be used as the default zone and click OK. Alternatively, enter the following command:

~]$ firewall-cmd --set-default-zone=zone-name

4.5.3.1.5. Co nf iguring Services

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To enable or disable a predefined or custom service, start the f irewall-conf ig tool and

select the network zone whose services are to be configured. Select the Services tab

and select the check box for each type of service you want to trust. Clear the check box to

block a service.

To edit a service, start the f irewall-conf ig tool and select Permanent mode from the

drop-down selection menu labeled Configuration. Additional icons and menu buttons

appear at the bottom of the Services window. Select the service you want to configure.

The Ports, Protocols, and Source Port tabs enables adding, changing, and removing of

ports, protocols, and source port for the selected service. The modules tab is for

configuring Net f ilt er helper modules. The Destination tab enables limiting traffic to a

particular destination address and Internet Protocol (IPv4 or IPv6).

Note

It is not possible to alter service settings in Runt ime mode.

4.5.3.1.6. Opening Port s in t he Firewall

To permit traffic through the firewall to a certain port, start the f irewall-conf ig tool and

select the network zone whose settings you want to change. Select the Ports tab and

click the Add button on the right-hand side. The Port and Protocol window opens.

Enter the port number or range of ports to permit. Select tcp or udp from the drop-down

list.

4.5.3.1.7. Opening Prot ocols in t he Firewall

To permit traffic through the firewall using a certain protocol, start the f irewall-conf ig

tool and select the network zone whose settings you want to change. Select the

Protocols tab and click the Add button on the right-hand side. The Protocol window

opens.

Either select a protocol from the drop-down list or select the Other Protocol check box

and enter the protocol in the field.

4.5.3.1.8. Opening Source Port s in t he Firewall

To permit traffic through the firewall from a certain port, start the firewall-config tool and

select the network zone whose settings you want to change. Select the Source Port tab

and click the Add button on the right-hand side. The Source Port window opens.

Enter the port number or range of ports to permit. Select tcp or udp from the drop-down

list.

4.5.3.1.9. Enabling IPv4 Address Masquerading

To translate IPv4 addresses to a single external address, start the f irewall-conf ig tool

and select the network zone whose addresses are to be translated. Select the

Masquerading tab and select the check box to enable the translation of IPv4 addresses

to a single address.

⁠Chapte r 4. Hardening Your System wit h T ools and Services

Note

To enable masquerading for IPv6, use a rich rule.

4.5.3.1.10. Co nf iguring Port Forwarding

To forward inbound network traffic, or “packets”, for a specific port to an internal address

or alternative port, first enable IP address masquerading, then select the Port

Forwarding tab.

Select the protocol of the incoming traffic and the port or range of ports on the upper

section of the window. The lower section is for setting details about the destination.

To forward traffic to a local port (a port on the same system), select the Local

forwarding check box. Enter the local port or range of ports for the traffic to be sent to.

To forward traffic to another IPv4 address, select the Forward to another port check

box. Enter the destination IP address and port or port range. The default is to send to the

same port if the port field is left empty. Click OK to apply the changes.

4.5.3.1.11. Conf iguring t he ICMP Filt er

To enable or disable an ICMP filter, start the f irewall-conf ig tool and select the network

zone whose messages are to be filtered. Select the ICMP Filter tab and select the

check box for each type of ICMP message you want to filter. Clear the check box to

disable a filter. This setting is per direction and the default allows everything.

To edit an ICMP type, start the f irewall-conf ig tool and select Permanent mode from

the drop-down selection menu labeled Configuration. Additional icons appear at the

bottom of the Services window. Select Yes in the following dialog to enable masquerading

and to make forwarding to another machine working.

To enable inverting the ICMP Filter, click the Invert Filter check box on the right.

Only marked ICMP types are now accepted, all other are rejected. In a zone using the

DROP target, they are dropped.

4.5.3.1.12. Conf iguring Rich Rules

To enable or disable a rich rule, start the f irewall-conf ig tool and select the network

zone whose services are to be configured. Select the Rich Rules tab and click the Add

button on the right-hand side. The Rich Rule window appears.

Select the Family the rule should be added to, leave it at ipv4 and ipv6 to add a rule for

IPv4 and IPv6. Enable the Element check box if you want to select a service, port,

protocol, icmp-block, forward-port, source port or if you want to enable masquerade

in the rule. For all elements except masquerade, it is needed to click on the button on the

right. The Service window appears to select the setting of the element.

With the Action check box, you can enable a custom action for the rule like accept,

reject, drop, or mark. If the rule Family is set to either ipv4 or ipv6, you can enable the

with the Type check box to select an alternative reject type from the drop-down menu that

matches the rule Family. Additionally, you can set a limit for this action by enabling the

With limit check box.

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In the Source section, you can select a source match for this rule. This can be an IP

address or range, a MAC address or an IP set. With the inverted check box, you can

negate this match. The IP address is only selectable if the Family is either ipv4 or ipv6.

With the Destination address, you can select an IP address matching the selected

Family. It is selectable only if the Family is either ipv4 or ipv6.

To enable logging to the system log with the rule, use the Log check box. It is necessary

to select a logging prefix in the Prefix text field. Please select the log Level. It can be

emergency, alert, critical, error, warning, notice, info or debug. With the optional

limit, the amount of log messages in the system log can be selected. If logging is enabled

the rule will be duplicated to be able to log.

To enable logging using the Linux Audit system, use the Audit check box. See the

System Auditing chapter for more information.

If the rule is complete and the OK button is active, you can add the rule. If the button is not

active, there is a tooltip that shows what is missing or not appropriate.

4.5.3.1.13. Conf iguring Sources

To add a source to a zone, start f irewall-conf ig. Click on a zone in the zone list on the

left and select the Sources tab on the right. With clicking the Add button, there will be a

new dialog to add the source. A source can either be an IP address or range, a MAC

address or an ipset. Select the type in the drop-down menu on the left and click the

button on the right to select or enter the setting.

4.5.3.1.14. Conf iguring IP Set s

To configure IP sets, start the f irewall-conf ig tool and select the IPSets tab. Select an

IP set from the list on the left to change the runtime settings of an IP set that has been

created with firewalld already.

To add new IP sets or to change base IP set settings, switch to Permanent mode.

Additional icons and menu buttons appear at the bottom of the IPSets window. Select the

IP set you want to configure. The entries tab on the right shows the entries that are part

of the IP set. There are no entries listed for IP sets that use a timeout, as the entries are

kept and handled in kernel space.

With the Add button, you can add single entries, but also entries from a file. With Remove

you can remove the selected entry, all entries and also entries from a file. The file should

contain an entry per line. Lines starting with a hash or semicolon are ignored. Also empty

lines.

After clicking on the + button to add a new IP set, a new window appears to configure the

base IP set settings. There are three settings that need to be configured for an IP set:

Name, Type, and Family. Name can contain all alphanumeric characters and additionally ‘-’,

‘-’, ‘:’, and ‘.’. The maximum name length is 32 characters. Type can be: hash:ip,

hash:net, and hash:mac. Bitmap types are not supported by firewalld as they can be

only used with IPv4. Combined types are not supported, too.

To have a simple and fast IP address or network set, use the hash:net type. The

hash:ip type expands all ranges and network segments internally and reaches the hash

limit soon.

For these types, it is also necessary to define Family. This can be either inet for IPv4 or

inet6 for IPv6.

To store MAC addresses in an IP set use hash:mac - Family is not selectable in this case.

⁠Chapte r 4. Hardening Your System wit h T ools and Services

To define a lifetime of the added entries for use with external services like fail2ban, use

the Timeout setting. Note that firewalld is not able to show the temporarily stored

entries with a timeout. Use the ipset command for such entries.

To define the initial hash size for an IP set, use the Hashsize setting. Limit the maximum

number of elements that can be stored in an IP set by using the Maxelem field.

You can use the created IP set as a source in a zone, in a rich rule, and also in a direct

rule. For more information on IP sets and the settings, see Section 4.5.4, “Using the

iptables Service”.

4.5.3.2. Conf iguring the Firewall Using the f irewall-cmd Command-Line

T ool

The f irewall-cmd command-line tool is part of the firewalld application that is installed

by default. You can verify that it is installed by checking the version or displaying the help

output. Enter the following command to check the version:

~]$ firewall-cmd --version

Enter the following command to view the help output:

~]$ firewall-cmd --help

We list a selection of commands below; for a full list see the firewall-cmd(1) man page.

Note

To make a command permanent or persistent, add the --permanent option to all

commands apart from the --direct commands (which are by their nature

temporary). Note that this not only means the change will be permanent, but that the

change will only take effect after firewalld reload, service restart, or after system

reboot. Settings made with f irewall-cmd without the --permanent option take

effect immediately but are only valid till next firewall reload, system boot, or

firewalld service restart. Reloading the firewalld does not in itself break

connections, but be aware you are discarding temporary changes by doing so.

To make a command both persistent and take effect immediately, enter the

command twice: once with the --permanent and once without. This is because a

firewalld reload takes more time than just repeating a command because it has to

reload all configuration files and recreate the whole firewall configuration. While

reloading, the policy for built-in chains is set to DROP for security reasons and is

then reset to ACCEPT at the end. Service disruption is possible during the reload.

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Figure 4.3. T he f irewalld Archit ect ure

Important

All options to change the zone binding for interfaces that are under control of

Net workManager are forwarded to Net workManager. These changes are not

applied to the firewalld configuration if the request for Net workManager

succeeds. This is also the case with the --permanent option.

For interfaces that are not under control of Net workManager, the change applies

to the firewalld configuration. If there is an ifcfg file that uses this interface, then

the ZONE= setting in this ifcfg file is adapted to make sure that the configuration in

firewalld and the ifcfg file is consistent. If there is more than one ifcfg file

using this interface then the first one is used.

See the Red Hat Enterprise Linux 7 Networking Guide for information on

Net workManager and working with ifcfg files.

For configuration settings such as the default zone, there is no difference between

the runtime and permanent environment when using the command-line and GUI

tools.

4.5.3.3. Viewing the Firewall Settings Using the Command-Line Interf ace

(CLI)

To get a text display of the state of firewalld, enter the following command:

~]$ firewall-cmd --state

To view the list of active zones with a list of the interfaces currently assigned to them,

enter the following command:

~]$ firewall-cmd --get-active-zones

public

interfaces: em1

⁠Chapte r 4. Hardening Your System wit h T ools and Services

To find out the zone that an interface, for example, em1, is currently assigned to, enter

the following command:

~]$ firewall-cmd --get-zone-of-interface=em1

public

To find out all the interfaces assigned to a zone, for example, the public zone, enter the

following command as root:

~]# firewall-cmd --zone=public --list-interfaces

em1 wlan0

This information is obtained from Net wo rkManager and only shows interfaces, not

connections.

To find out all the settings of a zone, for example, the public zone, enter the following

command as root:

~]# firewall-cmd --zone=public --list-all

public

interfaces:

services: mdns dhcpv6-client ssh

ports:

forward-ports:

icmp-blocks: source-quench

To view the zone information, use the --info-zone option. To get the verbose output with

the description and short description, use the additional -v option.

~]# firewall-cmd --info-zone=public

public (active)

target: default

icmp-block-inversion: no

interfaces: em1

sources:

services: dhcpv6-client mdns ssh

ports:

protocols:

masquerade: no

forward-ports:

source-ports:

icmp-blocks:

rich rules:

To view the list of services currently loaded, enter the following command as root:

~]# firewall-cmd --get-services

cluster-suite pop3s bacula-client smtp ipp radius bacula ftp mdns samba

dhcpv6-client dns openvpn imaps samba-client http https ntp vnc-server

telnet libvirt ssh ipsec ipp-client amanda-client tftp-client nfs tftp

libvirt-tls

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This lists the names of the predefined services loaded from

/usr/lib/firewalld/services/ as well as any custom services that are currently

loaded. Note that the configuration files themselves are named service-name.xml.

To list the custom services that have been created but not loaded, use the following

command as root:

~]# firewall-cmd --permanent --get-services

This lists all services, including custom services configured in

/etc/firewalld/services/, even if they are not yet loaded.

To show the settings of the ftp service, use the following command as root:

~]# firewall-cmd --info-service=ftp

ftp

ports: 21/tcp

protocols:

source-ports:

modules: nf_conntrack_ftp

destination:

To view the settings in permanent configuration mode, use the --permanent option.

4.5.3.4. Changing the Firewall Settings Using the Command-Line Interf ace

(CLI)

4.5.3.4.1. Dro pping All Packet s (Panic Mode)

To start dropping all incoming and outgoing packets, enter the following command as root:

~]# firewall-cmd --panic-on

All incoming and outgoing packets will be dropped. Active connections will be terminated

after a period of inactivity; the time taken depends on the individual session timeout

values.

To start passing incoming and outgoing packets again, enter the following command as

root:

~]# firewall-cmd --panic-off

After disabling panic mode, established connections might work again if panic mode was

enabled for a short period of time.

To find out if panic mode is enabled or disabled, enter the following command:

~]$ firewall-cmd --query-panic

The command prints yes with exit status 0 if enabled. It prints no with exit status 1

otherwise.

4.5.3.4.2. Relo ading t he Firewall Using the Command-Line Int erf ace (CLI)

⁠Chapte r 4. Hardening Your System wit h T ools and Services

To reload the firewall without interrupting user connections (without losing state

information), enter the following command:

~]$ firewall-cmd --reload

A firewall reload involves reloading all configuration files and recreating the whole firewall

configuration. While reloading, the policy for built-in chains is set to DROP for security

reasons and is then reset to ACCEPT at the end. Service disruption is therefore possible

during the reload. Alternatively as the root user, send the SIGHUP signal to reload the

firewall.

To reload the firewall and interrupt user connections, discarding state information, enter

the following command as root:

~]# firewall-cmd --complete-reload

This command should normally only be used in case of severe firewall problems. For

example, use this command if there are state information problems and no connection can

be established but the firewall rules are correct.

4.5.3.4.3. Add an Int erf ace t o a Zone Using t he Co mmand-Line Int erf ace (CLI)

To add an interface to a zone (for example, to add em1 to the public zone), enter the

following command as root:

~]# firewall-cmd --zone=public --add-interface=em1

To make this setting persistent, repeat the commands adding the --permanent option.

4.5.3.4.4. Add an Int erf ace t o a Zone by Edit ing t he Int erf ace Co nf igurat io n

File

To add an interface to a zone by editing the ifcfg-em1 configuration file (for example, to

add em1 to the work zone), add the following line to ifcfg-em1 as root:

ZONE=work

Note that if you omit the ZONE option, or use ZONE=, or ZONE='', then the default zone will

be used.

Net workManager will automatically reconnect and the zone will be set accordingly.

4.5.3.4.5. Co nf iguring t he Def ault Zone by Edit ing t he f irewalld Co nf igurat io n

File

As root, open /etc/firewalld/firewalld.conf and edit the file as follows:

# default zone

# The default zone used if an empty zone string is used.

# Default: public

DefaultZone=home

Reload the firewall by entering the following command as root:

~]# firewall-cmd --reload

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This will reload the firewall without losing state information (that is, TCP sessions will not

be terminated), but service disruption is possible during the reload.

4.5.3.4.6. Set t ing t he Def ault Zone by Using t he Command-Line Int erf ace (CLI)

To set the default zone (for example, to public), enter the following command as root:

~]# firewall-cmd --set-default-zone=public

This change will take effect immediately; in this case, it is not necessary to reload the

firewall.

4.5.3.4.7. Opening Port s in t he Firewall Using t he Command-Line Int erf ace (CLI)

To list all open ports for a zone (for example, dmz), enter the following command as root:

~]# firewall-cmd --zone=dmz --list-ports

Note that this will not show ports opened as a result of the --add-services command.

To add a port to a zone (for example, to allow TCP traffic to port 8080 to the dmz zone),

enter the following command as root:

~]# firewall-cmd --zone=dmz --add-port=8080/tcp

To make this setting persistent, repeat the command adding the --permanent option.

To add a range of ports to a zone (for example, to allow the ports from 5060 to 5061 to the

public zone, enter the following command as root:

~]# firewall-cmd --zone=public --add-port=5060-5061/udp

To make this setting persistent, repeat the command adding the --permanent option.

4.5.3.4.8. Opening Prot ocols Using t he Command Line Int erf ace (CLI)

To list all open ports for a zone (dmz, for example), enter the following command as root:

~]# firewall-cmd --zone=dmz --list-protocols

Note that this command does not show protocols opened as a result of the firewall-cmd

--add-services command.

To add a protocol to a zone (for example, to allow ESP traffic to the dmz zone), enter the

following command as root:

~]# firewall-cmd --zone=dmz --add-protocol=esp

To make this setting persistent, add the --permanent option.

4.5.3.4.9. Opening Source Port s Using t he Command Line Int erf ace (CLI)

⁠Chapte r 4. Hardening Your System wit h T ools and Services

To list all open source ports for a zone (for example, the dmz zone), enter the following

command as root:

~]# firewall-cmd --zone=dmz --list-source-ports

Note that this command does not show source ports opened as a result of the firewall-

cmd --add-services command.

To add a source port to a zone (for example, to allow TCP traffic from port 8080 to the

dmz zone), use the following command as root:

~]# firewall-cmd --zone=dmz --add-source-port=8080/tcp

To add a range of source ports to a zone (for example, to allow the ports from 5060 to

5061 to the public zone), enter the following command as root:

~]# firewall-cmd --zone=public --add-source-port=5060-5061/udp

To make the settings persistent, add the --permanent option.

4.5.3.4.10. Adding a Service t o a Zone Using t he Co mmand-Line Int erf ace (CLI)

To add a service to a zone (for example, to allow SMTP to the work zone), enter the

following command as root:

~]# firewall-cmd --zone=work --add-service=smtp

To make this setting persistent, repeat the command adding the --permanent option.

4.5.3.4.11. Removing a Service f rom a Zone Using t he Co mmand-Line Int erf ace

(CLI)

To remove a service from a zone (for example, to remove SMTP from the work zone),

enter the following command as root:

~]# firewall-cmd --zone=work --remove-service=smtp

To make this change persistent, repeat the command adding the --permanent option. This

change will not break established connections. If that is your intention, you can use the --

complete-reload option, but this will break all established connections — not just for the

service you have removed.

4.5.3.4.12. Adding a Service t o a Zo ne by Edit ing XML Files

To view the default zone files, enter the following command as root:

~]# ls /usr/lib/firewalld/zones/

block.xml drop.xml home.xml public.xml work.xml

dmz.xml external.xml internal.xml trusted.xml

These files must not be edited. They are used by default if no equivalent file exists in the

/etc/firewalld/zones/ directory.

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To view the zone files that have been changed from the default, enter the following

command as root:

~]# ls /etc/firewalld/zones/

external.xml public.xml public.xml.old

In the example shown above, the work zone file does not exist. To add the work zone file,

enter the following command as root:

~]# cp /usr/lib/firewalld/zones/work.xml /etc/firewalld/zones/

You can now edit the file in the /etc/firewalld/zones/ directory. If you delete the file,

firewalld will fall back to using the default file in /usr/lib/firewalld/zones/.

To add a service to a zone (for example, to allow SMTP to the work zone), add the following

line to the /etc/firewalld/zones/work.xml file as root:

4.5.3.4.13. Removing a Service f rom a Zone by Edit ing XML f iles

An editor running with root privileges is required to edit the XML zone files. To view the

files for previously configured zones, enter the following command as root:

~]# ls /etc/firewalld/zones/

external.xml public.xml work.xml

To remove a service from a zone (for example, to remove SMTP from the work zone), use

an editor with root privileges to edit the /etc/firewalld/zones/work.xml file to remove

the following line:

If no other changes have been made to the work.xml file, it can be removed and

firewalld will use the default /usr/lib/firewalld/zones/work.xml configuration file

after the next reload or system boot.

4.5.3.4.14. Conf iguring IP Address Masquerading

To check if IP masquerading is enabled (for example, for the external zone), enter the

following command as root:

~]# firewall-cmd --zone=external --query-masquerade

The command prints yes with exit status 0 if enabled. It prints no with exit status 1

otherwise. If zone is omitted, the default zone will be used.

To enable IP masquerading, enter the following command as root:

~]# firewall-cmd --zone=external --add-masquerade

To make this setting persistent, repeat the command adding the --permanent option.

To disable IP masquerading, enter the following command as root:

⁠Chapte r 4. Hardening Your System wit h T ools and Services

~]# firewall-cmd --zone=external --remove-masquerade

To make this setting persistent, repeat the command adding the --permanent option.

4.5.3.4.15. Conf iguring Po rt Forwarding Using t he Command-Line Int erf ace

(CLI)

To forward inbound network packets from one port to an alternative port or address, first

enable IP address masquerading for a zone (for example, external), by entering the

following command as root:

~]# firewall-cmd --zone=external --add-masquerade

To forward packets to a local port (a port on the same system), enter the following

command as root:

~]# firewall-cmd --zone=external --add-forward-

port=port=22:proto=tcp:toport=3753

In this example, the packets intended for port 22 are now forwarded to port 3753. The

original destination port is specified with the port option. This option can be a port or port

range, together with a protocol. The protocol, if specified, must be one of either tcp or

udp. The new local port (the port or range of ports to which the traffic is being forwarded

to) is specified with the toport option. To make this setting persistent, repeat the

commands adding the --permanent option.

To forward packets to another IPv4 address, usually an internal address, without changing

the destination port, enter the following command as root:

~]# firewall-cmd --zone=external --add-forward-

port=port=22:proto=tcp:toaddr=192.0.2.55

In this example, the packets intended for port 22 are now forwarded to the same port at

the address given with the toaddr. The original destination port is specified with the port

option. This option can be a port or port range, together with a protocol. The protocol, if

specified, must be one of either tcp or udp. The new destination port (the port or range of

ports to which the traffic is being forwarded to) is specified with the toport option. To

make this setting persistent, repeat the command adding the --permanent option.

To forward packets to another port at another IPv4 address, usually an internal address,

enter the following command as root:

~]# firewall-cmd --zone=external \

--add-forward-port=port=22:proto=tcp:toport=2055:toaddr=192.0.2.55

In this example, the packets intended for port 22 are now forwarded to port 2055 at the

address given with the toaddr option. The original destination port is specified with the

port option. This option can be a port or port range, together with a protocol. The protocol,

if specified, must be one of either tcp or udp. The new destination port, the port or range

of ports to which the traffic is being forwarded to, is specified with the toport option. To

make this setting persistent, repeat the command adding the --permanent option.

4.5.3.5. Conf iguring the Firewall Using XML Files

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The configuration settings for f irewalld are stored in XML files in the /etc/firewalld/

directory. Do not edit the files in the /usr/lib/firewalld/ directory (the files define the

default settings). You will need root user permissions to view and edit the XML files. The

XML files are explained in three man pages:

firewalld.icmptype(5) man page — Describes XML configuration files for ICMP

filtering.

firewalld.service(5) man page — Describes XML configuration files for f irewalld

service.

firewalld.zone(5) man page — Describes XML configuration files for firewalld zone

configuration.

The XML files can be created and edited directly or created indirectly using the graphical

and command-line tools. Organizations can distribute them in RPM files, which can make

management and version control easier. Tools like Puppet can distribute such

configuration files.

4.5.3.6. Using the Direct Interf ace

It is possible to add and remove chains during runtime by using the --direct option with

the f irewall-cmd tool. A few examples are presented here. See the firewall-cmd(1)

man page for more information.

It is dangerous to use the direct interface if you are not very familiar with ipt ables as

you could inadvertently cause a breach in the firewall.

The direct interface mode is intended for services or applications to add specific firewall

rules during runtime. The rules can be made permanent by adding the --permanent

option using the firewall-cmd --permanent --direct command or by modifying

/etc/firewalld/direct.xml. See man firewalld.direct(5) for information on the

/etc/firewalld/direct.xml file.

4.5.3.6.1. Adding a Rule Using t he Direct Int erf ace

To add a rule to the “IN_public_allow” chain, enter the following command as root:

~]# firewall-cmd --direct --add-rule ipv4 filter IN_public_allow \

0 -m tcp -p tcp --dport 666 -j ACCEPT

Add the --permanent option to make the setting persistent.

4.5.3.6.2. Removing a Rule Using t he Direct Int erf ace

To remove a rule from the “IN_public_allow” chain, enter the following command as root:

~]# firewall-cmd --direct --remove-rule ipv4 filter IN_public_allow \

0 -m tcp -p tcp --dport 666 -j ACCEPT

Add the --permanent option to make the setting persistent.

4.5.3.6.3. List ing Rules Using t he Direct Int erf ace

To list the rules in the “IN_public_allow” chain, enter the following command as root:

⁠Chapte r 4. Hardening Your System wit h T ools and Services

~]# firewall-cmd --direct --get-rules ipv4 filter IN_public_allow

Note that this command (the --get-rules option) only lists rules previously added using

the --add-rule option. It does not list existing ipt ables rules added by other means.

4.5.3.7. Conf iguring Complex Firewall Rules with the "Rich Language"

Syntax

With the “rich language” syntax, complex firewall rules can be created in a way that is

easier to understand than the direct-interface method. In addition, the settings can be

made permanent. The language uses keywords with values and is an abstract

representation of ipt ables rules. Zones can be configured using this language; the

current configuration method will still be supported.

4.5.3.7.1. Fo rmat t ing of t he Rich Language Co mmands

All the commands in this section need to be run as root. The format of the command to

add a rule is as follows:

firewall-cmd [--zone=zone] --add-rich-rule='rule' [--timeout=timeval]

This will add a rich language rule rule for zone zone. This option can be specified multiple

times. If the zone is omitted, the default zone is used. If a timeout is supplied, the rule or

rules only stay active for the amount of time specified and will be removed automatically

afterwards. The time value can be followed by s (seconds), m (minutes), or h (hours) to

specify the unit of time. The default is seconds.

To remove a rule:

firewall-cmd [--zone=zone] --remove-rich-rule='rule'

This will remove a rich language rule rule for zone zone. This option can be specified

multiple times. If the zone is omitted, the default zone is used.

To check if a rule is present:

firewall-cmd [--zone=zone] --query-rich-rule='rule'

This will return whether a rich language rule rule has been added for the zone zone. The

command prints yes with exit status 0 if enabled. It prints no with exit status 1 otherwise.

If the zone is omitted, the default zone is used.

For information about the rich language representation used in the zone configuration

files, see the firewalld.zone(5) man page.

4.5.3.7.2. Underst anding t he Rich Rule St ruct ure

The format or structure of the rich rule commands is as follows:

rule [family="rule family"]

[ source [NOT] [address="address"] [mac="mac-address"]

[ipset="ipset"] ]

[ destination [NOT] address="address" ]

[ element ]

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[ log [prefix="prefix text"] [level="log level"] [limit

value="rate/duration"] ]

[ audit ]

[ action ]

Note

The structure of the rich rule in the file uses the NOT keyword to invert the sense of

the source and destination address commands, but the command line uses the

invert="true" option.

A rule is associated with a particular zone. A zone can have several rules. If some rules

interact or contradict, the first rule that matches the packet applies.

4.5.3.7.3. Underst anding t he Rich Rule Command Opt ions

family

If the rule family is provided, either ipv4 or ipv6, it limits the rule to IPv4 or

IPv6, respectively. If the rule family is not provided, the rule is added for both

IPv4 and IPv6. If source or destination addresses are used in a rule, then the

rule family needs to be provided. This is also the case for port forwarding.

So urce and Dest inat ion Addresses

source

By specifying the source address, the origin of a connection attempt can be

limited to the source address. A source address or address range is either an IP

address or a network IP address with a mask for IPv4 or IPv6. For IPv4, the

mask can be a network mask or a plain number. For IPv6, the mask is a plain

number. The use of host names is not supported. It is possible to invert the

sense of the source address command by adding the NOT keyword; all but the

supplied address matches.

A MAC address and also an IP set with type hash:mac can be added for IPv4 and

IPv6 if no family is specified for the rule. Other IP sets need to match the

family setting of the rule.

destination

By specifying the destination address, the target can be limited to the destination

address. The destination address uses the same syntax as the source address

for IP address or address ranges. The use of source and destination addresses

is optional, and the use of a destination addresses is not possible with all

elements. This depends on the use of destination addresses, for example, in

service entries. You can combine destination and action.

Element s

The element can be o nly one of the following element types: service, port, protocol,

masquerade, icmp-block, forward-port, and source-port.

service

The service element is one of the f irewalld provided services. To get a list of

⁠Chapte r 4. Hardening Your System wit h T ools and Services

The service element is one of the f irewalld provided services. To get a list of

the predefined services, enter the following command:

~]$ firewall-cmd --get-services

If a service provides a destination address, it will conflict with a destination

address in the rule and will result in an error. The services using destination

addresses internally are mostly services using multicast. The command takes

the following form:

service name=service_name

port

The port element can either be a single port number or a port range, for

example, 5060-5062, followed by the protocol, either as tcp or udp. The

command takes the following form:

port port=number_or_range protocol=protocol

protocol

The protocol value can be either a protocol ID number or a protocol name. For

allowed protocol entries, see /etc/protocols. The command takes the

following form:

protocol value=protocol_name_or_ID

icmp-block

Use this command to block one or more ICMP types. The ICMP type is one of the

ICMP types f irewalld supports. To get a listing of supported ICMP types, enter

the following command:

~]$ firewall-cmd --get-icmptypes

Specifying an action is not allowed here. icmp-block uses the action reject

internally. The command takes the following form:

icmp-block name=icmptype_name

masquerade

Turns on IP masquerading in the rule. A source address can be provided to limit

masquerading to this area, but not a destination address. Specifying an action is

not allowed here.

forward-port

Forward packets from a local port with protocol specified as tcp or udp to either

another port locally, to another machine, or to another port on another machine.

The port and to-port can either be a single port number or a port range. The

destination address is a simple IP address. Specifying an action is not allowed

here. The forward-port command uses the action accept internally. The

command takes the following form:

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forward-port port=number_or_range protocol=protocol /

to-port=number_or_range to-addr=address

source-port

Matches the source port of the packet - the port that is used on the origin of a

connection attempt. To match a port on current machine, use the port element.

The source-port element can either be a single port number or a port range (for

example, 5060-5062) followed by the protocol as tcp or udp. The command takes

the following form:

source-port port=number_or_range protocol=protocol

Logging

log

Log new connection attempts to the rule with kernel logging, for example, in

syslog. You can define a prefix text that will be added to the log message as a

prefix. Log level can be one of emerg, alert, crit, error, warning, notice, info,

or debug. The use of log is optional. It is possible to limit logging as follows:

log [prefix=prefix text] [level=log level] limit

value=rate/duration

The rate is a natural positive number [1, ..], with the duration of s, m, h, d. s means

seconds, m means minutes, h means hours, and d days. The maximum limit value

is 1/d, which means at maximum one log entry per day.

audit

Audit provides an alternative way for logging using audit records sent to the

service auditd. The audit type can be one of ACCEPT, REJECT, or DROP, but it is

not specified after the command audit as the audit type will be automatically

gathered from the rule action. Audit does not have its own parameters, but limit

can be added optionally. The use of audit is optional.

Act ion

accept|reject|drop|mark

An action can be one of accept, reject, drop, or mark. The rule can only contain

an element or a source. If the rule contains an element, then new connections

matching the element will be handled with the action. If the rule contains a source,

then everything from the source address will be handled with the action

specified.

accept | reject [type=reject type] | drop | mark

set="mark[/mask]"

With accept, all new connection attempts will be granted. With reject, they will

be rejected and their source will get a reject message. The reject type can be

set to use another value. With drop, all packets will be dropped immediately and

no information is sent to the source. With mark all packets will be marked with the

given mark and the optional mask.

⁠Chapte r 4. Hardening Your System wit h T ools and Services

4.5.3.7.4. Using t he Rich Rule Log Co mmand

Logging can be done with the Net f ilt er log target and also with the audit target. A new

chain is added to all zones with a name in the format “zone_log”, where zone is the zone

name. This is processed before the deny chain to have the proper ordering. The rules or

parts of them are placed in separate chains, according to the action of the rule, as follows:

zone_log

zone_deny

zone_allow

All logging rules will be placed in the “zone_log” chain, which will be parsed first. All reject

and drop rules will be placed in the “zone_deny” chain, which will be parsed after the log

chain. All accept rules will be placed in the “zone_allow” chain, which will be parsed after

the deny chain. If a rule contains log and also deny or allow actions, the parts of the rule

that specify these actions are placed in the matching chains.

