Lynis : Security Auditing Tool for Unix/Linux Systems

Lynis is a security auditing tool for UNIX derivatives like Linux, macOS, BSD, Solaris, AIX, and others. It performs an in-depth security scan. It is used by system administrators, auditors and security professionals, all over the world. Some of the features are:

Basics

Open source
Shell script
No dependencies
Easy to understand

Support

Dynamic OS detection
300+ built-in tests
Support for custom tests
Plugin support
Compliance checks
Extensive software support

Reporting

Report on screen and details in report file
Reporting of warnings and suggestions
Detailed logging
Hardening index

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Installation via Git

Clone project

The first step is cloning the project. Before doing so, select the parent directory. Git will create a ‘lynis’ subdirectory with the full program in it.

$ cd /usr/local
$ git clone https://github.com/CISOfy/lynis
Cloning into ‘lynis’…
remote: Counting objects: 1733, done.
remote: Compressing objects: 100% (8/8), done.
remote: Total 1733 (delta 3), reused 0 (delta 0), pack-reused 1725
Receiving objects: 100% (1733/1733), 886.18 KiB | 378.00 KiB/s, done.
Resolving deltas: 100% (1204/1204), done.
Checking connectivity… done.
$ cd lynis

That is it. Time to run your first security audit:

$ lynis audit system

Although no configuration is required, there are a few useful commands to learn.

Running Lynis

Ensure that you are in the right directory and add ‘./’ in front of the command, like:

$ ./lynis

Lynis can run without any preconfiguration. Configuration and fine-tuning is possible though and will be covered in later sections. For now we will run a basic scan:

$ lynis audit system

(use ./lynis audit system to start Lynis from the local directory if you didn’t install it as a software package)

Lynis and pauses

By default Lynis starts and pauses after the first section. With CTRL+C you can stop the program. With ENTER it will continue to the next set of tests.

If we want to run Lynis without any pauses, we could give it an additional parameter: –quick. This will enable the “quick” option, ideal for running Lynis while you do other things.

$ lynis audit system –quick

Report and Logging

Lynis performs an in-depth audit and reports its findings to the following outputs:

Screen
Logging
Report

1. Screen output

Lynis scans the system and performs hundreds of tests. For most of these tests, a result will be displayed on the screen.

Possible tests results include:

OK or Warning
Found or Not found
A value

2. Log file

The results are displayed on screen during the system scan. Additional details are logged in a separate file (default: /var/log/lynis.log). This information is useful for advanced testers, to see what the program did in the background, or where anomalies showed up.

Information in the log file

Time of an action/event
Reason(s) why a test failed or was skipped
Output of (internal) tests
Suggestions about configuration options or how to fix/improve things
Threat/impact score

Remark: the log file is purged every scan. If you need debugging or logging information for previous scans, schedule log rotation or make a backup before running Lynis again.

3. Report files

During the audit process, Lynis will gather findings and other data points. This information is stored in the report file, which is by default /var/log/lynis-report.dat.

Lynis supports one report format, which can be used to gather results and display them in a custom or (more) friendly presentation. The report file can also be used to compare scan results from the past with a current scan. Lynis Enterprise has much more possibilities to display data, including extended reports in several formats.

Contents of report file:

Remarks = #<remark>
Section = [<section name>]
Option/value = <option name>=<value of option>

When an option could have multiple values (like installed packages for example), brackets ([]) are added. Example: installed_package[]=Package-1.0.0

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