4.5.3.7.4.1. Using t he Rich Rule Log Command Example 1

Enable new IPv4 and IPv6 connections for authentication header protocol AH:

rule protocol value="ah" accept

4.5.3.7.4.2. Using t he Rich Rule Log Command Example 2

Allow new IPv4 and IPv6 connections for protocol FTP and log 1 per minute using audit:

rule service name="ftp" log limit value="1/m" audit accept

4.5.3.7.4.3. Using t he Rich Rule Log Command Example 3

Allow new IPv4 connections from address 192.168.0.0/24 for protocol TFTP and log 1 per

minute using syslog:

rule family="ipv4" source address="192.168.0.0/24" service name="tftp"

log prefix="tftp" level="info" limit value="1/m" accept

4.5.3.7.4.4. Using t he Rich Rule Log Command Example 4

New IPv6 connections from 1:2:3:4:6:: for protocol RADIUS are all rejected and logged

at a rate of 3 per minute. New IPv6 connections from other sources are accepted:

rule family="ipv6" source address="1:2:3:4:6::" service name="radius"

log prefix="dns" level="info" limit value="3/m" reject

rule family="ipv6" service name="radius" accept

4.5.3.7.4.5. Using t he Rich Rule Log Command Example 5

Forward IPv6 packets received from 1:2:3:4:6:: on port 4011 with protocol TCP to

1::2:3:4:7 on port 4012.

rule family="ipv6" source address="1:2:3:4:6::" forward-port to-

addr="1::2:3:4:7" to-port="4012" protocol="tcp" port="4011"

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4.5.3.7.4.6. Using t he Rich Rule Log Command Example 6

Whitelist a source address to allow all connections from this source.

rule family="ipv4" source address="192.168.2.2" accept

See the firewalld.richlanguage(5) man page for more examples.

4.5.3.8. Firewall Lockdown

Local applications or services are able to change the firewall configuration if they are

running as root (for example, libvirt ). With this feature, the administrator can lock the

firewall configuration so that either no applications or only applications that are added to

the lockdown whitelist are able to request firewall changes. The lockdown settings default

to disabled. If enabled, the user can be sure that there are no unwanted configuration

changes made to the firewall by local applications or services.

4.5.3.8.1. Co nf iguring Firewall Lockdo wn

Using an editor running as root, add the following line to the

/etc/firewalld/firewalld.conf file as follows:

Lockdown=yes

Reload the firewall using the following command as root:

~]# firewall-cmd --reload

Try to enable the imaps service in the default zone using the following command as an

administrative user (a user in the wheel group; usually the first user on the system). You

will be prompted for the user password:

~]$ firewall-cmd --add-service=imaps

Error: ACCESS_DENIED: lockdown is enabled

To enable the use of f irewall-cmd, enter the following command as root:

~]# firewall-cmd --add-lockdown-whitelist-command='/usr/bin/python -Es

/usr/bin/firewall-cmd*'

Add the --permanent option if you want to make it persistent.

Reload the firewall as root:

~]# firewall-cmd --reload

Try to enable the imaps service again in the default zone by entering the following

command as an administrative user. You will be prompted for the user password:

~]$ firewall-cmd --add-service=imaps

This time the command succeeds.

⁠Chapte r 4. Hardening Your System wit h T ools and Services

4.5.3.8.2. Co nf iguring IP Set o pt ions wit h t he Command-Line Client

IP sets can be used in firewalld zones as sources and also as sources in rich rules. It is

also possible to use the IP sets created with firewalld in a direct rule.

To list the IP sets known to firewalld in the permanent environment, use the following

command as root:

~]# firewall-cmd --permanent --get-ipsets

To add a new IP set, use the following command using the permanent environment as

root:

~]# firewall-cmd --permanent --new-ipset=test --type=hash:net

success

The previous command creates a new IP set with the name test and the hash:net type

for IPv4. To create an IP set for use with IPv6, add the --option=family=inet6 option.

To make the new setting effective in the runtime environment, reload firewalld. List the

new IP set with the following command as root:

~]# firewall-cmd --permanent --get-ipsets

test

To get more information about the IP set, use the following command as root:

~]# firewall-cmd --permanent --info-ipset=test

test

type: hash:net

options:

entries:

Note that the IP set does not have any entries at the moment. To add an entry to the test

IP set, use the following command as root:

~]# firewall-cmd --permanent --ipset=test --add-entry=192.168.0.1

success

The previous command adds the IP address 192.168.0.1 to the IP set. To get the list of

current entries in the IP set, use the following command as root:

~]# firewall-cmd --permanent --ipset=test --get-entries

192.168.0.1

Generate a file containing a list of IP addresses, for example:

~]# cat > iplist.txt <<EOL

192.168.0.2

192.168.0.3

192.168.1.0/24

192.168.2.254

EOL

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The file with the list of IP addresses for an IP set should contain an entry per line. Lines

starting with a hash, a semi-colon, or empty lines are ignored.

To add the addresses from the iplist.txt file, use the following command as root:

~]# firewall-cmd --permanent --ipset=test --add-entries-from-

file=iplist.txt

success

To see the extended entries list of the IP set, use the following command as root:

~]# firewall-cmd --permanent --ipset=test --get-entries

192.168.0.1

192.168.0.2

192.168.0.3

192.168.1.0/24

192.168.2.254

To remove the addresses from the IP set and to check the updated entries list, use the

following commands as root:

~]# firewall-cmd --permanent --ipset=test --remove-entries-from-

file=iplist.txt

success

~]# firewall-cmd --permanent --ipset=test --get-entries 192.168.0.1

You can add the IP set as a source to a zone to handle all traffic coming in from any of the

addresses listed in the IP set with a zone. For example, to add the test IP set as a source

to the drop zone to drop all packets coming from all entries listed in the test IP set, use

the following command as root:

~]# firewall-cmd --permanent --zone=drop --add-source=ipset:test

success

The ipset: prefix in the source shows firewalld that the source is an IP set and not an

IP address or an address range.

Only the creation and removal of IP sets is limited to the permanent environment, all

other IP set options can be used also in the runtime environment without the --permanent

option.

4.5.3.8.3. Co nf iguring Lockdo wn wit h t he Co mmand-Line Client

To query whether lockdown is enabled, use the following command as root:

~]# firewall-cmd --query-lockdown

The command prints yes with exit status 0 if lockdown is enabled. It prints no with exit

status 1 otherwise.

To enable lockdown, enter the following command as root:

~]# firewall-cmd --lockdown-on

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To disable lockdown, use the following command as root:

~]# firewall-cmd --lockdown-off

4.5.3.8.4. Co nf iguring Lockdo wn Whit elist Opt ions wit h t he Co mmand Line

The lockdown whitelist can contain commands, security contexts, users and user IDs. If a

command entry on the whitelist ends with an asterisk “*”, then all command lines starting

with that command will match. If the “*” is not there then the absolute command including

arguments must match.

The context is the security (SELinux) context of a running application or service. To get the

context of a running application use the following command:

~]$ ps -e --context

That command returns all running applications. Pipe the output through the grep tool to get

the application of interest. For example:

~]$ ps -e --context | grep example_program

To list all command lines that are on the whitelist, enter the following command as root:

~]# firewall-cmd --list-lockdown-whitelist-commands

To add a command command to the whitelist, enter the following command as root:

~]# firewall-cmd --add-lockdown-whitelist-command='/usr/bin/python -Es

/usr/bin/command'

To remove a command command from the whitelist, enter the following command as root:

~]# firewall-cmd --remove-lockdown-whitelist-command='/usr/bin/python -

Es /usr/bin/command'

To query whether the command command is on the whitelist, enter the following command

as root:

~]# firewall-cmd --query-lockdown-whitelist-command='/usr/bin/python -Es

/usr/bin/command'

The command prints yes with exit status 0 if true. It prints no with exit status 1 otherwise.

To list all security contexts that are on the whitelist, enter the following command as root:

~]# firewall-cmd --list-lockdown-whitelist-contexts

To add a context context to the whitelist, enter the following command as root:

~]# firewall-cmd --add-lockdown-whitelist-context=context

Add the --permanent option to make it persistent.

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To remove a context context from the whitelist, enter the following command as root:

~]# firewall-cmd --remove-lockdown-whitelist-context=context

Add the --permanent option to make it persistent.

To query whether the context context is on the whitelist, enter the following command as

root:

~]# firewall-cmd --query-lockdown-whitelist-context=context

Prints yes with exit status 0, if true, prints no with exit status 1 otherwise.

To list all user IDs that are on the whitelist, enter the following command as root:

~]# firewall-cmd --list-lockdown-whitelist-uids

To add a user ID uid to the whitelist, enter the following command as root:

~]# firewall-cmd --add-lockdown-whitelist-uid=uid

Add the --permanent option to make it persistent.

To remove a user ID uid from the whitelist, enter the following command as root:

~]# firewall-cmd --remove-lockdown-whitelist-uid=uid

Add the --permanent option to make it persistent.

To query whether the user ID uid is on the whitelist, enter the following command:

~]$ firewall-cmd --query-lockdown-whitelist-uid=uid

Prints yes with exit status 0, if true, prints no with exit status 1 otherwise.

To list all user names that are on the whitelist, enter the following command as root:

~]# firewall-cmd --list-lockdown-whitelist-users

To add a user name user to the whitelist, enter the following command as root:

~]# firewall-cmd --add-lockdown-whitelist-user=user

Add the --permanent option to make it persistent.

To remove a user name user from the whitelist, enter the following command as root:

~]# firewall-cmd --remove-lockdown-whitelist-user=user

Add the --permanent option to make it persistent.

To query whether the user name user is on the whitelist, enter the following command:

~]$ firewall-cmd --query-lockdown-whitelist-user=user

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103

Prints yes with exit status 0, if true, prints no with exit status 1 otherwise.

4.5.3.8.5. Co nf iguring Lockdo wn Whit elist Opt ions wit h Conf igurat ion Files

The default whitelist configuration file contains the Net wo rkManager context and the

default context of libvirt . The user ID 0 is also in the list.

<?xml version="1.0" encoding="utf-8"?>

</whitelist>

Following is an example whitelist configuration file enabling all commands for the

firewall-cmd utility, for a user called user whose user ID is 815:

<?xml version="1.0" encoding="utf-8"?>

</whitelist>

This example shows both user id and user name, but only one option is required. Python

is the interpreter and is prepended to the command line. You can also use a specific

command, for example:

/usr/bin/python /bin/firewall-cmd --lockdown-on

In that example only the --lockdown-on command will be allowed.

Note

In Red Hat Enterprise Linux 7, all utilities are placed in the /usr/bin/ directory and

the /bin/ directory is sym-linked to the /usr/bin/ directory. In other words,

although the path for firewall-cmd when run as root might resolve to

/bin/firewall-cmd, /usr/bin/firewall-cmd can now be used. All new scripts

should use the new location. But be aware that if scripts that run as root have been

written to use the /bin/firewall-cmd path, then that command path must be

whitelisted in addition to the /usr/bin/firewall-cmd path traditionally used only for

non-root users.

The “*” at the end of the name attribute of a command means that all commands

that start with this string will match. If the “*” is not there then the absolute

command including arguments must match.

4.5.3.9. Conf iguring Logging f or Denied Packets

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With the LogDenied option in the firewalld, it is possible to add a simple logging

mechanism for denied packets. These are the packets that are rejected or dropped. To

change the setting of the logging, edit the /etc/firewalld/firewalld.conf file or use

the command-line or GUI configuration tool.

If LogDenied is enabled, logging rules are added right before the reject and drop rules in

the INPUT, FORWARD and OUTPUT chains for the default rules and also the final reject and

drop rules in zones. The possible values for this setting are: all, unicast, broadcast,

multicast, and off. The default setting is off. With the unicast, broadcast, and

multicast setting, the pkttype match is used to match the link-layer packet type. With

all, all packets are logged.

To list the actual LogDenied setting with firewall-cmd, use the following command as root:

~]# firewall-cmd --get-log-denied

off

To change the LogDenied setting, use the following command as root:

~]# firewall-cmd --set-log-denied=all

success

To change the LogDenied setting with the firewalld GUI configuration tool, start

f irewall-co nf ig, click the Options menu and select Change Log Denied menuitem. The

LogDenied window appears. Select the new LogDenied setting from the drop-down menu

and click OK.

4.5.4. Using the ipt ables Service

To use the iptables and ip6tables services instead of firewalld, first disable

firewalld by running the following command as root:

~]# systemctl disable firewalld

~]# systemctl stop firewalld

Then install the iptables-services package by entering the following command as root:

~]# yum install iptables-services

The iptables-services package contains the iptables service and the ip6tables service.

Then, to start the iptables and ip6tables services, enter the following commands as

root:

~]# systemctl start iptables

~]# systemctl start ip6tables

To enable the services to start on every system start, enter the following commands:

~]# systemctl enable iptables

~]# systemctl enable ip6tables

4.5.4.1. IPT ables and IP Sets

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105

The ipset utility is used to administer IP sets in the Linux kernel. An IP set is a framework

for storing IP addresses, port numbers, IP and MAC address pairs, or IP address and port

number pairs. The sets are indexed in such a way that very fast matching can be made

against a set even when the sets are very large. IP sets enable simpler and more

manageable configurations as well as providing performance advantages when using

ipt ables. The ipt ables matches and targets referring to sets create references which

protect the given sets in the kernel. A set cannot be destroyed while there is a single

reference pointing to it.

The use of ipset enables ipt ables commands, such as those below, to be replaced by a

set:

~]# iptables -A INPUT -s 10.0.0.0/8 -j DROP

~]# iptables -A INPUT -s 172.16.0.0/12 -j DROP

~]# iptables -A INPUT -s 192.168.0.0/16 -j DROP

The set is created as follows:

~]# ipset create my-block-set hash:net

~]# ipset add my-block-set 10.0.0.0/8

~]# ipset add my-block-set 172.16.0.0/12

~]# ipset add my-block-set 192.168.0.0/16

The set is then referenced in an ipt ables command as follows:

~]# iptables -A INPUT -m set --set my-block-set src -j DROP

If the set is used more than once a saving in configuration time is made. If the set

contains many entries a saving in processing time is made.

4.5.4.1.1. Using IP Set s wit h f irewalld

To use IP sets with f irewalld, a permanent direct rule is required to reference the set,

and a custom service must be created and started before f irewalld starts for every

ipset. You can add permanent direct rules with the /etc/firewalld/direct.xml file.

Pro cedure 4.1. Conf iguring a Cust om Service f or an IP Set

Configure a custom service to create and load the IP set structure before f irewalld

starts.

1. Using an editor running as root, create a file as follows:

~]# vi /etc/systemd/system/ipset_name.service

[Unit]

Description=ipset_name

Before=firewalld.service

[Service]

Type=oneshot

RemainAfterExit=yes

ExecStart=/usr/local/bin/ipset_name.sh start

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ExecStop=/usr/local/bin/ipset_name.sh stop

[Install]

WantedBy=basic.target

2. Use the IP set permanently in f irewalld:

~]# vi /etc/firewalld/direct.xml

<?xml version="1.0" encoding="utf-8"?>

<rule ipv="ipv4" table="filter" chain="INPUT" priority="0">-m

set

--match-set <replaceable>ipset_name</replaceable> src -j

DROP</rule>

</direct>

3. A f irewalld reload is required to activate the changes:

~]# firewall-cmd --reload

This will reload the firewall without losing state information (TCP sessions will not

be terminated), but service disruption is possible during the reload.

4.5.4.1.2. Inst alling ipset

To install the ipset utility, enter the following command as root:

~]# yum install ipset

To see the usage message:

~]$ ipset --help

ipset v6.11

Usage: ipset [options] COMMAND

output truncated

4.5.4.1.3. ipset Commands

The format of the ipset command is as follows:

ipset [options] command [command-options]

Where command is one of:

rename | swap | help | version | -

Allowed options are:

-name | -terse

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The create command is used to create a new data structure to store a set of IP data. The

add command adds new data to the set, the data added is referred to as an element of

the set.

The -exist option suppresses error message if the element already exists, and it has a

special role in updating a time out value. To change a time out, use the ipset add

command and specify all the data for the element again, changing only the time out value

as required, and using the -exist option.

The test option is for testing if the element already exists within a set.

The format of the create command is as follows:

ipset create set-name type-name [create-options]

The set-name is a suitable name chosen by the user, the type-name is the name of the

data structure used to store the data comprising the set. The format of the type-name is

as follows:

method:datatype[,datatype[,datatype]]

The allowed methods for storing data are:

bitmap | hash | list

The allowed data types are:

ip | net | mac | port | iface

When adding, deleting, or testing entries in a set, the same comma separated data syntax

must be used for the data that makes up one entry, or element, in the set. For example:

ipset add set-name ipaddr,portnum,ipaddr

Note

A set cannot contain IPv4 and IPv6 addresses at the same time. When a set is

created it is bound to a family, inet for IPv4 or inet6 for IPv6, and the default is

inet.

Example 4.2. Creat e an IP Set

To create an IP set consisting of a source IP address, a port, and destination IP address,

run a command as follows:

~]# ipset create my-set hash:ip,port,ip

Once the set is created, entries can be added as follows:

~]# ipset add my-set 192.168.1.2,80,192.168.2.2

~]# ipset add my-set 192.168.1.2,443,192.168.2.2

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The set types have the following optional parameters in common. They must be specified

when the set is created in order for them to be used:

timeout — The value given with the create command will be the default value for the

set created. If a value is given with the add command, it will be the initial non-default

value for the element.

counters — If the option is given with the create command then packet and byte

counters are created for every element in the set. If no value is given with the add

command then the counters start from zero.

comment — If the option is given with the create command then a quoted string of text

can be passed with the add command to document the purpose of the element being

added. Note that quotation marks are not allowed within the string, and escape

characters will have no effect within IP set.

Example 4.3. List an IP Set

To list the contents of a specific IP Set, my-set, run a command as follows:

~]# ipset list my-set

Name: my-set

Type: hash:ip,port,ip

Header: family inet hashsize 1024 maxelem 65536

Size in memory: 8360

References: 0

Members:

192.168.1.2,tcp:80,192.168.2.2

192.168.1.2,tcp:443,192.168.2.2

Omit the set name to list all sets.

Example 4.4. Test the Element s of an IP Set

Listing the contents of large sets is time consuming. You can test for the existence of

an element as follows:

~]# ipset test my-set 192.168.1.2,80,192.168.2.2

192.168.1.2,tcp:80,192.168.2.2 is in set my-set.

4.5.4.1.4. IP Set T ypes

bit map:ip

Stores an IPv4 host address, a network range, or an IPv4 network addresses with

the prefix-length in CIDR notation if the netmask option is used when the set is

created. It can optionally store a timeout value, a counter value, and a comment. It

can store up to 65536 entries. The command to create the bitmap:ip set has the

following format:

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ipset create set-name range start_ipaddr-end_ipaddr

|ipaddr/prefix-length [netmask prefix-length] [timeout value]

[counters] [comment]

Example 4.5. Creat e an IP Set f or a Range of Addresses Using a Pref ix Lengt h

To create an IP set for a range of addresses using a prefix length, make use of the

bitmap:ip set type as follows:

~]# ipset create my-range bitmap:ip range 192.168.33.0/28

Once the set is created, entries can be added as follows:

~]# ipset add my-range 192.168.33.1

Review the members of the list:

~]# ipset list my-range

Name: my-range

Type: bitmap:ip

Header: range 192.168.33.0-192.168.33.15

Size in memory: 84

References: 0

Members:

192.168.33.1

To add a range of addresses:

~]# ipset add my-range 192.168.33.2-192.168.33.4

Review the members of the list:

~]# ipset list my-range

Name: my-range

Type: bitmap:ip

Header: range 192.168.33.0-192.168.33.15

Size in memory: 84

References: 0

Members:

192.168.33.1

192.168.33.2

192.168.33.3

192.168.33.4

Example 4.6. Creat e an IP Set f or a Range of Addresses Using a Net mask

To create an IP set for a range of address using a netmask, make use of the bitmap:ip

set type as follows:

~]# ipset create my-big-range bitmap:ip range 192.168.124.0-

192.168.126.0 netmask 24

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Once the set is created, entries can be added as follows:

~]# ipset add my-big-range 192.168.124.0

If you attempt to add an address, the range containing that address will be added:

~]# ipset add my-big-range 192.168.125.150

~]# ipset list my-big-range

Name: my-big-range

Type: bitmap:ip

Header: range 192.168.124.0-192.168.126.255 netmask 24

Size in memory: 84

References: 0

Members:

192.168.124.0

192.168.125.0

bit map:ip,mac

Stores an IPv4 address and a MAC address as a pair. It can store up to 65536

entries.

ipset create my-range bitmap:ip,mac range start_ipaddr-end_ipaddr

| ipaddr/prefix-length [timeout value ] [counters] [comment]

Example 4.7. Creat e an IP Set f or a Range of IPv4 MAC Address Pairs

To create an IP set for a range of IPv4 MAC address pairs, make use of the

bitmap:ip,mac set type as follows:

~]# ipset create my-range bitmap:ip,mac range 192.168.1.0/24

It is not necessary to specify a MAC address when creating the set.

Once the set is created, entries can be added as follows:

~]# ipset add my-range 192.168.1.1,12:34:56:78:9A:BC

bit map:port

Stores a range of ports. It can store up to 65536 entries.

ipset create my-port-range bitmap:port range start_port-end_port

[timeout value ] [counters] [comment]

The set match and SET target netfilter kernel modules interpret the stored

numbers as TCP or UDP port numbers. The protocol can optionally be specified

together with the port. The proto only needs to be specified if a service name is

used, and that name does not exist as a TCP service.

Example 4.8. Creat e an IP Set f or a Range of Po rts

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To create an IP set for a range of ports, make use of the bitmap:port set type as

follows:

~]# ipset create my-permitted-port-range bitmap:port range 1024-49151

Once the set is created, entries can be added as follows:

~]# ipset add my-permitted-port-range 5060-5061

hash:ip

Stores a host or network address in the form of a hash. By default, an address

specified without a network prefix length is a host address. The all-zero IP

address cannot be stored.

ipset create my-addresses hash:ip [family[ inet | inet6 ]]

[hashsize value] [maxelem value ] [netmask prefix-length]

[timeout value ]

The inet family is the default, if family is omitted addresses will be interpreted

as IPv4 addresses. The hashsize value is the initial hash size to use and

defaults to 1024. The maxelem value is the maximum number of elements which

can be stored in the set, it defaults to 65536.

The net f ilt er tool searches for a network prefix which is the most specific, it

tries to find the smallest block of addresses that match.

Example 4.9. Creat e an IP Set f or IP Addresses

To create an IP set for IP addresses, make use of the hash:ip set type as follows:

~]# ipset create my-addresses hash:ip

Once the set is created, entries can be added as follows:

~]# ipset add my-addresses 10.10.10.0

If additional options such as netmask and timeout are required, they must be specified

when the set is created. For example:

~]# ipset create my-busy-addresses hash:ip maxelem 24 netmask 28

timeout 100

The maxelem option restricts to total number of elements in the set, thus conserving

memory space.

The timeout option means that elements will only exist in the set for the number of

seconds specified. For example:

~]# ipset add my-busy-addresses 192.168.60.0 timeout 100

The following output shows the time counting down:

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~]# ipset list my-busy-addresses

Name: my-busy-addresses

Type: hash:ip

Header: family inet hashsize 1024 maxelem 24 netmask 28 timeout 100

Size in memory: 8300

References: 0

Members:

192.168.60.0 timeout 90

~]# ipset list my-busy-addresses

Name: my-busy-addresses

Type: hash:ip

Header: family inet hashsize 1024 maxelem 24 netmask 28 timeout 100

Size in memory: 8300

References: 0

Members:

192.168.60.0 timeout 83

The element will be removed from the set when the timeout period ends.

See the ipset(8) manual page for more examples.

4.5.5. Additional Resources

The following sources of information provide additional resources regarding firewalld.

4.5.5.1. Installed Documentation

firewalld(1) man page — Describes command options for firewalld.

firewalld.conf(5) man page — Contains information to configure firewalld.

firewalld-applet(1) man page — Describes settings for the f irewall-applet tool.

firewall-cmd(1) man page — Describes command options for the firewalld

command-line client.

firewall-config(1) man page — Describes settings for the f irewall-conf ig tool.

firewall-offline-cmd(1) man page — Describes command options for the

firewalld offline command-line client.

firewalld.icmptype(5) man page — Describes XML configuration files for ICMP

filtering.

firewalld.ipset(5) man page — Describes XML configuration files for the firewalld

IP sets.

firewalld.service(5) man page — Describes XML configuration files for f irewalld

service.

firewalld.zone(5) man page — Describes XML configuration files for firewalld zone

configuration.

firewalld.direct(5) man page — Describes the firewalld direct interface

configuration file.

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firewalld.lockdown-whitelist(5) man page — Describes the firewalld lockdown

whitelist configuration file.

firewall.richlanguage(5) man page — Describes the firewalld rich language rule

syntax.

firewalld.zones(5) man page — General description of what zones are and how to

configure them.

firewalld.dbus(5) man page — Describes the D-Bus interface of firewalld.

4.5.5.2. Online Documentation

http://www.firewalld.org/ — firewalld home page.

4.6. Securing DNS Traffic with DNSSEC

4.6.1. Introduction to DNSSEC

DNSSEC is a set of Domain Name System Security Extensions (DNSSEC) that enables a DNS

client to authenticate and check the integrity of responses from a DNS nameserver in

order to verify their origin and to determine if they have been tampered with in transit.

4.6.2. Underst anding DNSSEC

For connecting over the Internet, a growing number of websites now offer the ability to

connect securely using HTTPS. However, before connecting to an HTTPS webserver, a DNS

lookup must be performed, unless you enter the IP address directly. These DNS lookups

are done insecurely and are subject to man-in-the-middle attacks due to lack of

authentication. In other words, a DNS client cannot have confidence that the replies that

appear to come from a given DNS nameserver are authentic and have not been tampered

with. More importantly, a recursive nameserver cannot be sure that the records it obtains

from other nameservers are genuine. The DNS protocol did not provide a mechanism for

the client to ensure it was not subject to a man-in-the-middle attack. DNSSEC was

introduced to address the lack of authentication and integrity checks when resolving

domain names using DNS. It does not address the problem of confidentiality.

Publishing DNSSEC information involves digitally signing DNS resource records as well as

distributing public keys in such a way as to enable DNS resolvers to build a hierarchical

chain of trust. Digital signatures for all DNS resource records are generated and added to

the zone as digital signature resource records (RRSIG). The public key of a zone is added

as a DNSKEY resource record. To build the hierarchical chain, hashes of the DNSKEY are

published in the parent zone as Delegation of Signing (DS) resource records. To facilitate

proof of non-existence, the NextSECure (NSEC) and NSEC3 resource records are used. In a

DNSSEC signed zone, each resource record set (RRset) has a corresponding RRSIG

resource record. Note that records used for delegation to a child zone (NS and glue

records) are not signed; these records appear in the child zone and are signed there.

Processing DNSSEC information is done by resolvers that are configured with the root

zone public key. Using this key, resolvers can verify the signatures used in the root zone.

For example, the root zone has signed the DS record for .com. The root zone also serves

NS and glue records for the .com name servers. The resolver follows this delegation and

queries for the DNSKEY record of .com using these delegated name servers. The hash of

the DNSKEY record obtained should match the DS record in the root zone. If so, the

resolver will trust the obtained DNSKEY for .com. In the .com zone, the RRSIG records are

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created by the .com DNSKEY. This process is repeated similarly for delegations within

.com, such as redhat.com. Using this method, a validating DNS resolver only needs to be

configured with one root key while it collects many DNSKEYs from around the world during

its normal operation. If a cryptographic check fails, the resolver will return SERVFAIL to the

application.

DNSSEC has been designed in such a way that it will be completely invisible to

applications not supporting DNSSEC. If a non-DNSSEC application queries a DNSSEC

capable resolver, it will receive the answer without any of these new resource record

types such as RRSIG. However, the DNSSEC capable resolver will still perform all

cryptographic checks, and will still return a SERVFAIL error to the application if it detects

malicious DNS answers. DNSSEC protects the integrity of the data between DNS servers

(authoritative and recursive), it does not provide security between the application and the

resolver. Therefore, it is important that the applications are given a secure transport to

their resolver. The easiest way to accomplish that is to run a DNSSEC capable resolver on

localhost and use 127.0.0.1 in /etc/resolv.conf. Alternatively a VPN connection to a

remote DNS server could be used.

Understanding the Hotspot Problem

Wi-Fi Hotspots or VPNs rely on “DNS lies”: Captive portals tend to hijack DNS in order to

redirect users to a page where they are required to authenticate (or pay) for the Wi-Fi

service. Users connecting to a VPN often need to use an “internal only” DNS server in

order to locate resources that do not exist outside the corporate network. This requires

additional handling by software. For example, dnssec-t rigger can be used to detect if a

Hotspot is hijacking the DNS queries and unbound can act as a proxy nameserver to

handle the DNSSEC queries.

Choosing a DNSSEC Capable Recursive Resolver

To deploy a DNSSEC capable recursive resolver, either BIND or unbound can be used.

Both enable DNSSEC by default and are configured with the DNSSEC root key. To enable

DNSSEC on a server, either will work however the use of unbound is preferred on mobile

devices, such as notebooks, as it allows the local user to dynamically reconfigure the

DNSSEC overrides required for Hotspots when using dnssec-t rigger, and for VPNs when

using Libreswan. The unbound daemon further supports the deployment of DNSSEC

exceptions listed in the etc/unbound/*.d/ directories which can be useful to both

servers and mobile devices.

4.6.3. Underst anding Dnssec-trigger

Once unbound is installed and configured in /etc/resolv.conf, all DNS queries from

applications are processed by unbound. dnssec-t rigger only reconfigures the unbound

resolver when triggered to do so. This mostly applies to roaming client machines, such as

laptops, that connect to different Wi-Fi networks. The process is as follows:

Net workManager “triggers” dnssec-t rigger when a new DNS server is obtained

through DHCP.

Dnssec-t rigger then performs a number of tests against the server and decides

whether or not it properly supports DNSSEC.

If it does, then dnssec-t rigger reconfigures unbound to use that DNS server as a

forwarder for all queries.

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If the tests fail, dnssec-t rigger will ignore the new DNS server and try a few available

fall-back methods.

If it determines that an unrestricted port 53 (UDP and TCP) is available, it will tell

unbound to become a full recursive DNS server without using any forwarder.

If this is not possible, for example because port 53 is blocked by a firewall for

everything except reaching the network's DNS server itself, it will try to use DNS to port

80, or TLS encapsulated DNS to port 443. Servers running DNS on port 80 and 443 can

be configured in /etc/dnssec-trigger/dnssec-trigger.conf. Commented out

examples should be available in the default configuration file.

If these fall-back methods also fail, dnssec-t rigger offers to either operate

insecurely, which would bypass DNSSEC completely, or run in “cache only” mode where

it will not attempt new DNS queries but will answer for everything it already has in the

cache.

Wi-Fi Hotspots increasingly redirect users to a sign-on page before granting access to the

Internet. During the probing sequence outlined above, if a redirection is detected, the

user is prompted to ask if a login is required to gain Internet access. The dnssec-trigger

daemon continues to probe for DNSSEC resolvers every ten seconds. See Section 4.6.8,

“Using Dnssec-trigger” for information on using the dnssec-t rigger graphical utility.

4.6.4. VPN Supplied Domains and Name Servers

Some types of VPN connections can convey a domain and a list of nameservers to use for

that domain as part of the VPN tunnel setup. On Red Hat Ent erprise Linux, this is

supported by Net workManager. This means that the combination of unbound, dnssec-

t rigger, and Net workManager can properly support domains and name servers

provided by VPN software. Once the VPN tunnel comes up, the local unbound cache is

flushed for all entries of the domain name received, so that queries for names within the

domain name are fetched fresh from the internal name servers reached using the VPN.

When the VPN tunnel is terminated, the unbound cache is flushed again to ensure any

queries for the domain will return the public IP addresses, and not the previously obtained

private IP addresses. See Section 4.6.11, “Configuring DNSSEC Validation for Connection

Supplied Domains”.

4.6.5. Recommended Naming Practices

Red Hat recommends that both static and transient names match the fully-qualified domain

name (FQDN) used for the machine in DNS, such as host.example.com.

The Internet Corporation for Assigned Names and Numbers (ICANN) sometimes adds

previously unregistered Top-Level Domains (such as .yourcompany) to the public register.

Therefore, Red Hat strongly recommends that you do not use a domain name that is not

delegated to you, even on a private network, as this can result in a domain name that

resolves differently depending on network configuration. As a result, network resources

can become unavailable. Using domain names that are not delegated to you also makes

DNSSEC more difficult to deploy and maintain, as domain name collisions require manual

configuration to enable DNSSEC validation. See the ICANN FAQ on domain name collision

for more information on this issue.

4.6.6. Underst anding T rust Anchors

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In a hierarchical cryptographic system, a trust anchor is an authoritative entity which is

assumed to be trustworthy. For example, in X.509 architecture, a root certificate is a trust

anchor from which a chain of trust is derived. The trust anchor must be put in the

possession of the trusting party beforehand to make path validation possible.

In the context of DNSSEC, a trust anchor consists of a DNS name and public key (or hash of

the public key) associated with that name. It is expressed as a base 64 encoded key. It is

similar to a certificate in that it is a means of exchanging information, including a public

key, which can be used to verify and authenticate DNS records. RFC 4033 defines a trust

anchor as a configured DNSKEY RR or DS RR hash of a DNSKEY RR. A validating security-

aware resolver uses this public key or hash as a starting point for building the

authentication chain to a signed DNS response. In general, a validating resolver will have

to obtain the initial values of its trust anchors through some secure or trusted means

outside the DNS protocol. Presence of a trust anchor also implies that the resolver should

expect the zone to which the trust anchor points to be signed.

4.6.7. Inst alling DNSSEC

4.6.7.1. Installing unbound

In order to validate DNS using DNSSEC locally on a machine, it is necessary to install the

DNS resolver unbound (or bind ). It is only necessary to install dnssec-t rigger on mobile

devices. For servers, unbound should be sufficient although a forwarding configuration for

the local domain might be required depending on where the server is located (LAN or

Internet). dnssec-t rigger will currently only help with the global public DNS zone.

Net workManager, dhclient , and VPN applications can often gather the domain list (and

nameserver list as well) automatically, but not dnssec-t rigger nor unbound.

To install unbound enter the following command as the root user:

~]# yum install unbound

4.6.7.2. Checking if unbound is Running

To determine whether the unbound daemon is running, enter the following command:

~]$ systemctl status unbound

unbound.service - Unbound recursive Domain Name Server

Loaded: loaded (/usr/lib/systemd/system/unbound.service; disabled)

Active: active (running) since Wed 2013-03-13 01:19:30 CET; 6h ago

The systemctl status command will report unbound as Active: inactive (dead) if the

unbound service is not running.

4.6.7.3. Starting unbound

To start the unbound daemon for the current session, enter the following command as the

root user:

~]# systemctl start unbound

Run the systemctl enable command to ensure that unbound starts up every time the

system boots:

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~]# systemctl enable unbound

The unbound daemon allows configuration of local data or overrides using the following

directories:

The /etc/unbound/conf.d directory is used to add configurations for a specific domain

name. This is used to redirect queries for a domain name to a specific DNS server. This

is often used for sub-domains that only exist within a corporate WAN.

The /etc/unbound/keys.d directory is used to add trust anchors for a specific domain

name. This is required when an internal-only name is DNSSEC signed, but there is no

publicly existing DS record to build a path of trust. Another use case is when an internal

version of a domain is signed using a different DNSKEY than the publicly available

name outside the corporate WAN.

The /etc/unbound/local.d directory is used to add specific DNS data as a local

override. This can be used to build blacklists or create manual overrides. This data will

be returned to clients by unbound, but it will not be marked as DNSSEC signed.

Net workManager, as well as some VPN software, may change the configuration

dynamically. These configuration directories contain commented out example entries. For

further information see the unbound.conf(5) man page.

4.6.7.4. Installing Dnssec-trigger

The dnssec-t rigger application runs as a daemon, dnssec-triggerd. To install dnssec-

t rigger enter the following command as the root user:

~]# yum install dnssec-trigger

4.6.7.5. Checking if the Dnssec-trigger Daemon is Running

To determine whether dnssec-triggerd is running, enter the following command:

~]$ systemctl status dnssec-triggerd

systemctl status dnssec-triggerd.service

dnssec-triggerd.service - Reconfigure local DNS(SEC) resolver on network

change

Loaded: loaded (/usr/lib/systemd/system/dnssec-triggerd.service;

enabled)

Active: active (running) since Wed 2013-03-13 06:10:44 CET; 1h 41min

ago

The systemctl status command will report dnssec-triggerd as Active: inactive

(dead) if the dnssec-triggerd daemon is not running. To start it for the current session

enter the following command as the root user:

~]# systemctl start dnssec-triggerd

Run the systemctl enable command to ensure that dnssec-triggerd starts up every

time the system boots:

~]# systemctl enable dnssec-triggerd

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4.6.8. Using Dnssec-trigger

The dnssec-t rigger application has a GNOME panel utility for displaying DNSSEC probe

results and for performing DNSSEC probe requests on demand. To start the utility, press

the Super key to enter the Activities Overview, type DNSSEC and then press Enter. An

icon resembling a ships anchor is added to the message tray at the bottom of the screen.

Press the round blue notification icon in the bottom right of the screen to reveal it. Right

click the anchor icon to display a pop-up menu.

In normal operations unbound is used locally as the name server, and resolv.conf

points to 127.0.0.1. When you click OK on the Hotspot Sign-On panel this is changed.

The DNS servers are queried from Net wo rkManager and put in resolv.conf. Now you

can authenticate on the Hotspot's sign-on page. The anchor icon shows a big red

exclamation mark to warn you that DNS queries are being made insecurely. When

authenticated, dnssec-t rigger should automatically detect this and switch back to secure

mode, although in some cases it cannot and the user has to do this manually by selecting

Reprobe.

Dnssec-t rigger does not normally require any user interaction. Once started, it works in

the background and if a problem is encountered it notifies the user by means of a pop-up

text box. It also informs unbound about changes to the resolv.conf file.

4.6.9. Using dig Wit h DNSSEC

To see whether DNSSEC is working, one can use various command line tools. The best

tool to use is the dig command from the bind-utils package. Other tools that are useful are

drill from the ldns package and unbound-ho st from the unbound package. The old DNS

utilities nslookup and ho st are obsolete and should not be used.

To send a query requesting DNSSEC data using dig, the option +dnssec is added to the

command, for example:

~]$ dig +dnssec whitehouse.gov

; <<>> DiG 9.9.3-rl.13207.22-P2-RedHat-9.9.3-4.P2.el7 <<>> +dnssec

whitehouse.gov

;; global options: +cmd

;; Got answer:

;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 21388

;; flags: qr rd ra ad; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:

; EDNS: version: 0, flags: do; udp: 4096

;; QUESTION SECTION:

;whitehouse.gov. IN A

;; ANSWER SECTION:

whitehouse.gov. 20 IN A 72.246.36.110

whitehouse.gov. 20 IN RRSIG A 7 2 20 20130825124016 20130822114016 8399

whitehouse.gov. BB8VHWEkIaKpaLprt3hq1GkjDROvkmjYTBxiGhuki/BJn3PoIGyrftxR

HH0377I0Lsybj/uZv5hL4UwWd/lw6Gn8GPikqhztAkgMxddMQ2IARP6p

wbMOKbSUuV6NGUT1WWwpbi+LelFMqQcAq3Se66iyH0Jem7HtgPEUE1Zc 3oI=

;; Query time: 227 msec

;; SERVER: 127.0.0.1#53(127.0.0.1)

;; WHEN: Thu Aug 22 22:01:52 EDT 2013

;; MSG SIZE rcvd: 233

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In addition to the A record, an RRSIG record is returned which contains the DNSSEC

signature, as well as the inception time and expiration time of the signature. The unbound

server indicated that the data was DNSSEC authenticated by returning the ad bit in the

flags: section at the top.

If DNSSEC validation fails, the dig command would return a SERVFAIL error:

~]$ dig badsign-a.test.dnssec-tools.org

; <<>> DiG 9.9.3-rl.156.01-P1-RedHat-9.9.3-3.P1.el7 <<>> badsign-

a.test.dnssec-tools.org

;; global options: +cmd

;; Got answer:

;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 1010

;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:

; EDNS: version: 0, flags:; udp: 4096

;; QUESTION SECTION:

;badsign-a.test.dnssec-tools.org. IN A

;; Query time: 1284 msec

;; SERVER: 127.0.0.1#53(127.0.0.1)

;; WHEN: Thu Aug 22 22:04:52 EDT 2013

;; MSG SIZE rcvd: 60]

To request more information about the failure, DNSSEC checking can be disabled by

specifying the +cd option to the dig command:

~]$ dig +cd +dnssec badsign-a.test.dnssec-tools.org

; <<>> DiG 9.9.3-rl.156.01-P1-RedHat-9.9.3-3.P1.el7 <<>> +cd +dnssec

badsign-a.test.dnssec-tools.org

;; global options: +cmd

;; Got answer:

;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 26065

;; flags: qr rd ra cd; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:

; EDNS: version: 0, flags: do; udp: 4096

;; QUESTION SECTION:

;badsign-a.test.dnssec-tools.org. IN A

;; ANSWER SECTION:

badsign-a.test.dnssec-tools.org. 49 IN A 75.119.216.33

badsign-a.test.dnssec-tools.org. 49 IN RRSIG A 5 4 86400 20130919183720

20130820173720 19442 test.dnssec-tools.org.

E572dLKMvYB4cgTRyAHIKKEvdOP7tockQb7hXFNZKVbfXbZJOIDREJrr

zCgAfJ2hykfY0yJHAlnuQvM0s6xOnNBSvc2xLIybJdfTaN6kSR0YFdYZ

n2NpPctn2kUBn5UR1BJRin3Gqy20LZlZx2KD7cZBtieMsU/IunyhCSc0 kYw=

;; Query time: 1 msec

;; SERVER: 127.0.0.1#53(127.0.0.1)

;; WHEN: Thu Aug 22 22:06:31 EDT 2013

;; MSG SIZE rcvd: 257

Often, DNSSEC mistakes manifest themselves by bad inception or expiration time,

although in this example, the people at www.dnssec-tools.org have mangled this RRSIG

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signature on purpose, which we would not be able to detect by looking at this output

manually. The error will show in the output of systemctl status unbound and the

unbound daemon logs these errors to syslog as follows:

Aug 22 22:04:52 laptop unbound: [3065:0] info: validation failure

badsign-a.test.dnssec-tools.org. A IN

An example using unbound-host:

~]$ unbound-host -C /etc/unbound/unbound.conf -v whitehouse.gov

whitehouse.gov has address 184.25.196.110 (secure)

whitehouse.gov has IPv6 address 2600:1417:11:2:8800::fc4 (secure)

whitehouse.gov has IPv6 address 2600:1417:11:2:8000::fc4 (secure)

whitehouse.gov mail is handled by 105 mail1.eop.gov. (secure)

whitehouse.gov mail is handled by 110 mail5.eop.gov. (secure)

whitehouse.gov mail is handled by 105 mail4.eop.gov. (secure)

whitehouse.gov mail is handled by 110 mail6.eop.gov. (secure)

whitehouse.gov mail is handled by 105 mail2.eop.gov. (secure)

whitehouse.gov mail is handled by 105 mail3.eop.gov. (secure)

4.6.10. Sett ing up Hotspot Detect ion Infrastructure for Dnssec-

trigger

When connecting to a network, dnssec-t rigger attempts to detect a Hotspot. A Hotspot is

generally a device that forces user interaction with a web page before they can use the

network resources. The detection is done by attempting to download a specific fixed web

page with known content. If there is a Hotspot, then the content received will not be as

expected.

To set up a fixed web page with known content that can be used by dnssec-t rigger to

detect a Hotspot, proceed as follows:

1. Set up a web server on some machine that is publicly reachable on the Internet.

See the Web Servers chapter in the Red Hat Enterprise Linux 7 System

Administrator's Guide. .

2. Once you have the server running, publish a static page with known content on it.

The page does not need to be a valid HTML page. For example, you could use a

plain-text file named hotspot.txt that contains only the string OK. Assuming your

server is located at example.com and you published your hotspot.txt file in the

web server document_root/static/ sub-directory, then the address to your static

web page would be example.com/static/hotspot.txt. See the DocumentRoot

directive in the Web Servers chapter in the Red Hat Enterprise Linux 7 System

Administrator's Guide.

3. Add the following line to the /etc/dnssec-trigger/dnssec-trigger.conf file:

url: "http://example.com/static/hotspot.txt OK"

This command adds a URL that is probed using HTTP (port 80). The first part is the

URL that will be resolved and the page that will be downloaded. The second part of

the command is the text string that the downloaded webpage is expected to

contain.

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For more information on the configuration options see the man page dnssec-

trigger.conf(8).

4.6.11. Configuring DNSSEC Validat ion for Connect ion Supplied

Domains

By default, forward zones with proper nameservers are automatically added into unbound

by dnssec-t rigger for every domain provided by any connection, except Wi-Fi

connections through Net workManager. By default, all forward zones added into unbound

are DNSSEC validated.

The default behavior for validating forward zones can be altered, so that all forward zones

will not be DNSSEC validated by default. To do this, change the

validate_connection_provided_zones variable in the dnssec-t rigger configuration file

/etc/dnssec.conf. As root user, open and edit the line as follows:

validate_connection_provided_zones=no

The change is not done for any existing forward zones, but only for future forward zones.

Therefore if you want to disable DNSSEC for the current provided domain, you need to

reconnect.

4.6.11.1. Configuring DNSSEC Validation for Wi-Fi Supplied Domains

Adding forward zones for Wi-Fi provided zones can be enabled. To do this, change the

add_wifi_provided_zones variable in the dnssec-t rigger configuration file,

/etc/dnssec.conf. As root user, open and edit the line as follows:

add_wifi_provided_zones=yes

The change is not done for any existing forward zones, but only for future forward zones.

Therefore, if you want to enable DNSSEC for the current Wi-Fi provided domain, you need

to reconnect (restart) the Wi-Fi connection.

Warning

Turning o n the addition of Wi-Fi provided domains as forward zones into unbound

may have security implications such as:

1. A Wi-Fi access point can intentionally provide you a domain through DHCP for

which it does not have authority and route all your DNS queries to its DNS

servers.

2. If you have the DNSSEC validation of forward zones turned off, the Wi-Fi

provided DNS servers can spoof the IP address for domain names from the

provided domain without you knowing it.

4.6.12. Addit ional Resources

The following are resources which explain more about DNSSEC.

4.6.12.1. Installed Documentation

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dnssec-trigger(8) man page — Describes command options for dnssec-triggerd,

dnssec-t rigger-cont rol and dnssec-t rigger-panel.

dnssec-trigger.conf(8) man page — Describes the configuration options for

dnssec-triggerd.

unbound(8) man page — Describes the command options for unbound, the DNS

validating resolver.

unbound.conf(5) man page — Contains information on how to configure unbound.

resolv.conf(5) man page — Contains information that is read by the resolver

routines.

4.6.12.2. Online Documentation

ht t p://t o ols.iet f .o rg/ht ml/rf c40 33

RFC 4033 DNS Security Introduction and Requirements.

ht t p://www.dnssec.net /

A website with links to many DNSSEC resources.

ht t p://www.dnssec-deplo yment .o rg/

The DNSSEC Deployment Initiative, sponsored by the Department for Homeland

Security, contains a lot of DNSSEC information and has a mailing list to discuss

DNSSEC deployment issues.

ht t p://www.int ernet societ y.org/deplo y360 /dnssec/co mmunit y/

The Internet Society's “Deploy 360” initiative to stimulate and coordinate DNSSEC

deployment is a good resource for finding communities and DNSSEC activities

worldwide.

ht t p://www.unbound.net /

This document contains general information about the unbound DNS service.

ht t p://www.nlnet labs.nl/pro ject s/dnssec-t rigger/

This document contains general information about dnssec-t rigger.

4.7. Securing Virtual Private Networks (VPNs)

In Red Hat Enterprise Linux 7, a Virtual Private Network (VPN) can be configured using the

IPsec tunneling protocol which is supported by the Libreswan application. Libreswan is a

fork of the Openswan application and examples in documentation should be

interchangeable. The Net wo rkManager IPsec plug-in is called NetworkManager-

libreswan. Users of GNOME Shell should install the NetworkManager-libreswan-gnome

package, which has NetworkManager-libreswan as a dependency. Note that the

NetworkManager-libreswan-gnome package is only available from the Optional channel. See

Enabling Supplementary and Optional Repositories.

Libreswan is an open source, user space IPsec implementation available in Red Hat

Enterprise Linux 7. It uses the Internet key exchange (IKE) protocol. IKE version 1 and 2

are implemented as a user-level daemon. Manual key establishment is also possible

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through ip xfrm commands, however this is not recommended. Libreswan interfaces

with the Linux kernel using netlink to transfer the encryption keys. Packet encryption and

decryption happen in the Linux kernel.

Libreswan uses the network security services (NSS) cryptographic library, which is

required for Federal Information Processing Standard (FIPS) security compliance.

Important

IPsec, implemented by Libreswan, is the only VPN technology recommend for use

in Red Hat Enterprise Linux 7. Do not use any other VPN technology without

understanding the risks of doing so.

4.7.1. IPsec VPN Using Libreswan

To install Libreswan, issue the following command as root:

~]# yum install libreswan

To check that Libreswan is installed, issue the following command:

~]$ yum info libreswan

After a new installation of Libreswan the NSS database should be initialized as part of the

install process. However, should you need to start a new database, first remove the old

database as follows:

~]# rm /etc/ipsec.d/*db

Then, to initialize a new NSS database, issue the following command as root:

~]# ipsec initnss

Initializing NSS database

See 'man pluto' if you want to protect the NSS database with a password

If you do not want to use a password for NSS, just press Enter twice when prompted for

the password. If you do enter a password then you will have to re-enter it every time

Libreswan is started, such as every time the system is booted.

To start the ipsec daemon provided by Libreswan, issue the following command as root:

~]# systemctl start ipsec

To confirm that the daemon is now running:

~]$ systemctl status ipsec

ipsec.service - Internet Key Exchange (IKE) Protocol Daemon for IPsec

Loaded: loaded (/usr/lib/systemd/system/ipsec.service; disabled)

Active: active (running) since Wed 2013-08-21 12:14:12 CEST; 18s ago

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To ensure that Libreswan will start when the system starts, issue the following command

as root:

~]# systemctl enable ipsec

Configure any intermediate as well as host-based firewalls to permit the ipsec service.

See Section 4.5, “Using Firewalls” for information on firewalls and allowing specific

services to pass through. Libreswan requires the firewall to allow the following packets:

UDP port 500 for the Internet Key Exchange (IKE) protocol

UDP port 4500 for IKE NAT-Traversal

Protocol 50 for Encapsulated Security Payload (ESP) IPsec packets

Protocol 51 for Authenticated Header (AH) IPsec packets (uncommon)

We present three examples of using Libreswan to set up an IPsec VPN. The first

example is for connecting two hosts together so that they may communicate securely.

The second example is connecting two sites together to form one network. The third

example is supporting roaming users, known as road warriors in this context.

4.7.2. VPN Configurations Using Libreswan

Libreswan does not use the terms “source” or “destination”. Instead, it uses the terms

“left” and “right” to refer to end points (the hosts). This allows the same configuration to

be used on both end points in most cases, although most administrators use “left” for the

local host and “right” for the remote host.

There are three commonly used methods for authentication of endpoints:

Pre-Shared Keys (PSK) is the simplest authentication method. PSK's should consist of

random characters and have a length of at least 20 characters. Due to the dangers of

non-random and short PSKs, this method is not available when the system is running in

FIPS mode.

Raw RSA keys are commonly used for static host-to-host or subnet-to-subnet IPsec

configurations. The hosts are manually configured with each other's public RSA key.

This method does not scale well when dozens or more hosts all need to setup IPsec

tunnels to each other.

X.509 certificates are commonly used for large scale deployments where there are

many hosts that need to connect to a common IPsec gateway. A central certificate

authority (CA) is used to sign RSA certificates for hosts or users. This central CA is

responsible for relaying trust, including the revocations of individual hosts or users.

4.7.3. Host-T o-Host VPN Using Libreswan

To configure Libreswan to create a host-to-host IPsec VPN, between two hosts referred

to as “left” and “right”, enter the following commands as root on both of the hosts (“left”

and “right”) to create new raw RSA key pairs:

~]# ipsec newhostkey --configdir /etc/ipsec.d \

--output /etc/ipsec.d/www.example.com.secrets

Generated RSA key pair using the NSS database

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This generates an RSA key pair for the host. The process of generating RSA keys can take

many minutes, especially on virtual machines with low entropy.

To view the public key, issue the following command as root on either of the hosts. For

example, to view the public key on the “left” host, run:

~]# ipsec showhostkey --left

ipsec showhostkey loading secrets from "/etc/ipsec.secrets"

ipsec showhostkey loading secrets from

"/etc/ipsec.d/www.example.com.secrets"

ipsec showhostkey loaded private key for keyid: PPK_RSA:AQOjAKLlL

# rsakey AQOjAKLlL

leftrsasigkey=0sAQOjAKLlL4a7YBv [...]

You will need this key to add to the configuration file as explained below.

The secret part is stored in /etc/ipsec.d/*.db files, also called the “NSS database”.

To make a configuration file for this host-to-host tunnel, the lines leftrsasigkey= and

rightrsasigkey= from above, are added to a custom configuration file placed in the

/etc/ipsec.d/ directory. To enable Libreswan to read the custom configurations files,

use an editor running as root to edit the main configuration file, /etc/ipsec.conf, and

enable the following line by removing the # comment character so that it looks as follows:

include /etc/ipsec.d/*.conf

Using an editor running as root, create a file with a suitable name in the following format:

/etc/ipsec.d/my_host-to-host.conf

Edit the file as follows:

conn mytunnel

leftid=@west.example.com

left=192.1.2.23

leftrsasigkey=0sAQOrlo+hOafUZDlCQmXFrje/oZm [...]

W2n417C/4urYHQkCvuIQ==

rightid=@east.example.com

right=192.1.2.45

rightrsasigkey=0sAQO3fwC6nSSGgt64DWiYZzuHbc4 [...] D/v8t5YTQ==

authby=rsasig

# load and initiate automatically

auto=start

You can use the identical configuration file on both left and right hosts. They will auto-

detect if they are “left” or “right”. If one of the hosts is a mobile host, which implies the IP

address is not known in advance, then on the mobile host use %defaultroute as its IP

address. This will pick up the dynamic IP address automatically. On the static host that

accepts connections from incoming mobile hosts, specify the mobile host using %any for

its IP address.

Ensure the leftrsasigkey value is obtained from the “left” host and the rightrsasigkey

value is obtained from the “right” host.

Restart ipsec to ensure it reads the new configuration:

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~]# systemctl restart ipsec

Issue the following command as root to load the IPsec tunnel:

~]# ipsec auto --add mytunnel

To open the tunnel, issue the following command as root, on the left or the right side:

~]# ipsec auto --up mytunnel

4.7.3.1. Verify Host-T o-Host VPN Using Libreswan

The IKE negotiation takes place on UDP port 500. IPsec packets show up as

Encapsulated Security Payload (ESP) packets. When the VPN connection needs to pass

through a NAT router, the ESP packets are encapsulated in UDP packets on port 4500.

To verify that packets are being sent through the VPN tunnel, issue a command as root in

the following format:

~]# tcpdump -n -i interface esp or udp port 500 or udp port 4500

00:32:32.632165 IP 192.1.2.45 > 192.1.2.23:

ESP(spi=0x63ad7e17,seq=0x1a), length 132

00:32:32.632592 IP 192.1.2.23 > 192.1.2.45:

ESP(spi=0x4841b647,seq=0x1a), length 132

00:32:32.632592 IP 192.0.2.254 > 192.0.1.254: ICMP echo reply, id 2489,

seq 7, length 64

00:32:33.632221 IP 192.1.2.45 > 192.1.2.23:

ESP(spi=0x63ad7e17,seq=0x1b), length 132

00:32:33.632731 IP 192.1.2.23 > 192.1.2.45:

ESP(spi=0x4841b647,seq=0x1b), length 132

00:32:33.632731 IP 192.0.2.254 > 192.0.1.254: ICMP echo reply, id 2489,

seq 8, length 64

00:32:34.632183 IP 192.1.2.45 > 192.1.2.23:

ESP(spi=0x63ad7e17,seq=0x1c), length 132

00:32:34.632607 IP 192.1.2.23 > 192.1.2.45:

ESP(spi=0x4841b647,seq=0x1c), length 132

00:32:34.632607 IP 192.0.2.254 > 192.0.1.254: ICMP echo reply, id 2489,

seq 9, length 64

00:32:35.632233 IP 192.1.2.45 > 192.1.2.23:

ESP(spi=0x63ad7e17,seq=0x1d), length 132

00:32:35.632685 IP 192.1.2.23 > 192.1.2.45:

ESP(spi=0x4841b647,seq=0x1d), length 132

00:32:35.632685 IP 192.0.2.254 > 192.0.1.254: ICMP echo reply, id 2489,

seq 10, length 64

Where interface is the interface known to carry the traffic. To end the capture with

t cpdump, press Ctrl+C.

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Note

The t cpdump commands interacts a little unexpectedly with IPsec. It only sees the

outgoing encrypted packet, not the outgoing plaintext packet. It does see the

encrypted incoming packet, as well as the decrypted incoming packet. If possible,

run t cpdump on a router between the two machines and not on one of the

endpoints itself.

4.7.4. Sit e-to-Site VPN Using Libreswan

In order for Libreswan to create a site-to-site IPsec VPN, joining together two networks,

an IPsec tunnel is created between two hosts, endpoints, which are configured to permit

traffic from one or more subnets to pass through. They can therefore be thought of as

gateways to the remote portion of the network. The configuration of the site-to-site VPN

only differs from the host-to-host VPN in that one or more networks or subnets must be

specified in the configuration file.

To configure Libreswan to create a site-to-site IPsec VPN, first configure a host-to-host

IPsec VPN as described in Section 4.7.3, “Host-To-Host VPN Using Libreswan” and then

copy or move the file to a file with a suitable name, such as /etc/ipsec.d/my_site-to-

site.conf. Using an editor running as root, edit the custom configuration file

/etc/ipsec.d/my_site-to-site.conf as follows:

conn mysubnet

also=mytunnel

leftsubnet=192.0.1.0/24

rightsubnet=192.0.2.0/24

conn mysubnet6

also=mytunnel

connaddrfamily=ipv6

leftsubnet=2001:db8:0:1::/64

rightsubnet=2001:db8:0:2::/64

conn mytunnel

auto=start

leftid=@west.example.com

left=192.1.2.23

leftrsasigkey=0sAQOrlo+hOafUZDlCQmXFrje/oZm [...]

W2n417C/4urYHQkCvuIQ==

rightid=@east.example.com

right=192.1.2.45

rightrsasigkey=0sAQO3fwC6nSSGgt64DWiYZzuHbc4 [...] D/v8t5YTQ==

authby=rsasig

To bring the tunnels up, restart Libreswan or manually load and initiate all the

connections using the following commands as root:

~]# ipsec auto --add mysubnet

~]# ipsec auto --add mysubnet6

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~]# ipsec auto --add mytunnel

~]# ipsec auto --up mysubnet

104 "mysubnet" #1: STATE_MAIN_I1: initiate

003 "mysubnet" #1: received Vendor ID payload [Dead Peer Detection]

003 "mytunnel" #1: received Vendor ID payload [FRAGMENTATION]

106 "mysubnet" #1: STATE_MAIN_I2: sent MI2, expecting MR2

108 "mysubnet" #1: STATE_MAIN_I3: sent MI3, expecting MR3

003 "mysubnet" #1: received Vendor ID payload [CAN-IKEv2]

004 "mysubnet" #1: STATE_MAIN_I4: ISAKMP SA established

{auth=OAKLEY_RSA_SIG cipher=aes_128 prf=oakley_sha group=modp2048}

117 "mysubnet" #2: STATE_QUICK_I1: initiate

004 "mysubnet" #2: STATE_QUICK_I2: sent QI2, IPsec SA established tunnel

mode {ESP=>0x9414a615 <0x1a8eb4ef xfrm=AES_128-HMAC_SHA1 NATOA=none

NATD=none DPD=none}

~]# ipsec auto --up mysubnet6

003 "mytunnel" #1: received Vendor ID payload [FRAGMENTATION]

117 "mysubnet" #2: STATE_QUICK_I1: initiate

004 "mysubnet" #2: STATE_QUICK_I2: sent QI2, IPsec SA established tunnel

mode {ESP=>0x06fe2099 <0x75eaa862 xfrm=AES_128-HMAC_SHA1 NATOA=none

NATD=none DPD=none}

~]# ipsec auto --up mytunnel

104 "mytunnel" #1: STATE_MAIN_I1: initiate

003 "mytunnel" #1: received Vendor ID payload [Dead Peer Detection]

003 "mytunnel" #1: received Vendor ID payload [FRAGMENTATION]

106 "mytunnel" #1: STATE_MAIN_I2: sent MI2, expecting MR2

108 "mytunnel" #1: STATE_MAIN_I3: sent MI3, expecting MR3

003 "mytunnel" #1: received Vendor ID payload [CAN-IKEv2]

004 "mytunnel" #1: STATE_MAIN_I4: ISAKMP SA established

{auth=OAKLEY_RSA_SIG cipher=aes_128 prf=oakley_sha group=modp2048}

117 "mytunnel" #2: STATE_QUICK_I1: initiate

004 "mytunnel" #2: STATE_QUICK_I2: sent QI2, IPsec SA established tunnel

mode {ESP=>0x9414a615 >0x1a8eb4ef xfrm=AES_128-HMAC_SHA1 NATOA=none

NATD=none DPD=none}

4.7.4.1. Verify Site-to-Site VPN Using Libreswan

Verifying that packets are being sent through the VPN tunnel is the same procedure as

explained in Section 4.7.3.1, “Verify Host-To-Host VPN Using Libreswan”.

4.7.5. Sit e-to-Site Single T unnel VPN Using Libreswan

Often, when a site-to-site tunnel is built, the gateways need to communicate with each

other using their internal IP addresses instead of their public IP addresses. This can be

accomplished using a single tunnel. If the left host, with host name west, has internal IP

address 192.0.1.254 and the right host, with host name east, has internal IP address

192.0.2.254, the following configuration using a single tunnel can be used:

conn mysubnet

leftid=@west.example.com

leftrsasigkey=0sAQOrlo+hOafUZDlCQmXFrje/oZm [...]

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W2n417C/4urYHQkCvuIQ==

left=192.1.2.23

leftsourceip=192.0.1.254

leftsubnet=192.0.1.0/24

rightid=@east.example.com

rightrsasigkey=0sAQO3fwC6nSSGgt64DWiYZzuHbc4 [...] D/v8t5YTQ==

right=192.1.2.45

rightsourceip=192.0.2.254

rightsubnet=192.0.2.0/24

auto=start

authby=rsasig

4.7.6. Subnet Extrusion Using Libreswan

IPsec is often deployed in a hub-and-spoke architecture. Each leaf node has an IP range

that is part of a larger range. Leaves communicate with each other through the hub. This

is called subnet extrusion. In the example below, we configure the head office with

10.0.0.0/8 and two branches that use a smaller /24 subnet.

At the head office:

conn branch1

left=1.2.3.4

leftid=@headoffice

leftsubnet=0.0.0.0/0

leftrsasigkey=0sA[...]

right=5.6.7.8

rightid=@branch1

rightsubnet=10.0.1.0/24

rightrsasigkey=0sAXXXX[...]

auto=start

authby=rsasig

conn branch2

left=1.2.3.4

leftid=@headoffice

leftsubnet=0.0.0.0/0

leftrsasigkey=0sA[...]

right=10.11.12.13

rightid=@branch2

rightsubnet=10.0.2.0/24

rightrsasigkey=0sAYYYY[...]

auto=start

authby=rsasig

At the “branch1” office, we use the same connection. Additionally, we use a pass-through

connection to exclude our local LAN traffic from being sent through the tunnel:

conn branch1

left=1.2.3.4

leftid=@headoffice

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leftsubnet=0.0.0.0/0

leftrsasigkey=0sA[...]

right=10.11.12.13

rightid=@branch2

rightsubnet=10.0.1.0/24

rightrsasigkey=0sAYYYY[...]

auto=start

authby=rsasig

conn passthrough

left=1.2.3.4

right=0.0.0.0

leftsubnet=10.0.1.0/24

rightsubnet=10.0.1.0/24

authby=never

type=passthrough

auto=route

4.7.7. Road Warrior Application Using Libreswan

Road Warriors are traveling users with mobile clients with a dynamically assigned IP

address, such as laptops. These are authenticated using certificates.

On the server:

conn roadwarriors

left=1.2.3.4

# if access to the LAN is given, enable this

#leftsubnet=10.10.0.0/16

leftcert=gw.example.com

leftid=%fromcert

right=%any

# trust our own Certificate Agency

rightca=%same

# allow clients to be behind a NAT router

rightsubnet=vhost:%priv,%no

authby=rsasig

# load connection, don't initiate

auto=add

# kill vanished roadwarriors

dpddelay=30

dpdtimeout=120

dpdaction=%clear

On the mobile client, the Road Warrior's device, we need to use a slight variation of the

above configuration:

conn roadwarriors

# pick up our dynamic IP

left=%defaultroute

leftcert=myname.example.com

leftid=%fromcert

# right can also be a DNS hostname

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right=1.2.3.4

# if access to the remote LAN is required, enable this

#rightsubnet=10.10.0.0/16

# trust our own Certificate Agency

rightca=%same

authby=rsasig

# Initiate connection

auto=start

4.7.8. Road Warrior Application Using Libreswan and XAUT H with X.509

Libreswan offers a method to natively assign IP address and DNS information to roaming

VPN clients as the connection is established by using the XAUTH IPsec extension. XAUTH

can be deployed using PSK or X.509 certificates. Deploying using X.509 is more secure.

Client certificates can be revoked by a certificate revocation list or by Online Certificate

Status Protocol (OCSP). With X.509 certificates, individual clients cannot impersonate the

server. With a PSK, also called Group Password, this is theoretically possible.

XAUTH requires the VPN client to additionally identify itself with a user name and

password. For One time Passwords (OTP), such as Google Authenticator or RSA SecureID

tokens, the one-time token is appended to the user password.

There are three possible back ends for XAUTH:

xauthby=pam

This uses the configuration in /etc/pam.d/pluto to authenticate the user. Pam

can be configured to use various back ends by itself. It can use the system

account user-password scheme, an LDAP directory, a RADIUS server or a custom

password authentication module.

xauthby=file

This uses the configuration file /etc/ipsec.d/passwd (not to be confused with

/etc/ipsec.d/nsspassword). The format of this file is similar to the Apache

.htpasswd file and the Apache htpasswd command can be used to create

entries in this file. However, after the user name and password, a third column is

required with the connection name of the IPsec connection used, for example

when using a conn remoteusers to offer VPN to remove users, a password file

entry should look as follows:

user1:$apr1$MIwQ3DHb$1I69LzTnZhnCT2DPQmAOK.:remoteusers

NOTE: when using the htpasswd command, the connection name has to be

manually added after the user:password part on each line.

xauthby=alwaysok

The server will always pretend the XAUTH user and password combination was

correct. The client still has to specify a user name and a password, although the

server ignores these. This should only be used when users are already

identified by X.509 certificates, or when testing the VPN without needing an

XAUTH back end.

An example configuration with X.509 certificates:

conn xauth-rsa

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auto=add

authby=rsasig

pfs=no

rekey=no

left=ServerIP

leftcert=vpn.example.com

#leftid=%fromcert

leftid=vpn.example.com

leftsendcert=always

leftsubnet=0.0.0.0/0

rightaddresspool=10.234.123.2-10.234.123.254

right=%any

rightrsasigkey=%cert

modecfgdns1=1.2.3.4

modecfgdns2=8.8.8.8

modecfgdomain=example.com

modecfgbanner="Authorized Access is allowed"

leftxauthserver=yes

rightxauthclient=yes

leftmodecfgserver=yes

rightmodecfgclient=yes

modecfgpull=yes

xauthby=pam

dpddelay=30

dpdtimeout=120

dpdaction=clear

ike_frag=yes

# for walled-garden on xauth failure

# xauthfail=soft

#leftupdown=/custom/_updown

When xauthfail is set to soft, instead of hard, authentication failures are ignored, and

the VPN is setup as if the user authenticated properly. A custom updown script can be

used to check for the environment variable XAUTH_FAILED. Such users can then be

redirected, for example, using ipt ables DNAT, to a “walled garden” where they can

contact the administrator or renew a paid subscription to the service.

VPN clients use the modecfgdomain value and the DNS entries to redirect queries for the

specified domain to these specified nameservers. This allows roaming users to access

internal-only resources using the internal DNS names.

If leftsubnet is not 0.0.0.0/0, split tunneling configuration requests are sent

automatically to the client. For example, when using leftsubnet=10.0.0.0/8, the VPN

client would only send traffic for 10.0.0.0/8 through the VPN.

4.7.9. Additional Resources

The following sources of information provide additional resources regarding Libreswan

and the ipsec daemon.

4.7.9.1. Installed Documentation

ipsec(8) man page — Describes command options for ipsec.

ipsec.conf(5) man page — Contains information on configuring ipsec.

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ipsec.secrets(5) man page — Describes the format of the ipsec.secrets file.

ipsec_auto(8) man page — Describes the use of the aut o command line client for

manipulating Libreswan IPsec connections established using automatic exchanges of

keys.

ipsec_rsasigkey(8) man page — Describes the tool used to generate RSA signature

keys.

/usr/share/doc/libreswan-version/README.nss — Describes the commands for

using raw RSA keys and certificates with the NSS crypto library used with the

Libreswan pluto daemon.

4.7.9.2. Online Documentation

ht t ps://libreswan.org

The website of the upstream project.

ht t p://www.mozilla.o rg/pro ject s/securit y/pki/nss/

Network Security Services (NSS) project.

4.8. Using OpenSSL

OpenSSL is a library that provides cryptographic protocols to applications. The o penssl

command line utility enables using the cryptographic functions from the shell. It includes

an interactive mode.

The openssl command line utility has a number of pseudo-commands to provide

information on the commands that the version of openssl installed on the system

supports. The pseudo-commands list-standard-commands, list-message-digest-

commands, and list-cipher-commands output a list of all standard commands, message

digest commands, or cipher commands, respectively, that are available in the present

openssl utility.

The pseudo-commands list-cipher-algorithms and list-message-digest-

algorithms list all cipher and message digest names. The pseudo-command list-

public-key-algorithms lists all supported public key algorithms. For example, to list the

supported public key algorithms, issue the following command:

~]$ openssl list-public-key-algorithms

The pseudo-command no-command-name tests whether a command-name of the specified

name is available. Intended for use in shell scripts. See man openssl(1) for more

information.

4.8.1. Creat ing and Managing Encryption Keys

With OpenSSL, public keys are derived from the corresponding private key. Therefore the

first step, once having decided on the algorithm, is to generate the private key. In these

examples the private key is referred to as privkey.pem. For example, to create an RSA

private key using default parameters, issue the following command:

~]$ openssl genpkey -algorithm RSA -out privkey.pem

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The RSA algorithm supports the following options:

rsa_keygen_bits:numbits — The number of bits in the generated key. If not specified

1024 is used.

rsa_keygen_pubexp:value — The RSA public exponent value. This can be a large

decimal value, or a hexadecimal value if preceded by 0x. The default value is 65537.

For example, to create a 2048 bit RSA private key using 3 as the public exponent, issue

the following command:

~]$ openssl genpkey -algorithm RSA -out privkey.pem -pkeyopt

rsa_keygen_bits:2048 \ -pkeyopt rsa_keygen_pubexp:3

To encrypt the private key as it is output using 128 bit AES and the passphrase “hello”,

issue the following command:

~]$ openssl genpkey -algorithm RSA -out privkey.pem -aes-128-cbc -pass

pass:hello

See man genpkey(1) for more information on generating private keys.

4.8.2. Generating Cert ificates

To generate a certificate using OpenSSL, it is necessary to have a private key available.

In these examples the private key is referred to as privkey.pem. If you have not yet

generated a private key, see Section 4.8.1, “Creating and Managing Encryption Keys”

To have a certificate signed by a certificate authority (CA), it is necessary to generate a

certificate and then send it to a CA for signing. This is referred to as a certificate signing

request. See Section 4.8.2.1, “Creating a Certificate Signing Request” for more information.

The alternative is to create a self-signed certificate. See Section 4.8.2.2, “Creating a Self-

signed Certificate” for more information.

4.8.2.1. Creating a Certif icate Signing Request

To create a certificate for submission to a CA, issue a command in the following format:

~]$ openssl req -new -key privkey.pem -out cert.csr

This will create an X.509 certificate called cert.csr encoded in the default privacy-

enhanced electronic mail (PEM) format. The name PEM is derived from “Privacy

Enhancement for Internet Electronic Mail” described in RFC 1424. To generate a certificate

file in the alternative DER format, use the -outform DER command option.

After issuing the above command, you will be prompted for information about you and the

organization in order to create a distinguished name (DN) for the certificate. You will need

the following information:

The two letter country code for your country

The full name of your state or province

City or Town

The name of your organization

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The name of the unit within your organization

Your name or the host name of the system

Your email address

The req(1) man page describes the PKCS# 10 certificate request and generating utility.

Default settings used in the certificate creating process are contained within the

/etc/pki/tls/openssl.cnf file. See man openssl.cnf(5) for more information.

4.8.2.2. Creating a Self -signed Certif icate

To generate a self-signed certificate, valid for 366 days, issue a command in the following

format:

~]$ openssl req -new -x509 -key privkey.pem -out selfcert.pem -days 366

4.8.2.3. Creating a Certif icate Using a Makef ile

The /etc/pki/tls/certs/ directory contains a Makefile which can be used to create

certificates using the make command. To view the usage instructions, issue a command as

follows:

~]$ make -f /etc/pki/tls/certs/Makefile

Alternatively, change to the directory and issue the make command as follows:

~]$ cd /etc/pki/tls/certs/

~]$ make

See the make(1) man page for more information.

4.8.3. Verifying Cert ificates

A certificate signed by a CA is referred to as a trusted certificate. A self-signed certificate

is therefore an untrusted certificate. The verify utility uses the same SSL and S/MIME

functions to verify a certificate as is used by OpenSSL in normal operation. If an error is

found it is reported and then an attempt is made to continue testing in order to report any

other errors.

To verify multiple individual X.509 certificates in PEM format, issue a command in the

following format:

~]$ openssl verify cert1.pem cert2.pem

To verify a certificate chain the leaf certificate must be in cert.pem and the intermediate

certificates which you do not trust must be directly concatenated in untrusted.pem. The

trusted root CA certificate must be either among the default CA listed in

/etc/pki/tls/certs/ca-bundle.crt or in a cacert.pem file. Then, to verify the chain,

issue a command in the following format:

~]$ openssl verify -untrusted untrusted.pem -CAfile cacert.pem cert.pem

See man verify(1) for more information.

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Important

Verification of signatures using the MD5 hash algorithm is disabled in Red Hat

Enterprise Linux 7 due to insufficient strength of this algorithm. Always use strong

algorithms such as SHA256.

4.8.4. Encrypt ing and Decrypting a File

For encrypting (and decrypting) files with OpenSSL, either the pkeyutl or enc built-in

commands can be used. With pkeyutl, RSA keys are used to perform the encrypting and

decrypting, whereas with enc, symmetric algorithms are used.

Using RSA Keys

To encrypt a file called plaintext, issue a command as follows:

~]$ openssl pkeyutl -in plaintext -out cyphertext -inkey privkey.pem

The default format for keys and certificates is PEM. If required, use the -keyform DER

option to specify the DER key format.

To specify a cryptographic engine, use the -engine option as follows:

~]$ openssl pkeyutl -in plaintext -out cyphertext -inkey privkey.pem -

engine id

Where id is the ID of the cryptographic engine. To check the availability of an engine,

issue the following command:

~]$ openssl engine -t

To sign a data file called plaintext, issue a command as follows:

~]$ openssl pkeyutl -sign -in plaintext -out sigtext -inkey privkey.pem

To verify a signed data file and to extract the data, issue a command as follows:

~]$ openssl pkeyutl -verifyrecover -in sig -inkey key.pem

To verify the signature, for example using a DSA key, issue a command as follows:

~]$ openssl pkeyutl -verify -in file -sigfile sig -inkey key.pem

The pkeyutl(1) manual page describes the public key algorithm utility.

Using Symmetric Algorithms

To list available symmetric encryption algorithms, execute the enc command with an

unsupported option, such as -l:

~]$ openssl enc -l

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To specify an algorithm, use its name as an option. For example, to use the aes-128-cbc

algorithm, use the following syntax:

openssl enc -aes-128-cbc

To encrypt a file called plaintext using the aes-128-cbc algorithm, enter the following

command:

~]$ openssl enc -aes-128-cbc -in plaintext -out plaintext.aes-128-cbc

To decrypt the file obtained in the previous example, use the -d option as in the following

example:

~]$ openssl enc -aes-128-cbc -d -in plaintext.aes-128-cbc -out

plaintext

Important

The enc command does not properly support AEAD ciphers, and the ecb mode is not

considered secure. For best results, do not use other modes than cbc, cfb, ofb, or

ctr.

4.8.5. Generating Message Digests

The dgst command produces the message digest of a supplied file or files in

hexadecimal form. The command can also be used for digital signing and verification. The

message digest command takes the following form:

openssl dgst algorithm -out filename -sign private-key

Where algorithm is one of md5|md4|md2|sha1|sha|mdc2|ripemd160|dss1. At time of

writing, the SHA1 algorithm is preferred. If you need to sign or verify using DSA, then the

dss1 option must be used together with a file containing random data specified by the -

rand option.

To produce a message digest in the default Hex format using the sha1 algorithm, issue

the following command:

~]$ openssl dgst sha1 -out digest-file

To digitally sign the digest, using a private key privekey.pem, issue the following

command:

~]$ openssl dgst sha1 -out digest-file -sign privkey.pem

See man dgst(1) for more information.

4.8.6. Generating Password Hashes

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The passwd command computes the hash of a password. To compute the hash of a

password on the command line, issue a command as follows:

~]$ openssl passwd password

The -crypt algorithm is used by default.

To compute the hash of a password from standard input, using the MD5 based BSD

algorithm 1, issue a command as follows:

~]$ openssl passwd -1 password

The -apr1 option specifies the Apache variant of the BSD algorithm.

To compute the hash of a password stored in a file, and using a salt xx, issue a command

as follows:

~]$ openssl passwd -salt xx -in password-file

The password is sent to standard output and there is no -out option to specify an output

file. The -table will generate a table of password hashes with their corresponding clear

text password.

See man sslpasswd(1) for more information and examples.

4.8.7. Generating Random Dat a

To generate a file containing random data, using a seed file, issue the following command:

~]$ openssl rand -out rand-file -rand seed-file

Multiple files for seeding the random data process can be specified using the colon, :, as

a list separator.

See man rand(1) for more information.

4.8.8. Benchmarking Your System

To test the computational speed of a system for a given algorithm, issue a command in

the following format:

~]$ openssl speed algorithm

where algorithm is one of the supported algorithms you intended to use. To list the

available algorithms, type openssl speed and then press tab.

4.8.9. Configuring OpenSSL

OpenSSL has a configuration file /etc/pki/tls/openssl.cnf, referred to as the master

configuration file, which is read by the OpenSSL library. It is also possible to have

individual configuration files for each application. The configuration file contains a number

of sections with section names as follows: [ section_name ]. Note the first part of the

file, up until the first [ section_name ], is referred to as the default section. When

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OpenSSL is searching for names in the configuration file the named sections are

searched first. All OpenSSL commands use the master OpenSSL configuration file unless

an option is used in the command to specify an alternative configuration file. The

configuration file is explained in detail in the config(5) man page.

Two RFCs explain the contents of a certificate file. They are:

Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL)

Profile

Updates to the Internet X.509 Public Key Infrastructure Certificate and Certificate

Revocation List (CRL) Profile

4.9. Using stunnel

The st unnel program is an encryption wrapper between a client and a server. It listens

on the port specified in its configuration file, encrypts the communitation with the client,

and forwards the data to the original daemon listening on its usual port. This way, you can

secure any service that itself does not support any type of encryption, or improve the

security of a service that uses a type of encryption that you want to avoid for security

reasons, such as SSL versions 2 and 3, affected by the POODLE SSL vulnerability (CVE-

2014-3566). See https://access.redhat.com/solutions/1234773 for details. CUPS is an

example of a component that does not provide a way to disable SSL in its own

configuration.

4.9.1. Inst alling st unnel

Install the stunnel package by running the following command as root:

~]# yum install stunnel

4.9.2. Configuring st unnel as a T LS Wrapper

To configure st unnel, follow these steps:

1. You need a valid certificate for st unnel regardless of what service you use it with.

If you do not have a suitable certificate, you can apply to a Certificate Authority to

obtain one, or you can create a self-signed certificate.

Warning

Always use certificates signed by a Certificate Authority for servers running

in a production environment. Self-signed certificates are only appropriate for

testing purposes or private networks.

See Section 4.8.2.1, “Creating a Certificate Signing Request” for more information

about certificates granted by a Certificate Authority. On the other hand, to create a

self-signed certificate for st unnel, enter the /etc/pki/tls/certs/ directory and

type the following command as root:

certs]# make stunnel.pem

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Answer all of the questions to complete the process.

2. When you have a certificate, create a configuration file for st unnel. It is a text file

in which every line specifies an option or the beginning of a service definition. You

can also keep comments and empty lines in the file to improve its legibility, where

comments start with a semicolon.

The stunnel RPM package contains the /etc/stunnel/ directory, in which you can

store the configuration file. Although st unnel does not require any special format

of the file name or its extension, use /etc/stunnel/stunnel.conf. The following

content configures st unnel as a TLS wrapper:

cert = /etc/pki/tls/certs/stunnel.pem

; Allow only TLS, thus avoiding SSL

sslVersion = TLSv1

chroot = /var/run/stunnel

setuid = nobody

setgid = nobody

pid = /stunnel.pid

socket = l:TCP_NODELAY=1

socket = r:TCP_NODELAY=1

[service_name]

accept = port

connect = port

TIMEOUTclose = 0

Alternatively, you can avoid SSL by replacing the line containing sslVersion =

TLSv1 with the following lines:

options = NO_SSLv2

options = NO_SSLv3

The purpose of the options is as follows:

cert — the path to your certificate

sslVersion — the version of SSL; note that you can use TLS here even though

SSL and TLS are two independent cryptographic protocols

chroot — the changed root directory in which the stunnel process runs, for

greater security

setuid, setgid — the user and group that the st unnel process runs as; nobody

is a restricted system account

pid — the file in which st unnel saves its process ID, relative to chroot

socket — local and remote socket options; in this case, disable Nagle's algorithm

to improve network latency

[service_name] — the beginning of the service definition; the options used

below this line apply to the given service only, whereas the options above affect

st unnel globally

accept — the port to listen on

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connect — the port to connect to; this must be the port that the service you are

securing uses

TIMEOUTclose — how many seconds to wait for the close_notify alert from the

client; 0 instructs st unnel not to wait at all

options — OpenSSL library options

Example 4.10. Securing CUPS

To configure stunnel as a TLS wrapper for CUPS, use the following values:

[cups]

accept = 632

connect = 631

Instead of 632, you can use any free port that you prefer. 631 is the port that

CUPS normally uses.

3. Create the chroot directory and give the user specified by the setuid option write

access to it. To do so, enter the following commands as root:

~]# mkdir /var/run/stunnel

~]# chown nobody:nobody /var/run/stunnel

This allows st unnel to create the PID file.

4. If your system is using firewall settings that disallow access to the new port,

change them accordingly. See Section 4.5.3.1.6, “Opening Ports in the Firewall” for

details.

5. When you have created the configuration file and the chroot directory, and when

you are sure that the specified port is accessible, you are ready to start using

st unnel.

4.9.3. Start ing, Stopping, and Restart ing st unnel

To start st unnel, enter the following command as root:

~]# stunnel /etc/stunnel/stunnel.conf

By default, st unnel uses /var/log/secure to log its output.

To terminate st unnel, kill the process by running the following command as root:

~]# kill `cat /var/run/stunnel/stunnel.pid`

If you edit the configuration file while st unnel is running, terminate st unnel and start it

again for your changes to take effect.

4.10. Encryption

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4.10.1. Using LUKS Disk Encryption

Linux Unified Key Setup-on-disk-format (or LUKS) allows you to encrypt partitions on your

Linux computer. This is particularly important when it comes to mobile computers and

removable media. LUKS allows multiple user keys to decrypt a master key, which is used

for the bulk encryption of the partition.

Overview of LUKS

What LUKS do es

LUKS encrypts entire block devices and is therefore well-suited for protecting

the contents of mobile devices such as removable storage media or laptop

disk drives.

The underlying contents of the encrypted block device are arbitrary. This

makes it useful for encrypting swap devices. This can also be useful with

certain databases that use specially formatted block devices for data storage.

LUKS uses the existing device mapper kernel subsystem.

LUKS provides passphrase strengthening which protects against dictionary

attacks.

LUKS devices contain multiple key slots, allowing users to add backup keys or

passphrases.

What LUKS do es not do:

LUKS is not well-suited for applications requiring many (more than eight) users

to have distinct access keys to the same device.

LUKS is not well-suited for applications requiring file-level encryption.

4.10.1.1. LUKS Implementation in Red Hat Enterprise Linux

Red Hat Enterprise Linux 7 utilizes LUKS to perform file system encryption. By default, the

option to encrypt the file system is unchecked during the installation. If you select the

option to encrypt your hard drive, you will be prompted for a passphrase that will be asked

every time you boot the computer. This passphrase "unlocks" the bulk encryption key that

is used to decrypt your partition. If you choose to modify the default partition table you can

choose which partitions you want to encrypt. This is set in the partition table settings.

The default cipher used for LUKS (see cryptsetup --help) is aes-cbc-essiv:sha256

(ESSIV - Encrypted Salt-Sector Initialization Vector). Note that the installation program,

Anaconda, uses by default XTS mode (aes-xts-plain64). The default key size for LUKS is

256 bits. The default key size for LUKS with Anaconda (XTS mode) is 512 bits. Ciphers

that are available are:

AES - Advanced Encryption Standard - FIPS PUB 197

Twofish (A 128-bit Block Cipher)

Serpent

cast5 - RFC 2144

cast6 - RFC 2612

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4.10.1.2. Manually Encrypting Directories

Warning

Following this procedure will remove all data on the partition that you are encrypting.

You WILL lose all your information! Make sure you backup your data to an external

source before beginning this procedure!

1. Enter runlevel 1 by typing the following at a shell prompt as root:

telinit 1

2. Unmount your existing /home:

umount /home

3. If the command in the previous step fails, use fuser to find processes hogging

/home and kill them:

fuser -mvk /home

4. Verify /home is no longer mounted:

grep home /proc/mounts

5. Fill your partition with random data:

shred -v --iterations=1 /dev/VG00/LV_home

This command proceeds at the sequential write speed of your device and may take

some time to complete. It is an important step to ensure no unencrypted data is

left on a used device, and to obfuscate the parts of the device that contain

encrypted data as opposed to just random data.

6. Initialize your partition:

cryptsetup --verbose --verify-passphrase luksFormat

/dev/VG00/LV_home

7. Open the newly encrypted device:

cryptsetup luksOpen /dev/VG00/LV_home home

8. Make sure the device is present:

ls -l /dev/mapper | grep home

9. Create a file system:

mkfs.ext3 /dev/mapper/home

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10. Mount the file system:

mount /dev/mapper/home /home

11. Make sure the file system is visible:

df -h | grep home

12. Add the following to the /etc/crypttab file:

home /dev/VG00/LV_home none

13. Edit the /etc/fstab file, removing the old entry for /home and adding the following

line:

/dev/mapper/home /home ext3 defaults 1 2

14. Restore default SELinux security contexts:

/sbin/restorecon -v -R /home

15. Reboot the machine:

shutdown -r now

16. The entry in the /etc/crypttab makes your computer ask your luks passphrase

on boot.

17. Log in as root and restore your backup.

You now have an encrypted partition for all of your data to safely rest while the computer

is off.

4.10.1.3. Add a New Passphrase to an Existing Device

Use the following command to add a new passphrase to an existing device:

cryptsetup luksAddKey device

After being prompted for any one of the existing passprases for authentication, you will be

prompted to enter the new passphrase.

4.10.1.4. Remove a Passphrase from an Existing Device

Use the following command to remove a passphrase from an existing device:

cryptsetup luksRemoveKey device

You will be prompted for the passphrase you want to remove and then for any one of the

remaining passphrases for authentication.

4.10.1.5. Creating Encrypted Block Devices in Anaconda

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You can create encrypted devices during system installation. This allows you to easily

configure a system with encrypted partitions.

To enable block device encryption, check the Encrypt System check box when selecting

automatic partitioning or the Encrypt check box when creating an individual partition,

software RAID array, or logical volume. After you finish partitioning, you will be prompted

for an encryption passphrase. This passphrase will be required to access the encrypted

devices. If you have pre-existing LUKS devices and provided correct passphrases for

them earlier in the install process the passphrase entry dialog will also contain a check

box. Checking this check box indicates that you would like the new passphrase to be

added to an available slot in each of the pre-existing encrypted block devices.

Note

Checking the Encrypt System check box on the Automatic Partitioning screen

and then choosing Create custom layout does not cause any block devices to be

encrypted automatically.

Note

You can use kickstart to set a separate passphrase for each new encrypted block

device.

4.10.1.6. Additional Resources

For additional information on LUKS or encrypting hard drives under Red Hat

Enterprise Linux 7 visit one of the following links:

LUKS home page

LUKS/cryptsetup FAQ

LUKS - Linux Unified Key Setup Wikipedia article

HOWTO: Creating an encrypted Physical Volume (PV) using a second hard drive and

pvmove

4.10.2. Creat ing GPG Keys

GPG is used to identify yourself and authenticate your communications, including those

with people you do not know. GPG allows anyone reading a GPG-signed email to verify its

authenticity. In other words, GPG allows someone to be reasonably certain that

communications signed by you actually are from you. GPG is useful because it helps

prevent third parties from altering code or intercepting conversations and altering the

message.

4.10.2.1. Creating GPG Keys in GNOME

To create a GPG Key in GNOME, follow these steps:

1. Install the Seahorse utility, which makes GPG key management easier:

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~]# yum install seahorse

2. To create a key, from the Applicat io ns → Accessories menu select Passwords

and Encrypt ion Keys, which starts the application Seahorse.

3. From the File menu select New and then PGP Key. Then click Continue.

4. Type your full name, email address, and an optional comment describing who you

are (for example: John C. Smith, jsmith@example.com, Software Engineer). Click

Create. A dialog is displayed asking for a passphrase for the key. Choose a strong

passphrase but also easy to remember. Click OK and the key is created.

Warning

If you forget your passphrase, you will not be able to decrypt the data.

To find your GPG key ID, look in the Key ID column next to the newly created key. In most

cases, if you are asked for the key ID, prepend 0x to the key ID, as in 0x6789ABCD. You

should make a backup of your private key and store it somewhere secure.

4.10.2.2. Creating GPG Keys in KDE

To create a GPG Key in KDE, follow these steps:

1. Start the KGpg program from the main menu by selecting Applicat io ns →

Ut ilit ies → Encryption To o l. If you have never used KGpg before, the program

walks you through the process of creating your own GPG keypair.

2. A dialog box appears prompting you to create a new key pair. Enter your name,

email address, and an optional comment. You can also choose an expiration time

for your key, as well as the key strength (number of bits) and algorithms.

3. Enter your passphrase in the next dialog box. At this point, your key appears in the

main KGpg window.

Warning

If you forget your passphrase, you will not be able to decrypt the data.

To find your GPG key ID, look in the Key ID column next to the newly created key. In most

cases, if you are asked for the key ID, prepend 0x to the key ID, as in 0x6789ABCD. You

should make a backup of your private key and store it somewhere secure.

4.10.2.3. Creating GPG Keys Using the Command Line

1. Use the following shell command:

~]$ gpg2 --gen-key

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This command generates a key pair that consists of a public and a private key.

Other people use your public key to authenticate and decrypt your communications.

Distribute your public key as widely as possible, especially to people who you know

will want to receive authentic communications from you, such as a mailing list.

2. A series of prompts directs you through the process. Press the Enter key to

assign a default value if desired. The first prompt asks you to select what kind of

key you prefer:

Please select what kind of key you want:

(1) RSA and RSA (default)

(2) DSA and Elgamal

(3) DSA (sign only)

(4) RSA (sign only)

Your selection?

In almost all cases, the default is the correct choice. An RSA/RSA key allows you not

only to sign communications, but also to encrypt files.

3. Choose the key size:

RSA keys may be between 1024 and 4096 bits long.

What keysize do you want? (2048)

Again, the default, 2048, is sufficient for almost all users, and represents an

extremely strong level of security.

4. Choose when the key will expire. It is a good idea to choose an expiration date

instead of using the default, which is none. If, for example, the email address on

the key becomes invalid, an expiration date will remind others to stop using that

public key.

Please specify how long the key should be valid.

0 = key does not expire

d = key expires in n days

w = key expires in n weeks

m = key expires in n months

y = key expires in n years

key is valid for? (0)

Entering a value of 1y, for example, makes the key valid for one year. (You may

change this expiration date after the key is generated, if you change your mind.)

5. Before the gpg2 application asks for signature information, the following prompt

appears:

Is this correct (y/N)?

Enter y to finish the process.

6. Enter your name and email address for your GPG key. Remember this process is

about authenticating you as a real individual. For this reason, include your real

name. If you choose a bogus email address, it will be more difficult for others to

find your public key. This makes authenticating your communications difficult. If you

are using this GPG key for self-introduction on a mailing list, for example, enter the

email address you use on that list.

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Use the comment field to include aliases or other information. (Some people use

different keys for different purposes and identify each key with a comment, such

as "Office" or "Open Source Projects.")

7. At the confirmation prompt, enter the letter O to continue if all entries are correct,

or use the other options to fix any problems. Finally, enter a passphrase for your

secret key. The gpg2 program asks you to enter your passphrase twice to ensure

you made no typing errors.

8. Finally, gpg2 generates random data to make your key as unique as possible.

Move your mouse, type random keys, or perform other tasks on the system during

this step to speed up the process. Once this step is finished, your keys are

complete and ready to use:

pub 1024D/1B2AFA1C 2005-03-31 John Q. Doe <jqdoe@example.com>

Key fingerprint = 117C FE83 22EA B843 3E86 6486 4320 545E 1B2A

FA1C

sub 1024g/CEA4B22E 2005-03-31 [expires: 2006-03-31]

9. The key fingerprint is a shorthand "signature" for your key. It allows you to confirm

to others that they have received your actual public key without any tampering. You

do not need to write this fingerprint down. To display the fingerprint at any time,

use this command, substituting your email address:

~]$ gpg2 --fingerprint jqdoe@example.com

Your "GPG key ID" consists of 8 hex digits identifying the public key. In the example

above, the GPG key ID is 1B2AFA1C. In most cases, if you are asked for the key ID,

prepend 0x to the key ID, as in 0x6789ABCD.

Warning

If you forget your passphrase, the key cannot be used and any data encrypted using

that key will be lost.

4.10.2.4. About Public Key Encryption

1. Wikipedia - Public Key Cryptography

2. HowStuffWorks - Encryption

4.10.3. Using openCryptoki for Public-Key Crypt ography

openCrypt o ki is a Linux implementation of PKCS#11, which is a Public-Key Cryptography

Standard that defines an application programming interface (API) to cryptographic devices

called tokens. Tokens may be implemented in hardware or software. This chapter

provides an overview of the way the o penCrypt o ki system is installed, configured, and

used in Red Hat Enterprise Linux 7.

4.10.3.1. Installing openCryptoki and Starting the Service

To install the basic openCrypt o ki packages on your system, including a software

implementation of a token for testing purposes, enter the following command as root:

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~]# yum install opencryptoki

Depending on the type of hardware tokens you intend to use, you may need to install

additional packages that provide support for your specific use case. For example, to obtain

support for Trusted Platform Module (TPM) devices, you need to install the opencryptoki-

tpmtok package.

See the Installing Packages section of the Red Hat Enterprise Linux 7 System

Administrator's Guide for general information on how to install packages using the Yum

package manager.

To enable the o penCrypt o ki service, you need to run the pkcsslotd daemon. Start the

daemon for the current session by executing the following command as root:

~]# systemctl start pkcsslotd

To ensure that the service is automatically started at boot time, enter the following

command:

~]# systemctl enable pkcsslotd

See the Managing Services with systemd chapter of the Red Hat Enterprise Linux 7

System Administrator's Guide for more information on how to use systemd targets to

manage services.

4.10.3.2. Configuring and Using openCryptoki

When started, the pkcsslotd daemon reads the

/etc/opencryptoki/opencryptoki.conf configuration file, which it uses to collect

information about the tokens configured to work with the system and about their slots.

The file defines the individual slots using key-value pairs. Each slot definition can contain a

description, a specification of the token library to be used, and an ID of the slot's

manufacturer. Optionally, the version of the slot's hardware and firmware may be defined.

See the opencryptoki.conf(5) manual page for a description of the file's format and for a

more detailed description of the individual keys and the values that can be assigned to

them.

To modify the behavior of the pkcsslotd daemon at run time, use the pkcsconf utility.

This tool allows you to show and configure the state of the daemon, as well as to list and

modify the currently configured slots and tokens. For example, to display information about

tokens, issue the following command (note that all non-root users that need to

communicate with the pkcsslotd daemon must be a part of the pkcs11 system group):

~]$ pkcsconf -t

See the pkcsconf(1) manual page for a list of arguments available with the pkcsconf tool.

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Warning

Keep in mind that only fully trusted users should be assigned membership in the

pkcs11 group, as all members of this group have the right to block other users of

the o penCrypt o ki service from accessing configured PKCS#11 tokens. All

members of this group can also execute arbitrary code with the privileges of any

other users of openCrypt oki.

4.10.4. Using Smart Cards to Supply Credentials t o OpenSSH

The smart card is a lightweight hardware security module in a USB stick, MicroSD, or

SmartCard form factor. It provides a remotely manageable secure key store. In Red Hat

Enterprise Linux 7, OpenSSH supports authentication using smart cards.

To use your smart card with OpenSSH, store the public key from the card to the

~/.ssh/authorized_keys file. Install the PKCS#11 library provided by the opensc package

on the client. PKCS#11 is a Public-Key Cryptography Standard that defines an application

programming interface (API) to cryptographic devices called tokens. enter the following

command as root:

~]# yum install opensc

To use smart cards that are not supported by opensc (CoolKey and CAC), install the

coolkey package by running the following command as root:

~]# yum install coolkey

4.10.4.1. Retrieving a Public Key f rom a Card

To list the keys on your card, use the ssh-keygen command. Specify the shared library

(OpenSC in the following example) with the -D directive.

~]$ ssh-keygen -D /usr/lib64/pkcs11/opensc-pkcs11.so

ssh-rsa AAAAB3NzaC1yc[...]+g4Mb9

4.10.4.2. Storing a Public Key on a Server

To enable authentication using a smart card on a remote server, transfer the public key to

the remote server. Do it by copying the retrieved string (key) and pasting it to the remote

shell, or by storing your key to a file (smartcard.pub in the following example) and using

the ssh-copy-id command:

~]$ SSH_COPY_ID_LEGACY=1 ssh-copy-id -i smartcard.pub user@hostname

user@hostname's password:

Number of key(s) added: 1

Now try logging into the machine, with: "ssh user@hostname"

and check to make sure that only the key(s) you wanted were added.

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Storing a public key without a private key file requires to use the SSH_COPY_ID_LEGACY=1

environment variable.

4.10.4.3. Authenticating to a Server with a Key on a Smart Card

OpenSSH can read your public key from a smart card and perform operations with your

private key without exposing the key itself. This means that the private key does not

leave the card. To connect to a remote server using your smart card for authentication,

enter the following command and enter the PIN protecting your card:

[localhost ~]$ ssh -I /usr/lib64/pkcs11/opensc-pkcs11.so hostname

Enter PIN for 'Test (UserPIN)':

[hostname ~]$

Replace the hostname with the actual host name to which you want to connect.

To save unnecessary typing next time you connect to the remote server, store the path

to the PKCS#11 library in your ~/.ssh/config file:

Host hostname

PKCS11Provider /usr/lib64/pkcs11/opensc-pkcs11.so

Connect by running the ssh command without any additional options:

[localhost ~]$ ssh hostname

Enter PIN for 'Test (UserPIN)':

[hostname ~]$

4.10.4.4. Using ssh-agent to Automate PIN Logging In

Set up environmental variables to start using ssh-agent. You can skip this step in most

cases because ssh-agent is already running in a typical session. Use the following

command to check whether you can connect to your authentication agent:

~]$ ssh-add -l

Could not open a connection to your authentication agent.

~]$ eval `ssh-agent`

To avoid writing your PIN every time you connect using this key, add the card to the agent

by running the following command:

~]$ ssh-add -s /usr/lib64/pkcs11/opensc-pkcs11.so

Enter PIN for 'Test (UserPIN)':

Card added: /usr/lib64/pkcs11/opensc-pkcs11.so

To remove the card from ssh-agent, use the following command:

~]$ ssh-add -e /usr/lib64/pkcs11/opensc-pkcs11.so

Card removed: /usr/lib64/pkcs11/opensc-pkcs11.so

4.10.4.5. Additional Resources

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Setting up your hardware or software token is described in the Smart Card support in Red

Hat Enterprise Linux 7 article.

4.10.5. T rusted and Encrypted Keys

Trusted and encrypted keys are variable-length symmetric keys generated by the kernel

that utilize the kernel keyring service. The fact that the keys never appear in user space

in an unencrypted form means that their integrity can be verified, which in turn means that

they can be used, for example, by the extended verification module (EVM) to verify and

confirm the integrity of a running system. User-level programs can only ever access the

keys in the form of encrypted blobs.

Trusted keys need a hardware component: the Trusted Platform Module (TPM) chip, which

is used to both create and encrypt (seal) the keys. The TPM seals the keys using a 2048-

bit RSA key called the storage root key (SRK).

In addition to that, trusted keys may also be sealed using a specific set of the TPM's

platform configuration register (PCR) values. The PCR contains a set of integrity-

management values that reflect the BIOS, boot loader, and operating system. This means

that PCR-sealed keys can only be decrypted by the TPM on the exact same system on

which they were encrypted. However, once a PCR-sealed trusted key is loaded (added to

a keyring), and thus its associated PCR values are verified, it can be updated with new (or

future) PCR values, so that a new kernel, for example, can be booted. A single key can

also be saved as multiple blobs, each with different PCR values.

Encrypted keys do not require a TPM, as they use the kernel AES encryption, which makes

them faster than trusted keys. Encrypted keys are created using kernel-generated

random numbers and encrypted by a master key when they are exported into user-space

blobs. This master key can be either a trusted key or a user key, which is their main

disadvantage — if the master key is not a trusted key, the encrypted key is only as

secure as the user key used to encrypt it.

4.10.5.1. Working with Keys

Prior to any operations with keys, relevant kernel modules need to be loaded. For trusted

keys, it is the t rust ed module, and for encrypted keys, it is the encrypt ed-keys module.

Use the following command as the root user to load both of these modules at once:

~]# modprobe trusted encrypted-keys

Trusted and encrypted keys can be created, loaded, exported, and updated using the

keyct l utility. For detailed information about using keyct l, see keyctl(1).

Note

In order to use a TPM (such as for creating and sealing trusted keys), it needs to be

enabled and active. This can be usually achieved through a setting in the machine's

BIOS or using the tpm_setactive command from the tpm-tools package of utilities.

Also, the T ro uSers application needs to be installed (the trousers package), and the

tcsd daemon, which is a part of the T rouSers suite, running to communicate with

the TPM.

To create a trusted key using a TPM, execute the keyctl command with the following

syntax:

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keyctl add trusted name "new keylength [options]" keyring

Using the above syntax, an example command can be constructed as follows:

~]$ keyctl add trusted kmk "new 32" @u

642500861

The above example creates a trusted key called kmk with the length of 32 bytes (256 bits)

and places it in the user keyring (@u). The keys may have a length of 32 to 128 bytes (256

to 1024 bits). Use the show subcommand to list the current structure of the kernel

keyrings:

~]$ keyctl show

Session Keyring

-3 --alswrv 500 500 keyring: _ses

97833714 --alswrv 500 -1 \_ keyring: _uid.1000

642500861 --alswrv 500 500 \_ trusted: kmk

The print subcommand outputs the encrypted key to the standard output. To export the

key to a user-space blob, use the pipe subcommand as follows:

~]$ keyctl pipe 642500861 > kmk.blob

To load the trusted key from the user-space blob, use the add command again with the

blob as an argument:

~]$ keyctl add trusted kmk "load `cat kmk.blob`" @u

268728824

The TPM-sealed trusted key can then be employed to create secure encrypted keys. The

following command syntax is used for generating encrypted keys:

~]$ keyctl add encrypted name "new [format] key-type:master-key-name

keylength" keyring

Based on the above syntax, a command for generating an encrypted key using the

already created trusted key can be constructed as follows:

~]$ keyctl add encrypted encr-key "new trusted:kmk 32" @u

159771175

To create an encrypted key on systems where a TPM is not available, use a random

sequence of numbers to generate a user key, which is then used to seal the actual

encrypted keys.

~]$ keyctl add user kmk-user "`dd if=/dev/urandom bs=1 count=32

2>/dev/null`" @u

427069434

Then generate the encrypted key using the random-number user key:

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~]$ keyctl add encrypted encr-key "new user:kmk-user 32" @u

1012412758

The list subcommand can be used to list all keys in the specified kernel keyring:

~]$ keyctl list @u

2 keys in keyring:

427069434: --alswrv 1000 1000 user: kmk-user

1012412758: --alswrv 1000 1000 encrypted: encr-key

Important

Keep in mind that encrypted keys that are not sealed by a master trusted key are

only as secure as the user master key (random-number key) used to encrypt them.

Therefore, the master user key should be loaded as securely as possible and

preferably early during the boot process.

4.10.5.2. Additional Resources

The following offline and online resources can be used to acquire additional information

pertaining to the use of trusted and encrypted keys.

Installed Documentation

keyctl(1) — Describes the use of the keyct l utility and its subcommands.

Online Documentation

Red Hat Enterprise Linux 7 SELinux User's and Administrator's Guide — The SELinux

User's and Administrator's Guide for Red Hat Enterprise Linux 7 describes the basic

principles of SELinux and documents in detail how to configure and use SELinux with

various services, such as the Apache HT T P Server.

https://www.kernel.org/doc/Documentation/security/keys-trusted-encrypted.txt — The

official documentation about the trusted and encrypted keys feature of the Linux kernel.

See Also

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Section A.2.4, “SSL/TLS” provides a concise description of the SSL and TLS protocols.

Section 4.8, “Using OpenSSL” describes, among other things, how to use OpenSSL to

create and manage keys, generate certificates, and encrypt and decrypt files.

4.12. Using MACsec (IEEE 802.1AE)

Media Access Control Security (MACsec) encrypts and authenticates all traffic in LANs

with the GCM-AES-128 algorithm. MACsec can protect not only your IP traffic, but also ARP

and neighbor discovery or DHCP. MACsec operates in the different layer than IPsec or SSL

and TLS. Combine MACsec with security protocols for other networking layers to take

advantage of different security guarantees that these standards provide.

See the MACsec: a different solution to encrypt network traffic article for more information

about the architecture of a MACsec network, use case scenarios, and configuration

examples.

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Chapter 5. System Auditing

The Linux Audit system provides a way to track security-relevant information on your

system. Based on pre-configured rules, Audit generates log entries to record as much

information about the events that are happening on your system as possible. This

information is crucial for mission-critical environments to determine the violator of the

security policy and the actions they performed. Audit does not provide additional security

to your system; rather, it can be used to discover violations of security policies used on

your system. These violations can further be prevented by additional security measures

such as SELinux.

The following list summarizes some of the information that Audit is capable of recording in

its log files:

Date and time, type, and outcome of an event.

Sensitivity labels of subjects and objects.

Association of an event with the identity of the user who triggered the event.

All modifications to Audit configuration and attempts to access Audit log files.

All uses of authentication mechanisms, such as SSH, Kerberos, and others.

Changes to any trusted database, such as /etc/passwd.

Attempts to import or export information into or from the system.

Include or exclude events based on user identity, subject and object labels, and other

attributes.

The use of the Audit system is also a requirement for a number of security-related

certifications. Audit is designed to meet or exceed the requirements of the following

certifications or compliance guides:

Controlled Access Protection Profile (CAPP)

Labeled Security Protection Profile (LSPP)

Rule Set Base Access Control (RSBAC)

National Industrial Security Program Operating Manual (NISPOM)

Federal Information Security Management Act (FISMA)

Payment Card Industry — Data Security Standard (PCI-DSS)

Security Technical Implementation Guides (STIG)

Audit has also been:

Evaluated by National Information Assurance Partnership (NIAP) and Best Security

Industries (BSI).

Certified to LSPP/CAPP/RSBAC/EAL4+ on Red Hat Enterprise Linux 5.

Certified to Operating System Protection Profile / Evaluation Assurance Level 4+

(OSPP/EAL4+) on Red Hat Enterprise Linux 6.

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Use Cases

Wat ching f ile access

Audit can track whether a file or a directory has been accessed, modified,

executed, or the file's attributes have been changed. This is useful, for example,

to detect access to important files and have an Audit trail available in case one of

these files is corrupted.

Mo nit oring syst em calls

Audit can be configured to generate a log entry every time a particular system

call is used. This can be used, for example, to track changes to the system time

by monitoring the settimeofday, clock_adjtime, and other time-related system

calls.

Recording commands run by a user

Audit can track whether a file has been executed, so rules can be defined to

record every execution of a particular command. For example, a rule can be

defined for every executable in the /bin directory. The resulting log entries can

then be searched by user ID to generate an audit trail of executed commands

per user.

Recording execut ion of syst em pat hnames

Aside from watching file access which translates a path to an inode at rule

invocation, Audit can now watch the execution of a path even if it does not exist at

rule invocation, or if the file is replaced after rule invocation. This allows rules to

continue to work after upgrading a program executable or before it is even

installed.

Recording securit y event s

The pam_faillock authentication module is capable of recording failed login

attempts. Audit can be set up to record failed login attempts as well, and provides

additional information about the user who attempted to log in.

Searching f o r events

Audit provides the ausearch utility, which can be used to filter the log entries

and provide a complete audit trail based on a number of conditions.

Running summary report s

The aurepo rt utility can be used to generate, among other things, daily reports

of recorded events. A system administrator can then analyze these reports and

investigate suspicious activity further.

Mo nit oring net wo rk access

The ipt ables and ebt ables utilities can be configured to trigger Audit events,

allowing system administrators to monitor network access.

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Note

System performance may be affected depending on the amount of information that

is collected by Audit.

5.1. Audit System Architecture

The Audit system consists of two main parts: the user-space applications and utilities, and

the kernel-side system call processing. The kernel component receives system calls from

user-space applications and filters them through one of the three filters: user, task, or exit.

Once a system call passes the exclude filter, it is sent through one of the aforementioned

filters, which, based on the Audit rule configuration, sends it to the Audit daemon for

further processing. Figure 5.1, “Audit System Architecture” illustrates this process.

Figure 5.1. Audit Syst em Archit ecture

The user-space Audit daemon collects the information from the kernel and creates entries

in a log file. Other Audit user-space utilities interact with the Audit daemon, the kernel

Audit component, or the Audit log files:

audisp — the Audit dispatcher daemon interacts with the Audit daemon and sends

events to other applications for further processing. The purpose of this daemon is to

provide a plug-in mechanism so that real-time analytical programs can interact with

Audit events.

audit ct l — the Audit control utility interacts with the kernel Audit component to

manage rules and to control a number of settings and parameters of the event

generation process.

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The remaining Audit utilities take the contents of the Audit log files as input and

generate output based on user's requirements. For example, the aurepo rt utility

generates a report of all recorded events.

5.2. Installing the audit Packages

In order to use the Audit system, you must have the audit packages installed on your

system. The audit packages (audit and audit-libs) are installed by default on Red Hat

Enterprise Linux 7. If you do not have these packages installed, execute the following

command as the root user to install Audit and the dependencies:

~]# yum install audit

5.3. Configuring the audit Service

The Audit daemon can be configured in the /etc/audit/auditd.conf file. This file

consists of configuration parameters that modify the behavior of the Audit daemon. Empty

lines and text following a hash sign (#) are ignored. For further details, see the

audit.conf(5) man page.

5.3.1. Configuring auditd for a Secure Environment

The default auditd configuration should be suitable for most environments. However, if

your environment has to meet strict security policies, the following settings are

suggested for the Audit daemon configuration in the /etc/audit/auditd.conf file:

lo g_f ile

The directory that holds the Audit log files (usually /var/log/audit/) should

reside on a separate mount point. This prevents other processes from

consuming space in this directory, and provides accurate detection of the

remaining space for the Audit daemon.

max_lo g_f ile

Specifies the maximum size of a single Audit log file, must be set to make full

use of the available space on the partition that holds the Audit log files.

max_lo g_f ile_act io n

Decides what action is taken once the limit set in max_log_file is reached,

should be set to keep_logs to prevent Audit log files from being overwritten.

space_lef t

Specifies the amount of free space left on the disk for which an action that is set

in the space_left_action parameter is triggered. Must be set to a number that

gives the administrator enough time to respond and free up disk space. The

space_left value depends on the rate at which the Audit log files are generated.

space_lef t _act ion

It is recommended to set the space_left_action parameter to email or exec

with an appropriate notification method.

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admin_space_lef t

Specifies the absolute minimum amount of free space for which an action that is

set in the admin_space_left_action parameter is triggered, must be set to a

value that leaves enough space to log actions performed by the administrator.

admin_space_lef t _act io n

Should be set to single to put the system into single-user mode and allow the

administrator to free up some disk space.

disk_f ull_act ion

Specifies an action that is triggered when no free space is available on the

partition that holds the Audit log files, must be set to halt or single. This

ensures that the system is either shut down or operating in single-user mode

when Audit can no longer log events.

disk_erro r_act io n

Specifies an action that is triggered in case an error is detected on the partition

that holds the Audit log files, must be set to syslog, single, or halt, depending

on your local security policies regarding the handling of hardware malfunctions.

f lush

Should be set to incremental_async. It works in combination with the freq

parameter, which determines how many records can be sent to the disk before

forcing a hard synchronization with the hard drive. The freq parameter should be

set to 100. These parameters assure that Audit event data is synchronized with

the log files on the disk while keeping good performance for bursts of activity.

The remaining configuration options should be set according to your local security policy.

5.4. Starting the audit Service

Once auditd is configured, start the service to collect Audit information and store it in the

log files. Execute the following command as the root user to start auditd:

~]# service auditd start

Note

The service command is the only way to correctly interact with the auditd daemon.

You need to use the service command so that the auid value is properly recorded.

You can use the systemctl command only for two actions: enable and status.

To configure auditd to start at boot time using the following command as the root user:

~]# systemctl enable auditd

A number of other actions can be performed on auditd using the service auditd

action command, where action can be one of the following:

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stop

Stops auditd.

restart

Restarts auditd.

reload o r force-reload

Reloads the configuration of audit d from the /etc/audit/auditd.conf file.

rotate

Rotates the log files in the /var/log/audit/ directory.

resume

Resumes logging of Audit events after it has been previously suspended, for

example, when there is not enough free space on the disk partition that holds the

Audit log files.

condrestart o r try-restart

Restarts audit d only if it is already running.

status

Displays the running status of audit d.

5.5. Defining Audit Rules

The Audit system operates on a set of rules that define what is to be captured in the log

files. The following types of Audit rules can be specified:

Cont rol rules

Allow the Audit system's behavior and some of its configuration to be modified.

File syst em rules

Also known as file watches, allow the auditing of access to a particular file or a

directory.

Syst em call rules

Allow logging of system calls that any specified program makes.

Audit rules can be set:

on the command line using the audit ct l utility. Note that these rules are not persistent

across reboots. For details, see Section 5.5.1, “Defining Audit Rules with audit ct l”

in the /etc/audit/audit.rules file. For details, see Section 5.5.3, “Defining Persistent

Audit Rules and Controls in the /etc/audit/audit.rules File”

5.5.1. Defining Audit Rules with audit ctl

The auditctl command allows you to control the basic functionality of the Audit system

and to define rules that decide which Audit events are logged.

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Note

All commands which interact with the Audit service and the Audit log files require

root privileges. Ensure you execute these commands as the root user. Additionally,

CAP_AUDIT_CONTROL is required to set up audit services and CAP_AUDIT_WRITE is

required to log user messages.

Defining Control Rules

The following are some of the control rules that allow you to modify the behavior of the

Audit system:

-b

sets the maximum amount of existing Audit buffers in the kernel, for example:

~]# auditctl -b 8192

-f

sets the action that is performed when a critical error is detected, for example:

~]# auditctl -f 2

The above configuration triggers a kernel panic in case of a critical error.

-e

enables and disables the Audit system or locks its configuration, for example:

~]# auditctl -e 2

The above command locks the Audit configuration.

-r

sets the rate of generated messages per second, for example:

~]# auditctl -r 0

The above configuration sets no rate limit on generated messages.

-s

reports the status of the Audit system, for example:

~]# auditctl -s

AUDIT_STATUS: enabled=1 flag=2 pid=0 rate_limit=0

backlog_limit=8192 lost=259 backlog=0

-l

lists all currently loaded Audit rules, for example:

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~]# auditctl -l

-w /etc/passwd -p wa -k passwd_changes

-w /etc/selinux -p wa -k selinux_changes

-w /sbin/insmod -p x -k module_insertion

⋮

-D

deletes all currently loaded Audit rules, for example:

~]# auditctl -D

No rules

Defining File Syst em Rules

To define a file system rule, use the following syntax:

auditctl -w path_to_file -p permissions -k key_name

where:

path_to_file is the file or directory that is audited.

permissions are the permissions that are logged:

r — read access to a file or a directory.

w — write access to a file or a directory.

x — execute access to a file or a directory.

a — change in the file's or directory's attribute.

key_name is an optional string that helps you identify which rule or a set of rules

generated a particular log entry.

Example 5.1. File Syst em Rules

To define a rule that logs all write access to, and every attribute change of, the

/etc/passwd file, execute the following command:

~]# auditctl -w /etc/passwd -p wa -k passwd_changes

Note that the string following the -k option is arbitrary.

To define a rule that logs all write access to, and every attribute change of, all the files

in the /etc/selinux/ directory, execute the following command:

~]# auditctl -w /etc/selinux/ -p wa -k selinux_changes

To define a rule that logs the execution of the /sbin/insmod command, which inserts a

module into the Linux kernel, execute the following command:

~]# auditctl -w /sbin/insmod -p x -k module_insertion

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Defining Syst em Call Rules

To define a system call rule, use the following syntax:

auditctl -a action,filter -S system_call -F field=value -k key_name

where:

action and filter specify when a certain event is logged. action can be either always or

never. filter specifies which kernel rule-matching filter is applied to the event. The rule-

matching filter can be one of the following: task, exit, user, and exclude. For more

information about these filters, see the beginning of Section 5.1, “Audit System

Architecture”.

system_call specifies the system call by its name. A list of all system calls can be

found in the /usr/include/asm/unistd_64.h file. Several system calls can be

grouped into one rule, each specified after its own -S option.

field=value specifies additional options that further modify the rule to match events

based on a specified architecture, group ID, process ID, and others. For a full listing of

all available field types and their values, see the auditctl(8) man page.

key_name is an optional string that helps you identify which rule or a set of rules

generated a particular log entry.

Example 5.2. Syst em Call Rules

To define a rule that creates a log entry every time the adjtimex or settimeofday

system calls are used by a program, and the system uses the 64-bit architecture,

execute the following command:

~]# auditctl -a always,exit -F arch=b64 -S adjtimex -S settimeofday -k

time_change

To define a rule that creates a log entry every time a file is deleted or renamed by a

system user whose ID is 1000 or larger, execute the following command:

~]# auditctl -a always,exit -S unlink -S unlinkat -S rename -S

renameat -F auid>=1000 -F auid!=4294967295 -k delete

Note that the -F auid!=4294967295 option is used to exclude users whose login UID is

not set.

It is also possible to define a file system rule using the system call rule syntax. The

following command creates a rule for system calls that is analogous to the -w

/etc/shadow -p wa file system rule:

~]# auditctl -a always,exit -F path=/etc/shadow -F perm=wa

5.5.2. Defining Executable File Rules

To define an executable file rule, use the following syntax:

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auditctl -a action,filter [ -F arch=cpu -S system_call] -F

exe=path_to_executable_file -k key_name

where:

action and filter specify when a certain event is logged. action can be either always or

never. filter specifies which kernel rule-matching filter is applied to the event. The rule-

matching filter can be one of the following: task, exit, user, and exclude. For more

information about these filters, see the beginning of Section 5.1, “Audit System

Architecture”.

system_call specifies the system call by its name. A list of all system calls can be

found in the /usr/include/asm/unistd_64.h file. Several system calls can be

grouped into one rule, each specified after its own -S option.

path_to_executable_file is the absolute path to the executable file that is audited.

key_name is an optional string that helps you identify which rule or a set of rules

generated a particular log entry.

Example 5.3. Execut able File Rules

To define a rule that logs all execution of the /bin/id program, execute the following

command:

~]# auditctl -F exe=/bin/id -S execve -k execution_bin_id

5.5.3. Defining Persist ent Audit Rules and Controls in the

/etc/audit/audit.rules File

To define Audit rules that are persistent across reboots, you must include them in the

/etc/audit/audit.rules file. This file uses the same auditctl command line syntax to

specify the rules. Empty lines and text following a hash sign (#) are ignored.

The auditctl command can also be used to read rules from a specified file using the -R

option, for example:

~]# auditctl -R /usr/share/doc/audit/rules/30-stig.rules

Defining Control Rules

A file can contain only the following control rules that modify the behavior of the Audit

system: -b, -D, -e, -f, -r, and --loginuid-immutable. For more information on these

options, see Section 5.5.1, “Defining Control Rules”.

Example 5.4. Cont rol Rules in audit.rules

# Delete all previous rules

-D

# Set buffer size

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-b 8192

# Make the configuration immutable -- reboot is required to change

audit rules

-e 2

# Panic when a failure occurs

-f 2

# Generate at most 100 audit messages per second

-r 100

# Make login UID immutable once it is set (may break containers)

--loginuid-immutable 1

Defining File Syst em and Syst em Call Rules

File system and system call rules are defined using the auditctl syntax. The examples

in Section 5.5.1, “Defining Audit Rules with audit ct l” can be represented with the following

rules file:

Example 5.5. File Syst em and Syst em Call Rules in audit.rules

-w /etc/passwd -p wa -k passwd_changes

-w /etc/selinux/ -p wa -k selinux_changes

-w /sbin/insmod -p x -k module_insertion

-a always,exit -F arch=b64 -S adjtimex -S settimeofday -k time_change

-a always,exit -S unlink -S unlinkat -S rename -S renameat -F

auid>=1000 -F auid!=4294967295 -k delete

Preconfigured Rules Files

In the /usr/share/doc/audit/rules/ directory, the audit package provides a set of pre-

configured rules files according to various certification standards:

30-nispom.rules — Audit rule configuration that meets the requirements specified in

the Information System Security chapter of the National Industrial Security Program

Operating Manual.

30-pci-dss-v31.rules — Audit rule configuration that meets the requirements set by

Payment Card Industry Data Security Standard (PCI DSS) v3.1.

30-stig.rules — Audit rule configuration that meets the requirements set by

Security Technical Implementation Guides (STIG).

To use these configuration files, create a backup of your original

/etc/audit/audit.rules file and copy the configuration file of your choice over the

/etc/audit/audit.rules file:

~]# cp /etc/audit/audit.rules /etc/audit/audit.rules_backup

~]# cp /usr/share/doc/audit/rules/30-stig.rules /etc/audit/audit.rules

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Note

The Audit rules have a numbering scheme that allows them to be ordered. To learn

more about the naming scheme, see the /usr/share/doc/audit/rules/README-

rules file.

5.6. Understanding Audit Log Files

By default, the Audit system stores log entries in the /var/log/audit/audit.log file; if

log rotation is enabled, rotated audit.log files are stored in the same directory.

The following Audit rule logs every attempt to read or modify the /etc/ssh/sshd_config

file:

-w /etc/ssh/sshd_config -p warx -k sshd_config

If the auditd daemon is running, for example, using the following command creates a new

event in the Audit log file:

~]$ cat /etc/ssh/sshd_config

This event in the audit.log file looks as follows:

type=SYSCALL msg=audit(1364481363.243:24287): arch=c000003e syscall=2

success=no exit=-13 a0=7fffd19c5592 a1=0 a2=7fffd19c4b50 a3=a items=1

ppid=2686 pid=3538 auid=1000 uid=1000 gid=1000 euid=1000 suid=1000

fsuid=1000 egid=1000 sgid=1000 fsgid=1000 tty=pts0 ses=1 comm="cat"

exe="/bin/cat" subj=unconfined_u:unconfined_r:unconfined_t:s0-

s0:c0.c1023 key="sshd_config"

type=CWD msg=audit(1364481363.243:24287): cwd="/home/shadowman"

type=PATH msg=audit(1364481363.243:24287): item=0

name="/etc/ssh/sshd_config" inode=409248 dev=fd:00 mode=0100600 ouid=0

ogid=0 rdev=00:00 obj=system_u:object_r:etc_t:s0

The above event consists of three records, which share the same time stamp and serial

number. Records always tart with the type= keyword. Each record consists of several

name=value pairs separated by a white space or a comma. A detailed analysis of the

above event follows:

First Record

type=SYSCALL

The type field contains the type of the record. In this example, the SYSCALL value

specifies that this record was triggered by a system call to the kernel.

For a list of all possible type values and their explanations, see Section B.2,

“Audit Record Types”.

msg=audit(1364481363.243:24287):

The msg field records:

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a time stamp and a unique ID of the record in the form

audit(time_stamp:ID). Multiple records can share the same time stamp and

ID if they were generated as part of the same Audit event. The time stamp is

using the Unix time format - seconds since 00:00:00 UTC on 1 January 1970.

various event-specific name=value pairs provided by the kernel or user space

applications.

arch=c000003e

The arch field contains information about the CPU architecture of the system. The

value, c000003e, is encoded in hexadecimal notation. When searching Audit

records with the ausearch command, use the -i or --interpret option to

automatically convert hexadecimal values into their human-readable equivalents.

The c000003e value is interpreted as x86_64.

syscall=2

The syscall field records the type of the system call that was sent to the kernel.

The value, 2, can be matched with its human-readable equivalent in the

/usr/include/asm/unistd_64.h file. In this case, 2 is the open system call. Note

that the ausyscall utility allows you to convert system call numbers to their

human-readable equivalents. Use the ausyscall --dump command to display a

listing of all system calls along with their numbers. For more information, see the

ausyscall(8) man page.

success=no

The success field records whether the system call recorded in that particular

event succeeded or failed. In this case, the call did not succeed.

exit=-13

The exit field contains a value that specifies the exit code returned by the

system call. This value varies for different system call. You can interpret the

value to its human-readable equivalent with the following command:

~]# ausearch --interpret --exit -13

Note that the previous example assumes that your Audit log contains an event

that failed with exit code -13.

a0=7fffd19c5592, a1=0, a2=7fffd19c5592, a3=a

The a0 to a3 fields record the first four arguments, encoded in hexadecimal

notation, of the system call in this event. These arguments depend on the

system call that is used; they can be interpreted by the ausearch utility.

items=1

The items field contains the number of auxiliary records that follow the syscall

record.

ppid=2686

The ppid field records the Parent Process ID (PPID). In this case, 2686 was the

PPID of the parent process such as bash.

pid=3538

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The pid field records the Process ID (PID). In this case, 3538 was the PID of the

cat process.

auid=1000

The auid field records the Audit user ID, that is the loginuid. This ID is assigned

to a user upon login and is inherited by every process even when the user's

identity changes, for example, by switching user accounts with the su - john

command.

uid=1000

The uid field records the user ID of the user who started the analyzed process.

The user ID can be interpreted into user names with the following command:

ausearch -i --uid UID.

gid=1000

The gid field records the group ID of the user who started the analyzed process.

euid=1000

The euid field records the effective user ID of the user who started the analyzed

process.

suid=1000

The suid field records the set user ID of the user who started the analyzed

process.

fsuid=1000

The fsuid field records the file system user ID of the user who started the

analyzed process.

egid=1000

The egid field records the effective group ID of the user who started the

analyzed process.

sgid=1000

The sgid field records the set group ID of the user who started the analyzed

process.

fsgid=1000

The fsgid field records the file system group ID of the user who started the

analyzed process.

tty=pts0

The tty field records the terminal from which the analyzed process was invoked.

ses=1

The ses field records the session ID of the session from which the analyzed

process was invoked.

comm="cat"

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The comm field records the command-line name of the command that was used to

invoke the analyzed process. In this case, the cat command was used to trigger

this Audit event.

exe="/bin/cat"

The exe field records the path to the executable that was used to invoke the

analyzed process.

subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

The subj field records the SELinux context with which the analyzed process was

labeled at the time of execution.

key="sshd_config"

The key field records the administrator-defined string associated with the rule

that generated this event in the Audit log.

Second Record

type=CWD

In the second record, the type field value is CWD — current working directory. This

type is used to record the working directory from which the process that invoked

the system call specified in the first record was executed.

The purpose of this record is to record the current process's location in case a

relative path winds up being captured in the associated PATH record. This way the

absolute path can be reconstructed.

msg=audit(1364481363.243:24287)

The msg field holds the same time stamp and ID value as the value in the first

record. The time stamp is using the Unix time format - seconds since 00:00:00

UTC on 1 January 1970.

cwd="/home/user_name"

The cwd field contains the path to the directory in which the system call was

invoked.

T hird Record

type=PATH

In the third record, the type field value is PATH. An Audit event contains a PATH-

type record for every path that is passed to the system call as an argument. In

this Audit event, only one path (/etc/ssh/sshd_config) was used as an

argument.

msg=audit(1364481363.243:24287):

The msg field holds the same time stamp and ID value as the value in the first

and second record.

item=0

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The item field indicates which item, of the total number of items referenced in

the SYSCALL type record, the current record is. This number is zero-based; a

value of 0 means it is the first item.

name="/etc/ssh/sshd_config"

The name field records the full path of the file or directory that was passed to the

system call as an argument. In this case, it was the /etc/ssh/sshd_config file.

inode=409248

The inode field contains the inode number associated with the file or directory

recorded in this event. The following command displays the file or directory that

is associated with the 409248 inode number:

~]# find / -inum 409248 -print

/etc/ssh/sshd_config

dev=fd:00

The dev field specifies the minor and major ID of the device that contains the file

or directory recorded in this event. In this case, the value represents the

/dev/fd/0 device.

mode=0100600

The mode field records the file or directory permissions, encoded in numerical

notation as returned by the stat command in the st_mode field. See the stat(2)

man page for more information. In this case, 0100600 can be interpreted as -rw-

------, meaning that only the root user has read and write permissions to the

/etc/ssh/sshd_config file.

ouid=0

The ouid field records the object owner's user ID.

ogid=0

The ogid field records the object owner's group ID.

rdev=00:00

The rdev field contains a recorded device identifier for special files only. In this

case, it is not used as the recorded file is a regular file.

obj=system_u:object_r:etc_t:s0

The obj field records the SELinux context with which the recorded file or directory

was labeled at the time of execution.

The Audit event analyzed above contains only a subset of all possible fields that an event

can contain. For a list of all event fields and their explanation, see Section B.1, “Audit

Event Fields”. For a list of all event types and their explanation, see Section B.2, “Audit

Record Types”.

Example 5.6. Addit io nal audit.log Event s

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The following Audit event records a successful start of the auditd daemon. The ver

field shows the version of the Audit daemon that was started.

type=DAEMON_START msg=audit(1363713609.192:5426): auditd start,

ver=2.2 format=raw kernel=2.6.32-358.2.1.el6.x86_64 auid=1000 pid=4979

subj=unconfined_u:system_r:auditd_t:s0 res=success

The following Audit event records a failed attempt of user with UID of 1000 to log in as

the root user.

type=USER_AUTH msg=audit(1364475353.159:24270): user pid=3280 uid=1000

auid=1000 ses=1 subj=unconfined_u:unconfined_r:unconfined_t:s0-

s0:c0.c1023 msg='op=PAM:authentication acct="root" exe="/bin/su"

hostname=? addr=? terminal=pts/0 res=failed'

5.7. Searching the Audit Log Files

The ausearch utility allows you to search Audit log files for specific events. By default,

ausearch searches the /var/log/audit/audit.log file. You can specify a different file

using the ausearch options -if file_name command. Supplying multiple options in one

ausearch command is equivalent to using the AND operator between field types and the

OR operator between multiple instances of the same field type.

Example 5.7. Using ausearch to Search Audit Log Files

To search the /var/log/audit/audit.log file for failed login attempts, use the

following command:

~]# ausearch --message USER_LOGIN --success no --interpret

To search for all account, group, and role changes, use the following command:

~]# ausearch -m ADD_USER -m DEL_USER -m ADD_GROUP -m USER_CHAUTHTOK -m

DEL_GROUP -m CHGRP_ID -m ROLE_ASSIGN -m ROLE_REMOVE -i

To search for all logged actions performed by a certain user, using the user's login ID

(auid), use the following command:

~]# ausearch -ua 1000 -i

To search for all failed system calls from yesterday up until now, use the following

command:

~]# ausearch --start yesterday --end now -m SYSCALL -sv no -i

For a full listing of all ausearch options, see the ausearch(8) man page.

5.8. Creating Audit Reports

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The aurepo rt utility allows you to generate summary and columnar reports on the

events recorded in Audit log files. By default, all audit.log files in the /var/log/audit/

directory are queried to create the report. You can specify a different file to run the report

against using the aureport options -if file_name command.

Example 5.8. Using aureport to Generat e Audit Report s

To generate a report for logged events in the past three days excluding the current

example day, use the following command:

~]# aureport --start 04/08/2013 00:00:00 --end 04/11/2013 00:00:00

To generate a report of all executable file events, use the following command:

~]# aureport -x

To generate a summary of the executable file event report above, use the following

command:

~]# aureport -x --summary

To generate a summary report of failed events for all users, use the following

command:

~]# aureport -u --failed --summary -i

To generate a summary report of all failed login attempts per each system user, use

the following command:

~]# aureport --login --summary -i

To generate a report from an ausearch query that searches all file access events for

user ID 1000, use the following command:

~]# ausearch --start today --loginuid 1000 --raw | aureport -f --

summary

To generate a report of all Audit files that are queried and the time range of events

they include, use the following command:

~]# aureport -t

For a full listing of all aureport options, see the aureport(8) man page.

5.9. Additional Resources

For more information about the Audit system, see the following sources.

Online Sources

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The Linux Audit Documentation Project page: https://github.com/linux-audit/audit-

documentation/wiki.

Installed Document ation

Documentation provided by the audit package can be found in the

/usr/share/doc/audit/ directory.

Manual Pages

audispd.conf(5)

auditd.conf(5)

ausearch-expression(5)

audit.rules(7)

audispd(8)

auditctl(8)

auditd(8)

aulast(8)

aulastlog(8)

aureport(8)

ausearch(8)

ausyscall(8)

autrace(8)

auvirt(8)

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Chapter 6. Compliance and Vulnerability Scanning with

OpenSCAP

6.1. Security Compliance in Red Hat Enterprise Linux

A compliance audit is a process of figuring out whether a given object follows all the rules

written out in a compliance policy. The compliance policy is defined by security

professionals who specify desired settings, often in the form of a checklist, that are to be

used in the computing environment.

The compliance policy can vary substantially across organizations and even across

different systems within the same organization. Differences among these policies are

based on the purpose of these systems and its importance for the organization. The

custom software settings and deployment characteristics also raise a need for custom

policy checklists.

Red Hat Enterprise Linux provides tools that allow for fully automated compliance audit.

These tools are based on the Security Content Automation Protocol (SCAP) standard and

are designed for automated tailoring of compliance policies.

Securit y Compliance Too ls Support ed on Red Hat Ent erprise Linux 7

SCAP Wo rkbench — The scap-workbench graphical utility is designed to perform

configuration and vulnerability scans on a single local or remote system. It can be also

used to generate security reports based on these scans and evaluations.

OpenSCAP — The o scap command-line utility is designed to perform configuration and

vulnerability scans on a local system, to validate security compliance content, and to

generate reports and guides based on these scans and evaluations.

Script Check Engine (SCE) — SCE is an extension to the SCAP protocol that allows

administrators to write their security content using a scripting language, such as Bash,

Python, or Ruby. The SCE extension is provided in the openscap-engine-sce package.

SCAP Securit y Guide (SSG) — The scap-security-guide package provides the latest

collection of security policies for Linux systems. The guidance consists of a catalog of

practical hardening advice, linked to government requirements where applicable. The

project bridges the gap between generalized policy requirements and specific

implementation guidelines.

If you require performing automated compliance audits on multiple systems remotely, you

can utilize OpenSCAP solution for Red Hat Satellite. For more information see Section 6.7,

“Using OpenSCAP with Red Hat Satellite” and Section 6.9, “Additional Resources”.

6.2. Defining Compliance Policy

The security or compliance policy is rarely written from scratch. ISO 27000 standard

series, derivative works, and other sources provide security policy templates and practice

recommendations that should be helpful to start with. However, organizations building

theirs information security program need to amend the policy templates to align with their

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187

needs. The policy template should be chosen on the basis of its relevancy to the company

environment and then the template has to be adjusted because either the template

contains build-in assumptions which cannot be applied to the organization, or the template

explicitly requires that certain decisions have to be made.

Red Hat Enterprise Linux auditing capabilities are based on the Security Content

Automation Protocol (SCAP) standard. SCAP is a synthesis of interoperable specifications

that standardize the format and nomenclature by which software flaw and security

configuration information is communicated, both to machines and humans. SCAP is a multi-

purpose framework of specifications that supports automated configuration, vulnerability

and patch checking, technical control compliance activities, and security measurement.

In other words, SCAP is a vendor-neutral way of expressing security policy, and as such it

is widely used in modern enterprises. SCAP specifications create an ecosystem where

the format of security content is well known and standardized while the implementation of

the scanner or policy editor is not mandated. Such a status enables organizations to build

their security policy (SCAP content) once, no matter how many security vendors do they

employ.

The latest version of SCAP includes several underlying standards. These components are

organized into groups according to their function within SCAP as follows:

SCAP Co mponents

Languages — This group consists of SCAP languages that define standard vocabularies

and conventions for expressing compliance policy.

The eXtensible Configuration Checklist Description Format (XCCDF) — A language

designed to express, organize, and manage security guidance.

Open Vulnerability and Assessment Language (OVAL) — A language developed to

perform logical assertion about the state of the scanned system.

Open Checklist Interactive Language (OCIL) — A language designed to provide a

standard way to query users and interpret user responses to the given questions.

Asset Identification (AI) — A language developed to provide a data model, methods,

and guidance for identifying security assets.

Asset Reporting Format (ARF) — A language designed to express the transport

format of information about collected security assets and the relationship between

assets and security reports.

Enumerations — This group includes SCAP standards that define naming format and an

official list or dictionary of items from certain security-related areas of interest.

Common Configuration Enumeration (CCE) — An enumeration of security-relevant

configuration elements for applications and operating systems.

Common Platform Enumeration (CPE) — A structured naming scheme used to identify

information technology (IT) systems, platforms, and software packages.

Common Vulnerabilities and Exposures (CVE) — A reference method to a collection of

publicly known software vulnerabilities and exposures.

Metrics — This group comprises of frameworks to identify and evaluate security risks.

Common Configuration Scoring System (CCSS) — A metric system to evaluate

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security-relevant configuration elements and assign them scores in order to help

users to prioritize appropriate response steps.

Common Vulnerability Scoring System (CVSS) — A metric system to evaluate

software vulnerabilities and assign them scores in order to help users prioritize

their security risks.

Integrity — An SCAP specification to maintain integrity of SCAP content and scan results.

Trust Model for Security Automation Data (TMSAD) — A set of recommendations

explaining usage of existing specification to represent signatures, hashes, key

information, and identity information in context of an XML file within a security

automation domain.

Each of the SCAP components has its own XML-based document format and its XML name

space. A compliance policy expressed in SCAP can either take a form of a single OVAL

definition XML file, data stream file, single zip archive, or a set of separate XML files

containing an XCCDF file that represents a policy checklist.

6.2.1. T he XCCDF File Format

The XCCDF language is designed to support information interchange, document

generation, organizational and situational tailoring, automated compliance testing, and

compliance scoring. The language is mostly descriptive and does not contain any

commands to perform security scans. However, an XCCDF document can refer to other

SCAP components, and as such it can be used to craft a compliance policy that is portable

among all the target platforms with the exception of the related assessment documents

(OVAL, OCIL).

The common way to represent a compliance policy is a set of XML files where one of the

files is an XCCDF checklist. This XCCDF file usually points to the assessment resources,

multiple OVAL, OCIL and the Script Check Engine (SCE) files. Furthermore, the file set can

contain a CPE dictionary file and an OVAL file defining objects for this dictionary.

Being an XML-based language, the XCCDF defines and uses a vast selection of XML

elements and attributes. The following list briefly introduces the main XCCDF elements;

for more details about XCCDF, consult the NIST Interagency Report 7275 Revision 4.

Main XML Element s o f t he XCCDF Document

<xccdf:Benchmark> — This is a root element that encloses the whole XCCDF

document. It may also contain checklist metadata, such as a title, description, list of

authors, date of the latest modification, and status of the checklist acceptance.

<xccdf:Rule> — This is a key element that represents a checklist requirement and

holds its description. It may contain child elements that define actions verifying or

enforcing compliance with the given rule or modify the rule itself.

<xccdf:Value> — This key element is used for expressing properties of other XCCDF

elements within the benchmark.

<xccdf:Group> — This element is used to organize an XCCDF document to structures

with the same context or requirement domains by gathering the <xccdf:Rule>,

<xccdf:Value>, and <xccdf:Group> elements.

<xccdf:Profile> — This element serves for a named tailoring of the XCCDF

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benchmark. It allows the benchmark to hold several different tailorings.

<xccdf:Profile> utilizes several selector elements, such as <xccdf:select> or

<xccdf:refine-rule>, to determine which elements are going to be modified and

processed while it is in effect.

<xccdf:Tailoring> — This element allows defining the benchmark profiles outside the

benchmark, which is sometimes desirable for manual tailoring of the compliance policy.

<xccdf:TestResult> — This element serves for keeping the scan results for the

given benchmark on the target system. Each <xccdf:TestResult> should refer to the

profile that was used to define the compliance policy for the particular scan and it

should also contain important information about the target system that is relevant for

the scan.

<xccdf:rule-result> — This is a child element of <xccdf:TestResult> that is used

to hold the result of applying a specific rule from the benchmark to the target system.

<xccdf:fix> — This is a child element of <xccdf:Rule> that serves for remediation of

the target system that is not compliant with the given rule. It can contain a command or

script that is run on the target system in order to bring the system into compliance the

rule.

<xccdf:check> — This is a child element of <xccdf:Rule> that refers to an external

source which defines how to evaluate the given rule.

<xccdf:select> — This is a selector element that is used for including or excluding

the chosen rules or groups of rules from the policy.

<xccdf:set-value> — This is a selector element that is used for overwriting the

current value of the specified <xccdf:Value> element without modifying any of its

other properties.

<xccdf:refine-value> — This is a selector element that is used for specifying

constraints of the particular <xccdf:Value> element during policy tailoring.

<xccdf:refine-rule> — This selector element allows overwriting properties of the

selected rules.

Example 6.1. An Example o f an XCCDF Document

<?xml version="1.0" encoding="UTF-8"?>

<Benchmark xmlns="http://checklists.nist.gov/xccdf/1.2"

id="xccdf_com.example.www_benchmark_test">

<status>incomplete</status>

<title>Profile title is compulsory</title>

<select idref="xccdf_com.example.www_group_1"

selected="true"/>

<select idref="xccdf_com.example.www_rule_1"

selected="true"/>

<refine-value idref="xccdf_com.example.www_value_1"

selector="telnet service"/>

</Profile>

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<value selector="telnet_service">telnet-server</value>

<value selector="dhcp_servide">dhcpd</value>

<value selector="ftp_service">tftpd</value>

</Value>

<title>The telnet-server Package Shall Not Be Installed </title>

Removing the telnet-server package decreases the risk

of the telnet service’s accidental (or intentional) activation

</rationale>

<fix platform="cpe:/o:redhat:enterprise_linux:6"

reboot="false"

disruption="low"

system="urn:xccdf:fix:script:sh">

yum -y remove

</fix>

<check system="http://oval.mitre.org/XMLSchema/oval-definitions-

5">

<check-export value-id="xccdf_com.example.www_value_1"

export-name="oval:com.example.www:var:1"/>

<check-content-ref href="examplary.oval.xml"

name="oval:com.example.www:def:1"/>

</check>

<check-import import-name="stdout"/>

<check-content-ref href="telnet_server.sh"/>

</check>

</Rule>

</Group>

</Benchmark>

6.2.2. T he OVAL File Format

The Open Vulnerability Assessment Language (OVAL) is the essential and oldest

component of SCAP. The main goal of the OVAL standard is to enable interoperability

among security products. That is achieved by standardization of the following three

domains:

1. Representation of the target system configuration.

2. Analysis of the target system for the presence of a particular machine state.

3. Reporting the results of the comparison between the specified machine state and

the observed machine state.

Unlike other tools or custom scripts, the OVAL language describes a desired state of

resources in a declarative manner. The OVAL language code is never executed directly,

but by means of an OVAL interpreter tool called scanner. The declarative nature of OVAL

ensures that the state of the assessed system is not accidentally modified, which is

important because security scanners are often run with the highest possible privileges.

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OVAL specification is open for public comments and contribution and various IT companies

collaborate with the MITRE Corporation, federally funded not-for-profit organization. The

OVAL specification is continuously evolving and different editions are distinguished by a

version number. The current version 5.11.1 was released in April 2015.

Like all other SCAP components, OVAL is based on XML. The OVAL standard defines

several document formats. Each of them includes different kind of information and serves

a different purpose.

The OVAL Document Format s

The OVAL Definitions format is the most common OVAL file format that is used directly

for system scans. The OVAL Definitions document describes the desired state of the

target system.

The OVAL Variables format defines variables used to amend the OVAL Definitions

document. The OVAL Variables document is typically used in conjunction with the OVAL

Definitions document to tailor the security content for the target system at runtime.

The OVAL System Characteristics format holds information about the assessed system.

The OVAL System Characteristics document is typically used to compare the actual

state of the system against the expected state defined by an OVAL Definitions

document.

The OVAL Results is the most comprehensive OVAL format that is used to report

results of the system evaluation. The OVAL Results document typically contains copy of

the evaluated OVAL definitions, bound OVAL variables, OVAL system characteristics,

and results of tests that are computed based on comparison of the system

characteristics and the definitions.

The OVAL Directives format is used to tailor verbosity of an OVAL Result document by

either including or excluding certain details.

The OVAL Common Model format contains definitions of constructs and enumerations

used in several other OVAL schemes. It is used to reuse OVAL definitions in order to

avoid duplications across multiple documents.

The OVAL Definitions document consists of a set of configuration requirements where

each requirement is defined in the following five basic sections: definitions, tests, objects,

states, and variables. The elements within the definitions section describe which of the

tests shall be fulfilled to satisfy the given definition. The test elements link objects and

states together. During the system evaluation, a test is considered passed when a

resource of the assessed system that is denoted by the given object element

corresponds with the given state element. The variables section defines external

variables which may be used to adjust elements from the states section. Besides these

sections, the OVAL Definitions document typically contains also the generator and

signature sections. The generator section holds information about the document origin and

various additional information related to its content.

Each element from the OVAL document basic sections is unambiguously identified by an

identifier in the following form:

oval:namespace:type:ID

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where namespace is a name space defining the identifier, type is either def for definitions

elements, tst for tests elements, obj for objects element, ste for states elements, and var

for variables elements, and ID is an integer value of the identifier.

Example 6.2. An Example o f an OVAL Def init ions Do cument

<?xml version="1.0" encoding="utf-8"?>

<oval_definitions

xmlns:lin-def="http://oval.mitre.org/XMLSchema/oval-definitions-

5#linux"

xmlns:oval="http://oval.mitre.org/XMLSchema/oval-common-5"

xmlns="http://oval.mitre.org/XMLSchema/oval-definitions-5"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

<oval:product_name>vim</oval:product_name>

<oval:schema_version>5.10.1</oval:schema_version>

<oval:timestamp>2012-11-22T15:00:00+01:00</oval:timestamp>

</generator>

<definition class="inventory"

id="oval:org.open-scap.cpe.rhel:def:7"

version="1">

<title>Red Hat Enterprise Linux 7</title>

<platform>Red Hat Enterprise Linux 7</platform>

</affected>

<reference ref_id="cpe:/o:redhat:enterprise_linux:7"

source="CPE"/>

The operating system installed on the system is Red Hat

Enterprise Linux 7

</description>

</metadata>

<criterion comment="Red Hat Enterprise Linux 7 is installed"

test_ref="oval:org.open-scap.cpe.rhel:tst:7"/>

</criteria>

</definition>

</definitions>

<tests>

<lin-def:rpminfo_test check_existence="at_least_one_exists"

id="oval:org.open-scap.cpe.rhel:tst:7"

version="1"

check="at least one"

comment="redhat-release is version 7">

<lin-def:object object_ref="oval:org.open-scap.cpe.redhat-

release:obj:1"/>

<lin-def:state state_ref="oval:org.open-scap.cpe.rhel:ste:7"/>

</lin-def:rpminfo_test>

</tests>

<lin-def:rpmverifyfile_object id="oval:org.open-scap.cpe.redhat-

release:obj:1"

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version="1">

<!-- This object represents rpm package which owns /etc/redhat-

release file -->

<lin-def:behaviors nolinkto='true'

nomd5='true'

nosize='true'

nouser='true'

nogroup='true'

nomtime='true'

nomode='true'

nordev='true'

noconfigfiles='true'

noghostfiles='true' />

<lin-def:name operation="pattern match"/>

<lin-def:epoch operation="pattern match"/>

<lin-def:version operation="pattern match"/>

<lin-def:release operation="pattern match"/>

<lin-def:arch operation="pattern match"/>

<lin-def:filepath>/etc/redhat-release</lin-def:filepath>

</lin-def:rpmverifyfile_object>

</objects>

<lin-def:rpminfo_state id="oval:org.open-scap.cpe.rhel:ste:7"

version="1">

<lin-def:name operation="pattern match">^redhat-release</lin-

def:name>

<lin-def:version operation="pattern match">^7[^\d]</lin-

def:version>

</lin-def:rpminfo_state>

</states>

</oval_definitions>

6.2.3. T he Dat a St ream Format

SCAP data stream is a file format used since SCAP version 1.2 and it represents a bundle

of XCCDF, OVAL, and other component files which can be used to define a compliance

policy expressed by an XCCDF checklist. It also contains an index and catalog that allow

splitting the given data stream into files according to the SCAP components.

The data stream uses XML format that consists of a header formed by a table of contents

and a list of the <ds:component> elements. Each of these elements encompasses an

SCAP component such as XCCDF, OVAL, CPE, and other. The data stream file may contain

multiple components of the same type, and thus covering all security policies needed by

your organization.

Example 6.3. An Example o f a Dat a St ream Header

<ds:data-stream-collection

xmlns:ds="http://scap.nist.gov/schema/scap/source/1.2"

xmlns:xlink="http://www.w3.org/1999/xlink"

xmlns:cat="urn:oasis:names:tc:entity:xmlns:xml:catalog"

id="scap_org.open-scap_collection_from_xccdf_ssg-rhel7-xccdf-

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1.2.xml"

schematron-version="1.0">

<ds:data-stream id="scap_org.open-scap_datastream_from_xccdf_ssg-

rhel7-xccdf-1.2.xml"

scap-version="1.2" use-case="OTHER">

<ds:dictionaries>

<ds:component-ref id="scap_org.open-scap_cref_output--ssg-rhel7-

cpe-dictionary.xml"

xlink:href="#scap_org.open-scap_comp_output--ssg-rhel7-cpe-

dictionary.xml">

<cat:catalog>

<cat:uri name="ssg-rhel7-cpe-oval.xml"

uri="#scap_org.open-scap_cref_output--ssg-rhel7-cpe-

oval.xml"/>

</cat:catalog>

</ds:component-ref>

</ds:dictionaries>

<ds:checklists>

<ds:component-ref id="scap_org.open-scap_cref_ssg-rhel7-xccdf-

1.2.xml"

xlink:href="#scap_org.open-scap_comp_ssg-rhel7-xccdf-1.2.xml">

<cat:catalog>

<cat:uri name="ssg-rhel7-oval.xml"

uri="#scap_org.open-scap_cref_ssg-rhel7-oval.xml"/>

</cat:catalog>

</ds:component-ref>

</ds:checklists>

<ds:checks>

<ds:component-ref id="scap_org.open-scap_cref_ssg-rhel7-oval.xml"

xlink:href="#scap_org.open-scap_comp_ssg-rhel7-oval.xml"/>

<ds:component-ref id="scap_org.open-scap_cref_output--ssg-rhel7-

cpe-oval.xml"

xlink:href="#scap_org.open-scap_comp_output--ssg-rhel7-cpe-

oval.xml"/>

<ds:component-ref id="scap_org.open-scap_cref_output--ssg-rhel7-

oval.xml"

xlink:href="#scap_org.open-scap_comp_output--ssg-rhel7-

oval.xml"/>

</ds:checks>

</ds:data-stream>

<ds:component id="scap_org.open-scap_comp_ssg-rhel7-oval.xml"

timestamp="2014-03-14T16:21:59">

<oval_definitions xmlns="http://oval.mitre.org/XMLSchema/oval-

definitions-5"

xmlns:oval="http://oval.mitre.org/XMLSchema/oval-common-5"

xmlns:ind="http://oval.mitre.org/XMLSchema/oval-definitions-

5#independent"

xmlns:unix="http://oval.mitre.org/XMLSchema/oval-definitions-

5#unix"

xmlns:linux="http://oval.mitre.org/XMLSchema/oval-definitions-

5#linux"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://oval.mitre.org/XMLSchema/oval-common-

oval-common-schema.xsd

http://oval.mitre.org/XMLSchema/oval-definitions-5

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oval-definitions-schema.xsd

http://oval.mitre.org/XMLSchema/oval-definitions-

5#independent

independent-definitions-schema.xsd

http://oval.mitre.org/XMLSchema/oval-definitions-5#unix

unix-definitions-schema.xsd

http://oval.mitre.org/XMLSchema/oval-definitions-5#linux

linux-definitions-schema.xsd">

6.3. Using SCAP Workbench

SCAP Wo rkbench (scap-workbench) is a graphical utility that allows users to perform

configuration and vulnerability scans on a single local or a remote system, perform

remediation of the system, and generate reports based on scan evaluations. Note that

compared with the oscap command-line utility, SCAP Wo rkbench has only limited

functionality. SCAP Wo rkbench can also process only security content in the form of

XCCDF and data-stream files.

The following sections explain how to install, start, and utilize SCAP Workbench in order to

perform system scans, remediation, scan customization, and display relevant examples

for these tasks.

6.3.1. Inst alling SCAP Workbench

To install SCAP Wo rkbench on your system, enter the following command as root:

~]# yum install scap-workbench

This command installs all packages required by SCAP Workbench to function properly,

including the scap-workbench package that provides the utility itself. Note that required

dependencies, such as the qt and openssh packages, will be automatically updated to the

newest available version if the packages are already installed on your system.

Before you can start using SCAP Workbench effectively, you also need to install or import

some security content on your system. For example, you can install the SCAP Security

Guide (SSG) package, scap-security-guide, which contains the currently most evolved and

elaborate set of security polices for Linux systems. To install the SCAP Security Guide

package on your system, enter the following command as root:

~]# yum install scap-security-guide

After you install scap-security-guide on your system, unless specified otherwise, the SSG

security content is available under the /usr/share/xml/scap/ssg/content/ directory,

and you can proceed with other security compliance operations.

To find other possible sources of existing SCAP content that might suit your needs, see

Section 6.9, “Additional Resources”.

6.3.2. Running SCAP Workbench

After a successful installation of both, the SCAP Wo rkbench utility and SCAP content, you

can start using SCAP Wo rkbench on your systems. For running SCAP Wo rkbench from

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the GNOME Classic desktop environment, press the Super key to enter the Activities

Overview, type scap-workbench, and then press Enter. The Super key appears in a

variety of guises, depending on the keyboard and other hardware, but often as either the

Windows or Command key, and typically to the left of the Spacebar key.

Figure 6.1. Open SCAP Securit y Guide Window

As soon as you start the utility, the Open SCAP Security Guide window appears. After a

selection one of the guides, the SCAP Workbench window appears. This window consists of

several interactive components, which you should become familiar with before you start

scanning your system:

File

This menu list offers several options to load or save a SCAP-related content. To

show the initial Open SCAP Security Guide window, click the menu item with the

same name. Alternatively, load another customization file in the XCCDF format by

clicking Open Other Content. To save your customization as an XCCDF XML file,

use the Save Customization Only item. The Save All allows you to save SCAP

files either to the selected directory or as an RPM package.

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Cust omizat ion

This combo box informs you about the customization used for the given security

policy. You can select custom rules that will be applied for the system evaluation

by clicking this combo box. The default value is (no cust omizat ion), which

means that there will be no changes to the used security policy. If you made any

changes to the selected security profile, you can save those changes as an XML

file by clicking the Save Customization Only item in the File menu.

Pro f ile

This combo box contains the name of the selected security profile. You can select

the security profile from a given XCCDF or data-stream file by clicking this combo

box. To create a new profile that inherits properties of the selected security

profile, click the Customize button.

Target

The two radio buttons enable you to select whether the system to be evaluated

is a local or remote machine.

Select ed Rules

This field displays a list of security rules that are subject of the security policy.

Expanding a particular security rule provides detailed information about that rule.

St at us bar

This is a graphical bar that indicates status of an operation that is being

performed.

Fet ch remot e reso urces

This check box allows to instruct the scanner to download a remote OVAL content

defined in an XML file.

Dry run

Use this check box to get command line arguments to the diagnostics window

instead of running the scan.

Remediat e

This check box enables the remediation feature during the system evaluation. If

you check this box, SCAP Workbench will attempt to correct system settings that

would fail to match the state defined by the policy.

Scan

This button allows you to start the evaluation of the specified system.

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Figure 6.2. SCAP Workbench Window

6.3.3. Scanning the System

The main functionality of SCAP Workbench is to perform security scans on a selected

system in accordance with the given XCCDF or data stream file. To evaluate your system

against the selected security policy, follow these steps:

1. Select a security policy by using either the Open SCAP Security Guide window, or

Open Other Content in the File menu and search the respective XCCDF, SCAP

RPM or data stream file.

Warning

Selecting a security policy results in the loss of any previous customization

changes that were not saved. To re-apply the lost options, you have to

choose the available profile and customization content again. Note that your

previous customizations may not be applicable with the new security policy.

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2. To use a pre-arranged a file with customized security content specific to your use

case, you can load this file by clicking on the Cust omizat io n combo box. You can

also create a custom tailoring file by altering an available security profile. For more

information, see Section 6.3.4, “Customizing Security Profiles”.

a. Select the (no customization) option if you do not want to use any

customization for the current system evaluation. This is the default option if

no previous customization was selected.

b. Select the (open customization file...) option to search for the

particular tailoring file to be used for the current system evaluation.

c. If you have previously used some customization file, SCAP Wo rkbench

remembers this file and adds it to the list. This simplifies repetitive

application of the same scan.

3. Select a suitable security profile by clicking the Prof ile combo box.

a. To modify the selected profile, click the Customize button. For more

information about profile customization, see Section 6.3.4, “Customizing

Security Profiles”.

4. Select either of two Target radio buttons to scan either a local or a remote

machine.

a. If you have selected a remote system, specify it by entering the user name,

host name, and the port information as shown in the following example. If

you have previously used the remote scan, you can also select a remote

system from a list of recently scanned machines.

Figure 6.3. Specif ying a Remot e Syst em

5. You can allow automatic correction of the system configuration by selecting the

Remediate check box. With this option enabled, SCAP Wo rkbench attempts to

change the system configuration in accordance with the security rules applied by

the policy, should the related checks fail during the system scan.

Warning

If not used carefully, running the system evaluation with the remediation

option enabled could render the system non-functional.

6. Click the Scan button to initiate the system scan.

6.3.4. Customizing Security Profiles

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After selecting the security profile that suits your security policy, you can further adjust it

by clicking the Customize button. This will open the new Customization window that allows

you to modify the currently selected XCCDF profile without actually changing the

respective XCCDF file.

Figure 6.4. Cust omizing t he Select ed Securit y Prof ile

The Customization window contains a complete set of XCCDF elements relevant to the

selected security profile with detailed information about each element and its functionality.

You can enable or disable these elements by selecting or de-selecting the respective

check boxes in the main field of this window. The Customization window also supports

undo and redo functionality; you can undo or redo your selections by clicking the

respective arrow icon in the top left corner of the window.

You can also change variables that will later be used for evaluation. Find the desired item

in the Customization window, navigate to the right part and use the Modify value field.

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Figure 6.5. Set t ing a value f o r t he select ed it em in t he Cust o mizat ion windo w

After you have finished your profile customizations, confirm the changes by clicking the

Confirm Customization button. Your changes are now in the memory and do not persist

if SCAP Wo rkbench is closed or certain changes, such as selecting a new SCAP content

or choosing another customization option, are made. To store your changes, click the Save

Customization button in the SCAP Workbench window. This action allows you to save your

changes to the security profile as an XCCDF customization file in the chosen directory.

Note that this customization file can be further selected with other profiles.

6.3.5. Saving SCAP Cont ent

SCAP Wo rkbench also allows you to save SCAP content that is used with your system

evaluations. You can either save a customization file separately (see Section 6.3.4,

“Customizing Security Profiles”) or you can save all security content at once by clicking the

Save content combo box and selecting either the Save into a directory or Save as

RPM options.

By selecting the Save into a directory option, SCAP Workbench saves both the

XCCDF or data-stream file and the customization file to the specified location. This can be

useful as a backup solution.

By selecting the Save as RPM option, you can instruct SCAP Wo rkbench to create an

RPM package containing the XCCDF or data stream file and customization file. This is

useful for distributing the desired security content to systems that cannot be scanned

remotely, or just for delivering the content for further processing.

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Figure 6.6. Saving t he Current SCAP Cont ent as an RPM Package

6.3.6. Viewing Scan Results and Generat ing Scan Reports

After the system scan is finished, three new buttons, Clear, Save Results, and Show

Report, will appear instead of the Scan button.

Warning

Clicking the Clear button permanently removes the scan results.

To store the scan results in the form of an XCCDF, ARF, or HTML file, click the Save

Results combo box. Choose the HTML Report option to generate the scan report in

human-readable form. The XCCDF and ARF (data stream) formats are suitable for further

automatic processing. You can repeatedly choose all three options.

If you prefer to view the scan results immediately without saving them, you can click the

Show Report button, which opens the scan results in the form of a temporary HTML file in

your default web browser.

6.4. Using oscap

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The oscap command-line utility allows users to scan their local systems, validate security

compliance content, and generate reports and guides based on these scans and

evaluations. This utility serves as a front end to the OpenSCAP library and groups its

functionalities to modules (sub-commands) based on the type of SCAP content it

processes.

The following sections explain how to install oscap and perform the most common

operations. Examples are provided to illustrate these tasks. To learn more about specific

sub-commands, use the --help option with an o scap command:

oscap [options] module module_operation

[module_operation_options_and_arguments] --help

where module represents the type of SCAP content that is being processed, and

module_operation is a sub-command for the specific operation on the SCAP content.

Example 6.4. Get t ing Help on a Specif ic oscap Operation

~]$ oscap ds sds-split --help

oscap -> ds -> sds-split

Split given SourceDataStream into separate files

Usage: oscap [options] ds sds-split [options] SDS TARGET_DIRECTORY

SDS - Source data stream that will be split into multiple files.

TARGET_DIRECTORY - Directory of the resulting files.

Options:

--datastream-id <id> - ID of the datastream in the

collection to use.

--xccdf-id <id> - ID of XCCDF in the datastream that

should be evaluated.

To learn about all o scap features and the complete list of its options, see the oscap(8)

manual page.

6.4.1. Inst alling oscap

To install o scap to your system, enter the following command as root:

~]# yum install openscap-scanner

This command allows you to install all packages required by oscap to function properly,

including the openscap package. To be able to write your own security content, you should

also install the openscap-engine-sce package, which provides the Script Check Engine

(SCE). The SCE is an extension of the SCAP protocol that allows content authors to write

their security content using a scripting language, such as Bash, Python, or Ruby. Note that

the openscap-engine-sce package is only available from the Optional channel. See Enabling

Supplementary and Optional Repositories.

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Optionally, after installing oscap, you can check the capabilities of your version of oscap,

what specifications it supports, where the certain oscap files are stored, what kinds of

SCAP objects you can use, and other useful information. To display this information, type

the following command:

~]$ oscap -V

OpenSCAP command line tool (oscap) 1.0.4

==== Supported specifications ====

XCCDF Version: 1.2

OVAL Version: 5.10.1

CPE Version: 2.3

CVSS Version: 2.0

CVE Version: 2.0

Asset Identification Version: 1.1

Asset Reporting Format Version: 1.1

==== Capabilities added by auto-loaded plugins ====

SCE Version: 1.0 (from libopenscap_sce.so.8)

==== Paths ====

Schema files: /usr/share/openscap/schemas

Schematron files: /usr/share/openscap/xsl

Default CPE files: /usr/share/openscap/cpe

Probes: /usr/libexec/openscap

==== Inbuilt CPE names ====

Red Hat Enterprise Linux - cpe:/o:redhat:enterprise_linux

Red Hat Enterprise Linux 5 - cpe:/o:redhat:enterprise_linux:5

Red Hat Enterprise Linux 6 - cpe:/o:redhat:enterprise_linux:6

Red Hat Enterprise Linux 7 - cpe:/o:redhat:enterprise_linux:7

Fedora 16 - cpe:/o:fedoraproject:fedora:16

Fedora 17 - cpe:/o:fedoraproject:fedora:17

Fedora 18 - cpe:/o:fedoraproject:fedora:18

Fedora 19 - cpe:/o:fedoraproject:fedora:19

Fedora 20 - cpe:/o:fedoraproject:fedora:20

Fedora 21 - cpe:/o:fedoraproject:fedora:21

Red Hat Enterprise Linux Optional Productivity Applications -

cpe:/a:redhat:rhel_productivity

Red Hat Enterprise Linux Optional Productivity Applications 5 -

cpe:/a:redhat:rhel_productivity:5

==== Supported OVAL objects and associated OpenSCAP probes ====

system_info probe_system_info

family probe_family

filehash probe_filehash

environmentvariable probe_environmentvariable

textfilecontent54 probe_textfilecontent54

textfilecontent probe_textfilecontent

variable probe_variable

xmlfilecontent probe_xmlfilecontent

environmentvariable58 probe_environmentvariable58

filehash58 probe_filehash58

inetlisteningservers probe_inetlisteningservers

rpminfo probe_rpminfo

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partition probe_partition

iflisteners probe_iflisteners

rpmverify probe_rpmverify

rpmverifyfile probe_rpmverifyfile

rpmverifypackage probe_rpmverifypackage

selinuxboolean probe_selinuxboolean

selinuxsecuritycontext probe_selinuxsecuritycontext

file probe_file

interface probe_interface

password probe_password

process probe_process

runlevel probe_runlevel

shadow probe_shadow

uname probe_uname

xinetd probe_xinetd

sysctl probe_sysctl

process58 probe_process58

fileextendedattribute probe_fileextendedattribute

routingtable probe_routingtable

Before you can start using oscap effectively, you also need to install or import some

security content on your system. For example, you can install the SCAP Security Guide

(SSG) package, scap-security-guide, which contains the currently most evolved and

elaborate set of security polices for Linux systems. To install the SCAP Security Guide

package on your system, enter the following command as root:

~]# yum install scap-security-guide

After you install scap-security-guide on your system, unless specified otherwise, the SSG

security content is available under the /usr/share/xml/scap/ssg/content/ directory,

and you can proceed with other security compliance operations.

To find other possible sources of existing SCAP content that might suit your needs, see

Section 6.9, “Additional Resources”.

After installing the SCAP content on your system, o scap can process the content when

supplied with the file path to the content. The o scap utility supports SCAP version 1.2 and

is backward-compatible with SCAP versions 1.1 and 1.0, so it can process earlier versions

of SCAP content without any special requirements.

6.4.2. Displaying SCAP Cont ent

SCAP standard defines numerous file formats. The oscap utility can process or create

files conforming to many of the formats. In order to further process the given file with

SCAP content, you need to understand how to use o scap with the given file type. If you

are unsure how to use a particular file, you can either open and read the file, or you can

use the info module of oscap which parses the file and extracts relevant information in

human-readable format.

enter the following command to examine the internal structure of a SCAP document and

display useful information such as the document type, specification version, a status of

the document, the date the document was published, and the date the document was

copied to a file system:

oscap info file

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where file is the full path to the security content file being examined. The following

example better illustrates the usage of the oscap info command:

Example 6.5. Displaying Inf o rmat ion About SCAP Cont ent

~]$ oscap info /usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml

Document type: Source Data Stream

Imported: 2014-03-14T12:22:01

Stream: scap_org.open-scap_datastream_from_xccdf_ssg-rhel7-xccdf-

1.2.xml

Generated: (null)

Version: 1.2

Checklists:

Ref-Id: scap_org.open-scap_cref_ssg-rhel7-xccdf-1.2.xml

Profiles:

xccdf_org.ssgproject.content_profile_test

xccdf_org.ssgproject.content_profile_rht-ccp

xccdf_org.ssgproject.content_profile_common

xccdf_org.ssgproject.content_profile_stig-

rhel7-server-upstream

Referenced check files:

ssg-rhel7-oval.xml

system:

http://oval.mitre.org/XMLSchema/oval-definitions-5

Checks:

Ref-Id: scap_org.open-scap_cref_ssg-rhel7-oval.xml

Ref-Id: scap_org.open-scap_cref_output--ssg-rhel7-cpe-oval.xml

Ref-Id: scap_org.open-scap_cref_output--ssg-rhel7-oval.xml

Dictionaries:

Ref-Id: scap_org.open-scap_cref_output--ssg-rhel7-cpe-

dictionary.xml

6.4.3. Scanning t he System

The most important functionality of oscap is to perform configuration and vulnerability

scans of a local system. The following is a general syntax of the respective command:

oscap [options] module eval [module_operation_options_and_arguments]

The oscap utility can scan systems against the SCAP content represented by both an

XCCDF (The eXtensible Configuration Checklist Description Format) benchmark and OVAL

(Open Vulnerability and Assessment Language) definitions. The security policy can be in

the form of a single OVAL or XCCDF file or multiple separate XML files where each file

represents a different component (XCCDF, OVAL, CPE, CVE, and others). The result of a

scan can be printed to both standard output and an XML file. The result file can then be

further processed by oscap in order to generate a report in a human-readable format.

The following examples illustrate the most common usage of the command.

Example 6.6. Scanning t he Syst em Using t he SSG OVAL def init ions

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To scan your system against the SSG OVAL definition file while evaluating all definitions,

enter the following command:

~]$ oscap oval eval --results scan-oval-results.xml

/usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml

The results of the scan are stored as the scan-oval-results.xml file in the current

directory.

Example 6.7. Scanning t he Syst em Using t he SSG OVAL def init ions

To evaluate a particular OVAL definition from the security policy represented by the

SSG data stream file, enter the following command:

~]$ oscap oval eval --id oval:ssg:def:100 --results scan-oval-

results.xml /usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml

The results of the scan are stored as the scan-oval-results.xml file in the current

directory.

Example 6.8. Scanning t he Syst em Using t he SSG XCCDF benchmark

To perform the SSG XCCDF benchmark for the

xccdf_org.ssgproject.content_profile_rht-ccp profile on your system, enter the

following command:

~]$ oscap xccdf eval --profile

xccdf_org.ssgproject.content_profile_rht-ccp --results scan-xccdf-

results.xml /usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml

The results of the scan are stored as the scan-xccdf-results.xml file in the current

directory.

Note

The --profile command-line argument selects the security profile from the

given XCCDF or data stream file. The list of available profiles can be obtained by

running the oscap info command. If the --profile command-line argument is

omitted the default XCCDF profile is used as required by SCAP standard. Note that

the default XCCDF profile may or may not be an appropriate security policy.

6.4.4. Generating Report s and Guides

Another useful features of oscap is the ability to generate SCAP content in a human-

readable format. The oscap utility allows you to transform an XML file into the HTML or

plain-text format. This feature is used to generate security guides and checklists, which

serve as a source of information, as well as guidance for secure system configuration.

The results of system scans can also be transformed to well-readable result reports. The

general command syntax is the following:

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oscap module generate sub-module [specific_module/sub-

module_options_and_arguments] file

where module is either xccdf or oval, sub-module is a type of the generated document,

and file represents an XCCDF or OVAL file.

The following are the most common examples of the command usage:

Example 6.9. Generat ing a Guide wit h a Checklist

To produce an SSG guide with a checklist for the

xccdf_org.ssgproject.content_profile_rht-ccp profile, enter the following

command:

~]$ oscap xccdf generate guide --profile

xccdf_org.ssgproject.content_profile_rht-ccp

/usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml > ssg-guide-

checklist.html

The guide is stored as the ssg-guide-checklist.html file in the current directory.

Example 6.10. T ransf orming an SSG OVAL Scan Result int o a Report

To transform a result of an SSG OVAL scan into an HTML file, enter the following

command:

~]$ oscap oval generate report scan-oval-results.xml > ssg-scan-oval-

report.html

The result report is stored as the ssg-scan-oval-report.html file in the current

directory. This example assumes that you run the command from the same location

where the scan-oval-results.xml file is stored. Otherwise you need to specify the

fully-qualified path of the file that contains the scan results.

Example 6.11. Transf orming an SSG XCCDF Scan Result int o a Report

To transform a result of an SSG XCCDF scan into an HTML file, enter the following

command:

~]$ oscap xccdf generate report scan-xccdf-results.xml > scan-xccdf-

report.html

The result report is stored as the ssg-scan-xccdf-report.html file in the current

directory. Alternatively, you can generate this report in the time of the scan using the -

-report command-line argument:

~]$ oscap xccdf eval --profile

xccdf_org.ssgproject.content_profile_rht-ccp --results scan-xccdf-

results.xml --report scan-xccdf-report.html

/usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml

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6.4.5. Validating SCAP Content

Before you start using a security policy on your systems, you should first verify the policy

in order to avoid any possible syntax or semantic errors in the policy. The o scap utility

can be used to validate the security content against standard SCAP XML schemas. The

validation results are printed to the standard error stream (stderr). The general syntax of

such a validation command is the following:

oscap module validate [module_options_and_arguments] file

where file is the full path to the file being validated. The only exception is the data stream

module (ds), which uses the sds-validate operation instead of validate. Note that all

SCAP components within the given data stream are validated automatically and none of

the components is specified separately, as can be seen in the following example:

~]$ oscap ds sds-validate /usr/share/xml/scap/ssg/content/ssg-rhel7-

ds.xml

With certain SCAP content, such as OVAL specification, you can also perform a Schematron

validation. The Schematron validation is slower than the standard validation but provides

deeper analysis, and is thus able to detect more errors. The following SSG example

shows typical usage of the command:

~]$ oscap oval validate --schematron

/usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml

6.4.6. Using OpenSCAP t o Remediat e t he System

OpenSCAP allows to automatically remediate systems that have been found in a non-

compliant state. For system remediation, an XCCDF file with instructions is required. The

scap-security-guide package constains certain remediation instructions.

System remediation consists of the following steps:

1. OpenSCAP performs a regular XCCDF evaluation.

2. An assessment of the results is performed by evaluating the OVAL definitions.

Each rule that has failed is marked as a candidate for remediation.

3. OpenSCAP searches for an appropriate fix element, resolves it, prepares the

environment, and executes the fix script.

4. Any output of the fix script is captured by OpenSCAP and stored within the rule-

result element. The return value of the fix script is stored as well.

5. Whenever OpenSCAP executes a fix script, it immediatelly evaluates the OVAL

definition again (to verify that the fix script has been applied correctly). During this

second run, if the OVAL evaluation returns success, the result of the rule is fixed,

otherwise it is an error.

6. Detailed results of the remediation are stored in an output XCCDF file. It contains

two TestResult elements. The first TestResult element represents the scan

prior to the remediation. The second TestResult is derived from the first one and

contains remediation results.

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There are three modes of operation of OpenSCAP with regard to remediation: online,

offline, and review.

6.4.6.1. OpenSCAP Online Remediation

Online remediation executes fix elements at the time of scanning. Evaluation and

remediation are performed as a part of a single command.

To enable online remediation, use the --remediate command-line option. For example, to

execute online remediation using the scap-security-guide package, run:

~]$ oscap xccdf eval --remediate --profile

xccdf_org.ssgproject.content_profile_rht-ccp --results scan-xccdf-

results.xml /usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml

The output of this command consists of two sections. The first section shows the result of

the scan prior to the remediation, and the second section shows the result of the scan

after applying the remediation. The second part can contain only fixed and error results.

The fixed result indicates that the scan performed after the remediation passed. The

error result indicates that even after applying the remediation, the evaluation still does

not pass.

6.4.6.2. OpenSCAP Of f line Remediation

Offline remediation allows you to postpone fix execution. In the first step, the system is

only evaluated, and the results are stored in a TestResult element in an XCCDF file.

In the second step, oscap executes the fix scripts and verifies the result. It is safe to

store the results into the input file, no data will be lost. During offline remediation,

OpenSCAP creates a new TestResult element that is based on the input one and

inherits all the data. The newly created TestResult differs only in the rule-result

elements that have failed. For those, remediation is executed.

To perform offline remediation using the scap-security-guide package, run:

~]$ oscap xccdf eval --profile

xccdf_org.ssgproject.content_profile_rht-ccp --results scan-xccdf-

results.xml /usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml

~]$ oscap xccdf remediate --results scan-xccdf-results.xml scan-xccdf-

results.xml

6.4.6.3. OpenSCAP Remediation Review

The review mode allows users to store remediation instructions to a file for further

review. The remediation content is not executed during this operation.

To generate remediation instructions in the form of a shell script, run:

~]$ oscap xccdf generate fix --template urn:xccdf:fix:script:sh --

profile xccdf_org.ssgproject.content_profile_rht-ccp --output my-

remediation-script.sh /usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml

6.5. Using OpenSCAP with Docker

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6.5. Using OpenSCAP with Docker

The oscap-docker command-line utility allows users to use the oscap program to scan

their docker-formatted container images and containers almost in the same way as their

local systems.

The following section explains the installation of oscap-docker and offers basic examples

of usage. To learn more about sub-commands, use the --help option with the oscap-

docker or oscap commands.

To enable the scanning of images and containers, you need to have the docker package

installed, too. See the Getting Docker in Red Hat Enterprise Linux 7 chapter of the Getting

Started with Containers guide for instructions on installing Do cker.

enter the following command to install oscap-docker:

# yum install openscap-utils

Example 6.12. Using oscap-docker

oscap-docker scan_target[-cve] target_identifier [oscap-arguments]

Where scan_target is an image or a container to scan, and target_identifier is the name

or the ID of the target.

The second of the following commands attaches a container image, determines the

variant and version of the operating system, downloads the CVE stream applicable to

the given system, and finally runs the vulnerability scan:

# docker images

REPOSITORY TAG IMAGE ID

registry.access.redhat.com/rhel7 latest

c453594215e4

# oscap-docker image-cve registry.access.redhat.com/rhel7

The second of the following commands runs the OpenSCAP scan within a chroot

environment of a running container. The results may differ from scanning of a container

image due to defined mount points. We used the OVAL patch definition

com.redhat.rhsa-all.xml in this example.

# docker ps

CONTAINER ID IMAGE COMMAND NAMES

5ef05eef4a01 registry.access.redhat.com/rhel7 "/bin/bash"

sleepy_kirch

# oscap-docker container 5ef05eef4a01 oval eval com.redhat.rhsa-

all.xml

6.6. Using OpenSCAP with Atomic

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To verify all the container images and containers present on the system are free of

known CVE vulnerabilities or common misconfigurations, use the OpenSCAP scanning

capabilities through the atomic scan command.

Atomic Scan

To install the atomic tool on your system for container management, enter the following

command as root:

# yum install atomic

After the atomic tool is installed, you also need a scanner. Red Hat recommends choosing

the OpenSCAP-based rhel7/openscap docker image. Install it by running the following

command as root:

# atomic install rhel7/openscap

Once the OpenSCAP docker image is in place, you can issue atomic scan commands.

Scan the containers and container images by running the following command as root:

# atomic scan $ID

Where $ID is the ID of the container. If you want to scan all container images or

containers, use the --images or --containers directive, respectively. To scan both

types, use the --all directive.

T he OpenSCAP Scanner

The rhel7/openscap container image as the default scanner of the atomic scan currently

supports two scan types targeting Red Hat Enterprise Linux systems only. Supported scan

types can be listed by running the following command as root:

# atomic scan --scanner openscap --list

The default scan type is CVE scan. Use it for checking the target for known security

vulnerabilities as defined in the CVE OVAL definitions released by Red Hat.

Warning

The OVAL definitions used by the CVE scan type are bundled in the container image

during the build process, and as such are not always up-to-date.

The second supported scan type is standards_compliance, where Standard System

Security Profile of the bundled SCAP Security Guide is used for evaluation. This is security

baseline profile of Red Hat Enterprise Linux.

Example 6.13. Scanning t he Co nt ainer Image wit h At o mic Scan

The following example of the atomic scan usage shows how to scan a

Red Hat Enterprise Linux image and then list of all found vulnerabilities with --verbose

directive.

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# docker pull rhel7

Using default tag: latest

98a88a8b722a: Download complete

# atomic scan 98a88a8b722a

Container/Image Cri Imp Med Low

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

98a88a8b722a 0 0 0 0

# atomic scan --verbose 98a88a8b722a

docker run -t --rm -v /etc/localtime:/etc/localtime -v

/run/atomic/2016-10-14-06-42-55-991951:/scanin -v

/var/lib/atomic/openscap/2016-10-14-06-42-55-991951:/scanout:rw,Z -v

/etc/oscapd:/etc/oscapd:ro rhel7/openscap oscapd-evaluate scan --no-

standard-compliance --targets chroots-in-dir:///scanin --output

/scanout

INFO:OpenSCAP Daemon one-off evaluator 0.1.6

WARNING:Can't import the 'docker' package. Container scanning

functionality will be disabled.

INFO:Creating tasks directory at '/var/lib/oscapd/tasks' because it

didn't exist.

INFO:Creating results directory at '/var/lib/oscapd/results' because

it didn't exist.

INFO:Creating results work in progress directory at

'/var/lib/oscapd/work_in_progress' because it didn't exist.

INFO:Evaluated EvaluationSpec, exit_code=0.

INFO:[100.00%] Scanned target

'chroot:///scanin/98a88a8b722a71835dd761c88451c681a8f1bc6e577f90d4dc8b

234100bd4861'

98a88a8b722a (registry.access.redhat.com/rhel7:latest)

98a88a8b722a passed the scan

Files associated with this scan are in /var/lib/atomic/openscap/2016-

10-14-06-42-55-991951.

Note

A detailed description of the atomic command usage and containers is found in the

Product Documentation for Red Hat Enterprise Linux Atomic Host. The Red Hat

Customer Portal also provides a guide to the Atomic command line interface (CLI).

6.7. Using OpenSCAP with Red Hat Satellite

When running multiple Red Hat Enterprise Linux systems, it is important to keep all your

systems compliant with your security policy and perform security scans and evaluations

remotely from one location. This can be achieved by using Red Hat Satellite 5.5 or later

with the spacewalk-oscap package installed on your Satellite client. The package is

available from the Red Hat Net work Tools channel. See How to enable/disable a

repository using Red Hat Subscription-Manager?

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This solution supports two methods of performing security compliance scans, viewing and

further processing of the scan results. You can either use the OpenSCAP Satellite Web

Interface or run commands and scripts from the Satellite API. For more information

about this solution to security compliance, its requirements and capabilities, see the Red

Hat Satellite documentation.

6.8. Practical Examples

This section demonstrates practical usage of certain security content provided for Red Hat

products.

6.8.1. Auditing Securit y Vulnerabilit ies of Red Hat Product s

Red Hat continuously provides OVAL definitions for their products. These definitions allow

for fully automated audit of vulnerabilities in the installed software. To find out more

information about this project, see http://www.redhat.com/security/data/metrics/. To

download these definitions, enter the following command:

~]$ wget http://www.redhat.com/security/data/oval/com.redhat.rhsa-

all.xml

The users of Red Hat Satellite 5 may find useful the XCCDF part of the patch definitions.

To download these definitions, enter the following command:

~]$ wget http://www.redhat.com/security/data/metrics/com.redhat.rhsa-

all.xccdf.xml

To audit security vulnerabilities for the software installed on the system, enter the

following command:

~]$ oscap oval eval --results rhsa-results-oval.xml --report oval-

report.html com.redhat.rhsa-all.xml

The oscap utility maps Red Hat Security Advisories to CVE identifiers that are linked to

the National Vulnerability Database and reports which security advisories are not applied.

Note

Note that these OVAL definitions are designed to only cover software and updates

released by Red Hat. You need to provide additional definitions in order to detect

the patch status of third-party software.

6.8.2. Auditing System Set t ings with SCAP Security Guide

The SCAP Security Guide (SSG) project's package, scap-security-guide, contains the latest

set of security polices for Linux systems. To install the SCAP Security Guide package on

your system, enter the following command as root:

~]# yum install scap-security-guide

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A part of scap-security-guide is also a guidance for Red Hat Enterprise Linux 7 settings. To

inspect the security content available with scap-security-guide, use the oscap info

module:

~]$ oscap info /usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml

The output of this command is an outline of the SSG document and it contains available

configuration profiles. To audit your system settings, choose a suitable profile and run the

appropriate evaluation command. For example, the following command is used to assess

the given system against a draft SCAP profile for Red Hat Certified Cloud Providers:

~]$ oscap xccdf eval --profile xccdf_org.ssgproject.content_profile_rht-

ccp --results ssg-rhel7-xccdf-result.xml --report ssg-rhel7-report.html

/usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml

6.9. Additional Resources

For more information about various security compliance fields of interest, see the

resources below.

Installed Document ation

oscap(8) — The manual page for the oscap command-line utility provides a complete

list of available options and their usage explanation.

scap-workbench(8) — The manual page for the SCAP Workbench application provides a

basic information about the application as well as some links to potential sources of

SCAP content.

scap-security-guide(8) — The manual page for scap-securit y-guide provides further

documentation about the various available SCAP security profiles. Examples how to

utilize the provided benchmarks using the OpenSCAP utility are provided as well.

Online Document at ion

The OpenSCAP project page — The home page to the OpenSCAP project provides

detailed information about the o scap utility and other components and projects related

to SCAP.

The SCAP Workbench project page — The home page to the SCAP Workbench project

provides detailed information about the scap-wo rkbench application.

The SCAP Security Guide (SSG) project page — The home page to the SSG project that

provides the latest security content for Red Hat Enterprise Linux.

National Institute of Standards and Technology (NIST) SCAP page — This page

represents a vast collection of SCAP related materials, including SCAP publications,

specifications, and the SCAP Validation Program.

National Vulnerability Database (NVD) — This page represents the largest repository of

SCAP content and other SCAP standards based vulnerability management data.

Red Hat OVAL content repository — This is a repository containing OVAL definitions for

Red Hat Enterprise Linux systems.

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MITRE CVE — This is a database of publicly known security vulnerabilities provided by

the MITRE corporation.

MITRE OVAL — This page represents an OVAL related project provided by the MITRE

corporation. Amongst other OVAL related information, these pages contain the latest

version of the OVAL language and a huge repository of OVAL content, counting over 22

thousands OVAL definitions.

Red Hat Satellite documentation — This set of guides describes, amongst other topics,

how to maintain system security on multiple systems by using OpenSCAP.

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Chapter 7. Federal Standards and Regulations

In order to maintain security levels, it is possible for your organization to make efforts to

comply with federal and industry security specifications, standards and regulations. This

chapter describes some of these standards and regulations.

7.1. Federal Information Processing Standard (FIPS)

The Federal Information Processing Standard (FIPS) Publication 140-2 is a computer

security standard, developed by the U.S. Government and industry working group to

validate the quality of cryptographic modules. See the official FIPS publications here:

http://csrc.nist.gov/publications/PubsFIPS.html. At the time of the Red Hat Enterprise Linux

7.3 release, Publication 140-3 is at Draft status, and may not represent the completed

standard.

The FIPS 140-2 standard ensures that cryptographic tools implement their algorithms

properly. See the full FIPS 140-2 standard at http://csrc.nist.gov/publications/fips/fips140-

2/fips1402.pdf for further details on these levels and the other specifications of the FIPS

standard.

To see the complete list of all FIPS 140-2 certificates, visit

http://csrc.nist.gov/groups/STM/cmvp/documents/140-1/140val-all.htm. To learn about

compliance requirements, see the Red Hat Government: Standards page.

7.1.1. Enabling FIPS Mode

To make Red Hat Enterprise Linux compliant with the Federal Information Processing

Standard (FIPS) Publication 140-2, you need to make several changes to ensure that

accredited cryptographic modules are used. You can either enable FIPS mode during

system installation or after it.

During the System Installation

To fulfil the strict FIPS 140-2 compliance, add the fips=1 kernel option to the kernel

command line during system installation. With this option, all keys' generations are done

with FIPS-approved algorithms and continuous monitoring tests in place. After the

installation, the system is configured to boot into FIPS mode automatically.

Important

Ensure that the system has plenty of entropy during the installation process by

moving the mouse around or by pressing many keystrokes. The recommended

amount of keystrokes is 256 and more. Less than 256 keystrokes could generate a

non-unique key.

After the System Installation

To turn your system, kernel and user space, into FIPS mode anytime after the system

installation, follow these steps:

1. Make sure prelinking is disabled.

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For proper operation of the in-module integrity verification, prelinking of libraries

and binaries has to be disabled. Prelinking is done by the prelink package, which is

not installed by default. To disable prelinking, set the PRELINKING=no option in the

/etc/sysconfig/prelink configuration file. To disable existing prelinking on all

system files, use the prelink -u -a command.

2. Install the dracut-fips package:

~]# yum install dracut-fips

For the CPUs with the AES New Instructions (AES-NI) support, install the dracut-fips-

aesni package as well:

~]# yum install dracut-fips-aesni

3. Regenerate the initramfs file.

To enable the in-module integrity verification and to have all required modules

present during the kernel boot, the initramfs file has to be regenerated:

~]# dracut -v -f

Warning

This operation will overwrite the existing initramfs file.

4. Modify boot loader configuration.

To boot into FIPS mode, add the fips=1 option to the kernel command line of the

boot loader. If your /boot or /boot/EFI/ partitions reside on separate partitions,

add the boot=<partition> (where <partition> stands for /boot or /boot/EFI)

parameter to the kernel command line as well.

To identify the boot partition, enter the following command:

~]$ df /boot

Filesystem 1K-blocks Used Available Use% Mounted on

/dev/sda1 495844 53780 416464 12% /boot

To ensure that the boot= configuration option works even if the device naming

changes between boots, identify the universally unique identifier (UUID) of the

partition by running the following command:

~]$ blkid /dev/sda1

/dev/sda1: UUID="05c000f1-f899-467b-a4d9-d5ca4424c797" TYPE="ext4"

Append the UUID to the kernel command line:

boot=UUID=05c000f1-f899-467b-a4d9-d5ca4424c797

Depending on your boot loader, make the following changes:

⁠Chapte r 7. Federal Standards and Regulations

219

grub2

Add the fips=1 and boot=<partition of /boot or /boot/EFI> options to the

GRUB_CMDLINE_LINUX key in the /etc/default/grub file. To apply the changes

to /etc/default/grub, rebuild the grub.cfg file as follows:

On BIOS-based machines, enter the following command as root:

~]# grub2-mkconfig -o /boot/grub2/grub.cfg

On UEFI-based machines, enter the following command as root:

~]# grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg

zipl (on the IBM z Systems architecture only)

Add the fips=1 and boot=<partition of /boot> options to the

/etc/zipl.conf to the kernel command line and apply the changes by running

the following command as root:

~]# zipl

5. Reboot your system.

7.2. National Industrial Security Program Operating Manual

(NISPOM)

The NISPOM (also called DoD 5220.22-M), as a component of the National Industrial

Security Program (NISP), establishes a series of procedures and requirements for all

government contractors with regard to classified information. The current NISPOM is dated

February 28, 2006, with incorporated major changes from March 28, 2013. The NISPOM

document can be downloaded from the following URL: http://www.nispom.org/NISPOM-

download.html.

7.3. Payment Card Industry Data Security Standard (PCI

DSS)

From https://www.pcisecuritystandards.org/about/index.shtml: The PCI Security Standards

Council is an open global forum, launched in 2006, that is responsible for the development,

management, education, and awareness of the PCI Security Standards, including the Data

Security Standard (DSS).

You can download the PCI DSS standard from

https://www.pcisecuritystandards.org/security_standards/pci_dss.shtml.

7.4. Security Technical Implementation Guide

A Security Technical Implementation Guide (STIG) is a methodology for standardized

secure installation and maintenance of computer software and hardware.

See the following URL for more information on STIG:

http://iase.disa.mil/stigs/Pages/index.aspx.

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220

Appendix A. Encryption Standards

A.1. Synchronous Encryption

A.1.1. Advanced Encrypt ion St andard — AES

In cryptography, the Advanced Encryption Standard (AES) is an encryption standard

adopted by the U.S. Government. The standard comprises three block ciphers, AES-128,

AES-192 and AES-256, adopted from a larger collection originally published as Rijndael.

Each AES cipher has a 128-bit block size, with key sizes of 128, 192 and 256 bits,

respectively. The AES ciphers have been analyzed extensively and are now used

worldwide, as was the case with its predecessor, the Data Encryption Standard (DES). ⁠

A.1.1.1. AES History

AES was announced by National Institute of Standards and Technology (NIST) as U.S. FIPS

PUB 197 (FIPS 197) on November 26, 2001 after a 5-year standardization process. Fifteen

competing designs were presented and evaluated before Rijndael was selected as the

most suitable. It became effective as a standard May 26, 2002. It is available in many

different encryption packages. AES is the first publicly accessible and open cipher

approved by the NSA for top secret information (see the Security section in the Wikipedia

article on AES). ⁠

The Rijndael cipher was developed by two Belgian cryptographers, Joan Daemen and

Vincent Rijmen, and submitted by them to the AES selection process. Rijndael is a

portmanteau of the names of the two inventors. ⁠

A.1.2. Data Encryption St andard — DES

The Data Encryption Standard (DES) is a block cipher (a form of shared secret encryption)

that was selected by the National Bureau of Standards as an official Federal Information

Processing Standard (FIPS) for the United States in 1976 and which has subsequently

enjoyed widespread use internationally. It is based on a symmetric-key algorithm that

uses a 56-bit key. The algorithm was initially controversial with classified design

elements, a relatively short key length, and suspicions about a National Security Agency

(NSA) backdoor. DES consequently came under intense academic scrutiny which motivated

the modern understanding of block ciphers and their cryptanalysis. ⁠

A.1.2.1. DES History

DES is now considered to be insecure for many applications. This is chiefly due to the 56-

bit key size being too small; in January, 1999, distributed.net and the Electronic Frontier

Foundation collaborated to publicly break a DES key in 22 hours and 15 minutes. There are

also some analytical results which demonstrate theoretical weaknesses in the cipher,

although they are unfeasible to mount in practice. The algorithm is believed to be

practically secure in the form of Triple DES, although there are theoretical attacks. In

recent years, the cipher has been superseded by the Advanced Encryption Standard

(AES). ⁠

In some documentation, a distinction is made between DES as a standard and DES the

algorithm which is referred to as the DEA (the Data Encryption Algorithm). ⁠

[3]

[4]

[5]

[6]

[7]

[8]

⁠Appe ndix A. Encryption Standards

221

A.2. Public-key Encryption

Public-key cryptography is a cryptographic approach, employed by many cryptographic

algorithms and cryptosystems, whose distinguishing characteristic is the use of

asymmetric key algorithms instead of or in addition to symmetric key algorithms. Using

the techniques of public key-private key cryptography, many methods of protecting

communications or authenticating messages formerly unknown have become practical.

They do not require a secure initial exchange of one or more secret keys as is required

when using symmetric key algorithms. It can also be used to create digital signatures. ⁠

Public key cryptography is a fundamental and widely used technology around the world,

and is the approach which underlies such Internet standards as Transport Layer Security

(TLS) (successor to SSL), PGP and GPG. ⁠

The distinguishing technique used in public key cryptography is the use of asymmetric key

algorithms, where the key used to encrypt a message is not the same as the key used to

decrypt it. Each user has a pair of cryptographic keys — a public key and a private key.

The private key is kept secret, whilst the public key may be widely distributed. Messages

are encrypted with the recipient's public key and can only be decrypted with the

corresponding private key. The keys are related mathematically, but the private key

cannot be feasibly (ie, in actual or projected practice) derived from the public key. It was

the discovery of such algorithms which revolutionized the practice of cryptography

beginning in the middle 1970s. ⁠

In contrast, Symmetric-key algorithms, variations of which have been used for some

thousands of years, use a single secret key shared by sender and receiver (which must

also be kept private, thus accounting for the ambiguity of the common terminology) for

both encryption and decryption. To use a symmetric encryption scheme, the sender and

receiver must securely share a key in advance. ⁠

Because symmetric key algorithms are nearly always much less computationally

intensive, it is common to exchange a key using a key-exchange algorithm and transmit

data using that key and a symmetric key algorithm. PGP, and the SSL/TLS family of

schemes do this, for instance, and are called hybrid cryptosystems in consequence. ⁠

A.2.1. Diffie-Hellman

Diffie–Hellman key exchange (D–H) is a cryptographic protocol that allows two parties that

have no prior knowledge of each other to jointly establish a shared secret key over an

insecure communications channel. This key can then be used to encrypt subsequent

communications using a symmetric key cipher. ⁠

A.2.1.1. Diff ie-Hellman History

The scheme was first published by Whitfield Diffie and Martin Hellman in 1976, although it

later emerged that it had been separately invented a few years earlier within GCHQ, the

British signals intelligence agency, by Malcolm J. Williamson but was kept classified. In

2002, Hellman suggested the algorithm be called Diffie–Hellman–Merkle key exchange in

recognition of Ralph Merkle's contribution to the invention of public-key cryptography

(Hellman, 2002). ⁠

[9]

[10]

[11]

[12]

[13]

[14]

[15]

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Although Diffie–Hellman key agreement itself is an anonymous (non-authenticated) key-

agreement protocol, it provides the basis for a variety of authenticated protocols, and is

used to provide perfect forward secrecy in Transport Layer Security's ephemeral modes

(referred to as EDH or DHE depending on the cipher suite). ⁠

U.S. Patent 4,200,770, now expired, describes the algorithm and credits Hellman, Diffie,

and Merkle as inventors. ⁠

A.2.2. RSA

In cryptography, RSA (which stands for Rivest, Shamir and Adleman who first publicly

described it) is an algorithm for public-key cryptography. It is the first algorithm known to

be suitable for signing as well as encryption, and was one of the first great advances in

public key cryptography. RSA is widely used in electronic commerce protocols, and is

believed to be secure given sufficiently long keys and the use of up-to-date

implementations.

A.2.3. DSA

DSA (Digital Signature Algorithm) is a standard for digital signatures, a United States

federal government standard for digital signatures. DSA is for signatures only and is not

an encryption algorithm. ⁠

A.2.4. SSL/T LS

Transport Layer Security (TLS) and its predecessor, Secure Sockets Layer (SSL), are

cryptographic protocols that provide security for communications over networks such as

the Internet. TLS and SSL encrypt the segments of network connections at the Transport

Layer end-to-end.

Several versions of the protocols are in widespread use in applications like web browsing,

electronic mail, Internet faxing, instant messaging and voice-over-IP (VoIP). ⁠

A.2.5. Cramer-Shoup Cryptosystem

The Cramer–Shoup system is an asymmetric key encryption algorithm, and was the first

efficient scheme proven to be secure against adaptive chosen ciphertext attack using

standard cryptographic assumptions. Its security is based on the computational

intractability (widely assumed, but not proved) of the decisional Diffie–Hellman assumption.

Developed by Ronald Cramer and Victor Shoup in 1998, it is an extension of the ElGamal

cryptosystem. In contrast to ElGamal, which is extremely malleable, Cramer–Shoup adds

additional elements to ensure non-malleability even against a resourceful attacker. This

non-malleability is achieved through the use of a collision-resistant hash function and

additional computations, resulting in a ciphertext which is twice as large as in ElGamal.

A.2.6. ElGamal Encryption

In cryptography, the ElGamal encryption system is an asymmetric key encryption

algorithm for public-key cryptography which is based on the Diffie-Hellman key agreement.

It was described by Taher ElGamal in 1985. ElGamal encryption is used in the free GNU

Privacy Guard software, recent versions of PGP, and other cryptosystems. ⁠

[16]

[17]

[18]

[19]

[20]

[21]

⁠Appe ndix A. Encryption Standards

223

[3] "Advanced Encryption Standard." Wikipedia. 14 Novem ber 2009
http://en.wikipedia.org/wiki/Advanced_Encryption_Standard
[4] "Advanced Encryption Standard." Wikipedia. 14 Novem ber 2009
http://en.wikipedia.org/wiki/Advanced_Encryption_Standard
[5] "Advanced Encryption Standard." Wikipedia. 14 November 2009
http://en.wikipedia.org/wiki/Advanced_Encryption_Standard
[6] "Data Encryption Standard." Wikipedia. 14 Novem ber 2009
http://en.wikipedia.org/wiki/Data_Encryption_Standard
[7] "Data Encryption Standard." Wikipedia. 14 Novem ber 2009
http://en.wikipedia.org/wiki/Data_Encryption_Standard
[8] "Data Encryption Standard." Wikipedia. 14 Novem ber 2009
http://en.wikipedia.org/wiki/Data_Encryption_Standard
[9] "Public-key Encryption." Wikipedia. 14 November 2009 http://en.wikipedia.org/wiki/Public-
key_cryptography
[10] "Public-key Encryption." Wikipedia. 14 Novem ber 2009 http://en.wikipedia.org/wiki/Public-
key_cryptography
[11] "Public-key Encryption." Wikipedia. 14 Novem ber 2009 http://en.wikipedia.org/wiki/Public-
key_cryptography
[12] "Public-key Encryption." Wikipedia. 14 November 2009 http://en.wikipedia.org/wiki/Public-
key_cryptography
[13] "Public-key Encryption." Wikipedia. 14 Novem ber 2009 http://en.wikipedia.org/wiki/Public-
key_cryptography
[14] "Diffie-Hellman." Wikipedia. 14 Novem ber 2009 http://en.wikipedia.org/wiki/Diffie-Hellm an
[15] "Diffie-Hellman." Wikipedia. 14 Novem ber 2009 http://en.wikipedia.org/wiki/Diffie-Hellm an
[16] "Diffie-Hellman." Wikipedia. 14 Novem ber 2009 http://en.wikipedia.org/wiki/Diffie-Hellm an
[17] "Diffie-Hellman." Wikipedia. 14 Novem ber 2009 http://en.wikipedia.org/wiki/Diffie-Hellm an
[18] "DSA." Wikipedia. 24 February 2010 http://en.wikipedia.org/wiki/Digital_Signature_Algorithm
[19] "TLS/SSL." Wikipedia. 24 February 2010 http://en.wikipedia.org/wiki/Transport_Layer_Security
[20] "Cramer-Shoup cryptosystem." Wikipedia. 24 February 2010
http://en.wikipedia.org/wiki/Cramer–Shoup_cryptosystem
[21] "ElGamal encryption" Wikipedia. 24 February 2010
http://en.wikipedia.org/wiki/ElGamal_encryption
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Appendix B. Audit System Reference

B.1. Audit Event Fields

Table B.1, “Event Fields” lists all currently-supported Audit event fields. An event field is

the value preceding the equal sign in the Audit log files.

Table B.1. Event Fields

Event Field Explanat io n

a0, a1, a2, a3 Records the first four arguments of the system call, encoded

in hexadecimal notation.

acct Records a user's account name.

addr Records the IPv4 or IPv6 address. This field usually follows a

hostname field and contains the address the host name

resolves to.

arch Records information about the CPU architecture of the system,

encoded in hexadecimal notation.

auid Records the Audit user ID. This ID is assigned to a user upon

identity changes (for example, by switching user accounts with

su - john).

capability Records the number of bits that were used to set a particular

Linux capability. For more information on Linux capabilities,

see the capabilities(7) man page.

cap_fi Records data related to the setting of an inherited file

system-based capability.

cap_fp Records data related to the setting of a permitted file system-

based capability.

cap_pe Records data related to the setting of an effective process-

based capability.

cap_pi Records data related to the setting of an inherited process-

based capability.

cap_pp Records data related to the setting of a permitted process-

based capability.

cgroup Records the path to the cgroup that contains the process at

the time the Audit event was generated.

cmd Records the entire command line that is executed. This is

useful in case of shell interpreters where the exe field

records, for example, /bin/bash as the shell interpreter and

the cmd field records the rest of the command line that is

executed, for example helloworld.sh --help.

comm Records the command that is executed. This is useful in case

of shell interpreters where the exe field records, for example,

/bin/bash as the shell interpreter and the comm field records

the name of the script that is executed, for example

helloworld.sh.

cwd Records the path to the directory in which a system call was

invoked.

data Records data associated with TTY records.

dev Records the minor and major ID of the device that contains

the file or directory recorded in an event.

⁠Appe ndix B. Audit System Ref e rence

225

devmajor Records the major device ID.

devminor Records the minor device ID.

egid Records the effective group ID of the user who started the

analyzed process.

euid Records the effective user ID of the user who started the

analyzed process.

exe Records the path to the executable that was used to invoke

the analyzed process.

exit Records the exit code returned by a system call. This value

varies by system call. You can interpret the value to its

human-readable equivalent with the following command:

ausearch --interpret --exit exit_code

family Records the type of address protocol that was used, either

IPv4 or IPv6.

filetype Records the type of the file.

flags Records the file system name flags.

fsgid Records the file system group ID of the user who started the

analyzed process.

fsuid Records the file system user ID of the user who started the

analyzed process.

gid Records the group ID.

hostname Records the host name.

icmptype Records the type of a Internet Control Message Protocol

(ICMP) package that is received. Audit messages containing

this field are usually generated by ipt ables.

id Records the user ID of an account that was changed.

inode Records the inode number associated with the file or directory

recorded in an Audit event.

inode_gid Records the group ID of the inode's owner.

inode_uid Records the user ID of the inode's owner.

items Records the number of path records that are attached to this

record.

key Records the user defined string associated with a rule that

generated a particular event in the Audit log.

list Records the Audit rule list ID. The following is a list of known

IDs:

0 — user

1 — task

4 — exit

5 — exclude

mode Records the file or directory permissions, encoded in

numerical notation.

msg Records a time stamp and a unique ID of a record, or various

event-specific <name>=<value> pairs provided by the kernel

or user space applications.

msgtype Records the message type that is returned in case of a user-

based AVC denial. The message type is determined by D-

Bus.

name Records the full path of the file or directory that was passed

to the system call as an argument.

Event Field Explanat io n

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new-disk Records the name of a new disk resource that is assigned to

a virtual machine.

new-mem Records the amount of a new memory resource that is

assigned to a virtual machine.

new-vcpu Records the number of a new virtual CPU resource that is

assigned to a virtual machine.

new-net Records the MAC address of a new network interface

resource that is assigned to a virtual machine.

new_gid Records a group ID that is assigned to a user.

oauid Records the user ID of the user that has logged in to access

the system (as opposed to, for example, using su) and has

started the target process. This field is exclusive to the

record of type OBJ_PID.

ocomm Records the command that was used to start the target

process.This field is exclusive to the record of type OBJ_PID.

opid Records the process ID of the target process. This field is

exclusive to the record of type OBJ_PID.

oses Records the session ID of the target process. This field is

exclusive to the record of type OBJ_PID.

ouid Records the real user ID of the target process

obj Records the SELinux context of an object. An object can be a

file, a directory, a socket, or anything that is receiving the

action of a subject.

obj_gid Records the group ID of an object.

obj_lev_high Records the high SELinux level of an object.

obj_lev_low Records the low SELinux level of an object.

obj_role Records the SELinux role of an object.

obj_uid Records the UID of an object

obj_user Records the user that is associated with an object.

ogid Records the object owner's group ID.

old-disk Records the name of an old disk resource when a new disk

resource is assigned to a virtual machine.

old-mem Records the amount of an old memory resource when a new

amount of memory is assigned to a virtual machine.

old-vcpu Records the number of an old virtual CPU resource when a

new virtual CPU is assigned to a virtual machine.

old-net Records the MAC address of an old network interface

resource when a new network interface is assigned to a

virtual machine.

old_prom Records the previous value of the network promiscuity flag.

ouid Records the real user ID of the user who started the target

process.

path Records the full path of the file or directory that was passed

to the system call as an argument in case of AVC-related

Audit events

perm Records the file permission that was used to generate an

event (that is, read, write, execute, or attribute change)

Event Field Explanat io n

⁠Appe ndix B. Audit System Ref e rence

227

pid The pid field semantics depend on the origin of the value in

this field.

In fields generated from user-space, this field holds a process

ID.

In fields generated by the kernel, this field holds a thread ID.

The thread ID is equal to process ID for single-threaded

processes. Note that the value of this thread ID is different

from the values of pthread_t IDs used in user-space. For

more information, see the gettid(2) man page.

ppid Records the Parent Process ID (PID).

prom Records the network promiscuity flag.

proto Records the networking protocol that was used. This field is

specific to Audit events generated by ipt ables.

res Records the result of the operation that triggered the Audit

event.

result Records the result of the operation that triggered the Audit

event.

saddr Records the socket address.

sauid Records the sender Audit login user ID. This ID is provided by

D-Bus as the kernel is unable to see which user is sending

the original auid.

ses Records the session ID of the session from which the

analyzed process was invoked.

sgid Records the set group ID of the user who started the

analyzed process.

sig Records the number of a signal that causes a program to end

abnormally. Usually, this is a sign of a system intrusion.

subj Records the SELinux context of a subject. A subject can be a

process, a user, or anything that is acting upon an object.

subj_clr Records the SELinux clearance of a subject.

subj_role Records the SELinux role of a subject.

subj_sen Records the SELinux sensitivity of a subject.

subj_user Records the user that is associated with a subject.

success Records whether a system call was successful or failed.

suid Records the set user ID of the user who started the analyzed

process.

syscall Records the type of the system call that was sent to the

kernel.

terminal Records the terminal name (without /dev/).

tty Records the name of the controlling terminal. The value

(none) is used if the process has no controlling terminal.

uid Records the real user ID of the user who started the analyzed

process.

vm Records the name of a virtual machine from which the Audit

event originated.

Event Field Explanat io n

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B.2. Audit Record Types
Table B.2, “Record Types” lists all currently-supported types of Audit records. The event
type is specified in the type= field at the beginning of every Audit record.
Table B.2. Record Types
Event  T ype Explanat io n
ADD_GROUP Triggered when a user-space group is added.
ADD_USER Triggered when a user-space user account is added.
ANOM_ABEND ⁠ Triggered when a processes ends abnormally (with a signal
that could cause a core dump, if enabled).
ANOM_ACCESS_FS[a] Triggered when a file or a directory access ends abnormally.
ANOM_ADD_ACCT[a] Triggered when a user-space account addition ends
abnormally.
ANOM_AMTU_FAIL[a] Triggered when a failure of the Abstract Machine Test Utility
(AMTU) is detected.
ANOM_CRYPTO_FAIL[a] Triggered when a failure in the cryptographic system is
detected.
ANOM_DEL_ACCT[a] Triggered when a user-space account deletion ends
abnormally.
ANOM_EXEC[a] Triggered when an execution of a file ends abnormally.
ANOM_LOGIN_ACCT[a] Triggered when an account login attempt ends abnormally.
ANOM_LOGIN_FAILURES[
a]
Triggered when the limit of failed login attempts is reached.
ANOM_LOGIN_LOCATION[
a]
Triggered when a login attempt is made from a forbidden
location.
ANOM_LOGIN_SESSIONS[
a]
Triggered when a login attempt reaches the maximum amount
of concurrent sessions.
ANOM_LOGIN_TIME[a] Triggered when a login attempt is made at a time when it is
prevented by, for example, pam_time.
ANOM_MAX_DAC[a] Triggered when the maximum amount of Discretionary Access
Control (DAC) failures is reached.
ANOM_MAX_MAC[a] Triggered when the maximum amount of Mandatory Access
Control (MAC) failures is reached.
ANOM_MK_EXEC[a] Triggered when a file is made executable.
ANOM_MOD_ACCT[a] Triggered when a user-space account modification ends
abnormally.
ANOM_PROMISCUOUS[a] Triggered when a device enables or disables promiscuous
mode.
ANOM_RBAC_FAIL[a] Triggered when a Role-Based Access Control (RBAC) self-test
failure is detected.
ANOM_RBAC_INTEGRITY_
FAIL[a]
Triggered when a Role-Based Access Control (RBAC) file
integrity test failure is detected.
ANOM_ROOT_TRANS[a] Triggered when a user becomes root.
AVC Triggered to record an SELinux permission check.
AVC_PATH Triggered to record the dentry and vfsmount pair when an
SELinux permission check occurs.
[a]
⁠Appe ndix B. Audit System Ref e rence
229

BPRM_FCAPS Triggered when a user executes a program with a file system

capability.

CAPSET Triggered to record the capabilities being set for process-

based capabilities, for example, running as root to drop

capabilities.

CHGRP_ID Triggered when a user-space group ID is changed.

CHUSER_ID Triggered when a user-space user ID is changed.

CONFIG_CHANGE Triggered when the Audit system configuration is modified.

CRED_ACQ Triggered when a user acquires user-space credentials.

CRED_DISP Triggered when a user disposes of user-space credentials.

CRED_REFR Triggered when a user refreshes their user-space

credentials.

CRYPTO_FAILURE_USER Triggered when a decrypt, encrypt, or randomize

cryptographic operation fails.

CRYPTO_KEY_USER Triggered to record the cryptographic key identifier used for

cryptographic purposes.

CRYPTO_LOGIN Triggered when a cryptographic officer login attempt is

detected.

CRYPTO_LOGOUT Triggered when a cryptographic officer logout attempt is

detected.

CRYPTO_PARAM_CHANGE_

USER

Triggered when a change in a cryptographic parameter is

detected.

CRYPTO_REPLAY_USER Triggered when a replay attack is detected.

CRYPTO_SESSION Triggered to record parameters set during a TLS session

establishment.

CRYPTO_TEST_USER Triggered to record cryptographic test results as required by

the FIPS-140 standard.

CWD Triggered to record the current working directory.

DAC_CHECK Triggered to record DAC check results.

DAEMON_ABORT Triggered when a daemon is stopped due to an error.

DAEMON_ACCEPT Triggered when the auditd daemon accepts a remote

connection.

DAEMON_CLOSE Triggered when the auditd daemon closes a remote

connection.

DAEMON_CONFIG Triggered when a daemon configuration change is detected.

DAEMON_END Triggered when a daemon is successfully stopped.

DAEMON_RESUME Triggered when the auditd daemon resumes logging.

DAEMON_ROTATE Triggered when the auditd daemon rotates the Audit log

files.

DAEMON_START Triggered when the auditd daemon is started.

DEL_GROUP Triggered when a user-space group is deleted

DEL_USER Triggered when a user-space user is deleted

DEV_ALLOC Triggered when a device is allocated.

DEV_DEALLOC Triggered when a device is deallocated.

EOE Triggered to record the end of a multi-record event.

EXECVE Triggered to record arguments of the execve(2) system call.

FD_PAIR Triggered to record the use of the pipe and socketpair

system calls.

FS_RELABEL Triggered when a file system relabel operation is detected.

Event T ype Explanat io n

Securit y Guide

230

GRP_AUTH Triggered when a group password is used to authenticate

against a user-space group.

INTEGRITY_DATA ⁠ Triggered to record a data integrity verification event run by

the kernel.

INTEGRITY_HASH[b] Triggered to record a hash type integrity verification event

run by the kernel.

INTEGRITY_METADATA[b] Triggered to record a metadata integrity verification event run

by the kernel.

INTEGRITY_PCR[b] Triggered to record Platform Configuration Register (PCR)

invalidation messages.

INTEGRITY_RULE[b] Triggered to record a policy rule.

INTEGRITY_STATUS[b] Triggered to record the status of integrity verification.

IPC Triggered to record information about a Inter-Process

Communication object referenced by a system call.

IPC_SET_PERM Triggered to record information about new values set by an

IPC_SET control operation on an IPC object.

KERNEL Triggered to record the initialization of the Audit system.

KERNEL_OTHER Triggered to record information from third-party kernel

modules.

LABEL_LEVEL_CHANGE Triggered when an object's level label is modified.

LABEL_OVERRIDE Triggered when an administrator overrides an object's level

label.

in to access the system.

MAC_CIPSOV4_ADD Triggered when a Commercial Internet Protocol Security

Option (CIPSO) user adds a new Domain of Interpretation

(DOI). Adding DOIs is a part of the packet labeling capabilities

of the kernel provided by NetLabel.

MAC_CIPSOV4_DEL Triggered when a CIPSO user deletes an existing DOI. Adding

DOIs is a part of the packet labeling capabilities of the kernel

provided by NetLabel.

MAC_CONFIG_CHANGE Triggered when an SELinux Boolean value is changed.

MAC_IPSEC_EVENT Triggered to record information about an IPSec event, when

one is detected, or when the IPSec configuration changes.

MAC_MAP_ADD Triggered when a new Linux Security Module (LSM) domain

mapping is added. LSM domain mapping is a part of the packet

labeling capabilities of the kernel provided by NetLabel.

MAC_MAP_DEL Triggered when an existing LSM domain mapping is added.

LSM domain mapping is a part of the packet labeling

capabilities of the kernel provided by NetLabel.

MAC_POLICY_LOAD Triggered when a SELinux policy file is loaded.

MAC_STATUS Triggered when the SELinux mode (enforcing, permissive, off)

is changed.

MAC_UNLBL_ALLOW Triggered when unlabeled traffic is allowed when using the

packet labeling capabilities of the kernel provided by NetLabel.

MAC_UNLBL_STCADD Triggered when a static label is added when using the packet

labeling capabilities of the kernel provided by NetLabel.

MAC_UNLBL_STCDEL Triggered when a static label is deleted when using the

packet labeling capabilities of the kernel provided by NetLabel.

MMAP Triggered to record a file descriptor and flags of the mmap(2)

system call.

Event T ype Explanat io n

[b]

⁠Appe ndix B. Audit System Ref e rence

231

MQ_GETSETATTR Triggered to record the mq_getattr(3) and mq_setattr(3)

message queue attributes.

MQ_NOTIFY Triggered to record arguments of the mq_notify(3) system

call.

MQ_OPEN Triggered to record arguments of the mq_open(3) system

call.

MQ_SENDRECV Triggered to record arguments of the mq_send(3) and

mq_receive(3) system calls.

NETFILTER_CFG Triggered when Netfilter chain modifications are detected.

NETFILTER_PKT Triggered to record packets traversing Netfilter chains.

OBJ_PID Triggered to record information about a process to which a

signal is sent.

PATH Triggered to record file name path information.

RESP_ACCT_LOCK ⁠ Triggered when a user account is locked.

RESP_ACCT_LOCK_TIMED

[c]

Triggered when a user account is locked for a specified period

of time.

RESP_ACCT_REMOTE[c] Triggered when a user account is locked from a remote

session.

RESP_ACCT_UNLOCK_TIM

ED[c]

Triggered when a user account is unlocked after a configured

period of time.

RESP_ALERT[c] Triggered when an alert email is sent.

RESP_ANOMALY[c] Triggered when an anomaly was not acted upon.

RESP_EXEC[c] Triggered when an intrusion detection program responds to a

threat originating from the execution of a program.

RESP_HALT[c] Triggered when the system is shut down.

RESP_KILL_PROC[c] Triggered when a process is terminated.

RESP_SEBOOL[c] Triggered when an SELinux Boolean value is set.

RESP_SINGLE[c] Triggered when the system is put into single-user mode.

RESP_TERM_ACCESS[c] Triggered when a session is terminated.

RESP_TERM_LOCK[c] Triggered when a terminal is locked.

ROLE_ASSIGN Triggered when an administrator assigns a user to an SELinux

role.

ROLE_MODIFY Triggered when an administrator modifies an SELinux role.

ROLE_REMOVE Triggered when an administrator removes a user from an

SELinux role.

SELINUX_ERR Triggered when an internal SELinux error is detected.

SERVICE_START Triggered when a service is started.

SERVICE_STOP Triggered when a service is stopped.

SOCKADDR Triggered to record a socket address.

SOCKETCALL Triggered to record arguments of the sys_socketcall

system call (used to multiplex many socket-related system

calls).

SYSCALL Triggered to record a system call to the kernel.

SYSTEM_BOOT Triggered when the system is booted up.

SYSTEM_RUNLEVEL Triggered when the system's run level is changed.

SYSTEM_SHUTDOWN Triggered when the system is shut down.

TEST Triggered to record the success value of a test message.

Event T ype Explanat io n

[c]

Securit y Guide

232

TRUSTED_APP The record of this type can be used by third party application

that require auditing.

TTY Triggered when TTY input was sent to an administrative

process.

USER_ACCT Triggered when a user-space user account is modified.

USER_AUTH Triggered when a user-space authentication attempt is

detected.

USER_AVC Triggered when a user-space AVC message is generated.

USER_CHAUTHTOK Triggered when a user account attribute is modified.

USER_CMD Triggered when a user-space shell command is executed.

USER_END Triggered when a user-space session is terminated.

USER_ERR Triggered when a user account state error is detected.

USER_LABELED_EXPORT Triggered when an object is exported with an SELinux label.

USER_LOGIN Triggered when a user logs in.

USER_LOGOUT Triggered when a user logs out.

USER_MAC_POLICY_LOAD Triggered when a user-space daemon loads an SELinux policy.

USER_MGMT Triggered to record user-space management data.

USER_ROLE_CHANGE Triggered when a user's SELinux role is changed.

USER_SELINUX_ERR Triggered when a user-space SELinux error is detected.

USER_START Triggered when a user-space session is started.

USER_TTY Triggered when an explanatory message about TTY input to

an administrative process is sent from user-space.

USER_UNLABELED_EXPOR

Triggered when an object is exported without SELinux label.

USYS_CONFIG Triggered when a user-space system configuration change is

detected.

VIRT_CONTROL Triggered when a virtual machine is started, paused, or

stopped.

VIRT_MACHINE_ID Triggered to record the binding of a label to a virtual machine.

VIRT_RESOURCE Triggered to record resource assignment of a virtual machine.

Event T ype Explanat io n

[a] All Audit event types prepended with ANOM are intended to be processed by an intrusion

detection program.

[b] This event type is related to the Integrity Measurement Architecture (IMA), which functions

best with a Trusted Platform Module (TPM) chip.

[c] All Audit event types prepended with RESP are intended responses of an intrusion

detection system in case it detects malicious activity on the system.

⁠Appe ndix B. Audit System Ref e rence

233

Appendix C. Revision History

Revisio n 1-24 Mo n Feb 6 20 17 Mirek Jahoda

Async release with misc. updates, especially in the firewalld section.

Revisio n 1-23 Tue Nov 1 2016 Mirek Jahoda

Version for 7.3 GA publication.

Revisio n 1-19 Mo n Jul 18 20 16 Mirek Jahoda

The Smart Cards section added.

Revisio n 1-18 Mo n Jun 27 2016 Mirek Jahoda

The OpenSCAP-daemon and Atomic Scan section added.

Revisio n 1-17 Fri Jun 3 2016 Mirek Jahoda

Async release with misc. updates.

Revisio n 1-16 Tue Jan 5 2016 Ro bert Krát ký

Post 7.2 GA fixes.

Revisio n 1-15 Tue Nov 10 20 15 Ro bert Krát ký

Version for 7.2 GA release.

Revisio n 1-14.18 Mo n Nov 09 2015 Ro bert Krát ký

Async release with misc. updates.

Revisio n 1-14.17 Wed Feb 18 2015 Robert Krátký

Version for 7.1 GA release.

Revisio n 1-14.15 Fri Dec 06 20 14 Ro bert Krát ký

Update to sort order on the Red Hat Customer Portal.

Revisio n 1-14.13 Thu Nov 27 2014 Robert Krát ký

Updates reflecting the POODLE vuln.

Revisio n 1-14.12 Tue Jun 03 20 14 To máš Čapek

Version for 7.0 GA release.

Securit y Guide

234

Security Guide Red Hat Enterprise Linux 7

Red%20Hat%20Enterprise%20Linux%207%20Security%20Guide

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