How to scan Linux for vulnerabilities with lynis

As a system administrator, Linux security technician or system auditor, your responsibility can involve any combination of these: software patch management, malware scanning, file integrity checks, security audit, configuration error checking, etc. If there is an automatic vulnerability scanning tool, it can save you a lot of time checking up on common security issues.

One such vulnerability scanner on Linux is lynis. This tool is open-source (GPLv3), and actually supported on multiple platforms including Linux, FreeBSD, and Mac OS.

To install lynis on Linux, do the following.

$ wget http://cisofy.com/files/lynis-1.6.3.tar.gz
$ sudo tar xvfvz lynis-1.6.3.tar.gz -C /opt

To scan Linux for vulnerabilities with lynis, run the following.

$ cd /opt/lynis-1.6.3/
$ sudo ./lynis --check-all -Q

Once lynis starts scanning your system, it will perform auditing in a number of categories:

  • System tools: system binaries
  • Boot and services: boot loaders, startup services
  • Kernel: run level, loaded modules, kernel configuration, core dumps
  • Memory and processes: zombie processes, IO waiting processes
  • Users, groups and authentication: group IDs, sudoers, PAM configuration, password aging, default mask
  • Shells
  • File systems: mount points, /tmp files, root file system
  • Storage: usb-storage, firewire ohci
  • NFS
  • Software: name services: DNS search domain, BIND
  • Ports and packages: vulnerable/upgradable packages, security repository
  • Networking: nameservers, promiscuous interfaces, connections
  • Printers and spools: cups configuration
  • Software: e-mail and messaging
  • Software: firewalls: iptables, pf
  • Software: webserver: Apache, nginx
  • SSH support: SSH configuration
  • SNMP support
  • Databases: MySQL root password
  • LDAP services
  • Software: php: php options
  • Squid support
  • Logging and files: syslog daemon, log directories
  • Insecure services: inetd
  • Banners and identification
  • Scheduled tasks: crontab/cronjob, atd
  • Accounting: sysstat data, auditd
  • Time and synchronization: ntp daemon
  • Cryptography: SSL certificate expiration
  • Virtualization
  • Security frameworks: AppArmor, SELinux, grsecurity status
  • Software: file integrity
  • Software: malware scanners
  • Home directories: shell history files

The screenshot of lynis in action is shown below:

Once scanning is completed, the auditing report of your system is generated and stored in /var/log/lynis.log.

The audit report contains warnings for potential vulnerabilities detected by the tool. For example:

$ sudo grep Warning /var/log/lynis.log
[20:20:04] Warning: Root can directly login via SSH [test:SSH-7412] [impact:M]
[20:20:04] Warning: PHP option expose_php is possibly turned on, which can reveal useful information for attackers. [test:PHP-2372] [impact:M]
[20:20:06] Warning: No running NTP daemon or available client found [test:TIME-3104] [impact:M]

The audit report also contains a number of suggestions that can help harden your Linux system. For example:

$ sudo grep Suggestion /var/log/lynis.log
[20:19:41] Suggestion: Install a PAM module for password strength testing like pam_cracklib or pam_passwdqc [test:AUTH-9262]
[20:19:41] Suggestion: When possible set expire dates for all password protected accounts [test:AUTH-9282]
[20:19:41] Suggestion: Configure password aging limits to enforce password changing on a regular base [test:AUTH-9286]
[20:19:41] Suggestion: Default umask in /etc/profile could be more strict like 027 [test:AUTH-9328]
[20:19:42] Suggestion: Default umask in /etc/login.defs could be more strict like 027 [test:AUTH-9328]
[20:19:42] Suggestion: Default umask in /etc/init.d/rc could be more strict like 027 [test:AUTH-9328]
[20:19:42] Suggestion: To decrease the impact of a full /tmp file system, place /tmp on a separated partition [test:FILE-6310]
[20:19:42] Suggestion: Disable drivers like USB storage when not used, to prevent unauthorized storage or data theft [test:STRG-1840]
[20:19:42] Suggestion: Disable drivers like firewire storage when not used, to prevent unauthorized storage or data theft [test:STRG-1846]
[20:20:03] Suggestion: Install package apt-show-versions for patch management purposes [test:PKGS-7394]
. . . .

Scan Your System for Vulnerabilities as a Daily Cron Job

To get the most out of lynis, it’s recommended to run it on a regular basis, for example, as a daily cronjob. When run with "--cronjob" option, lynis runs in automatic, non-interactive scan mode.

The following is a daily cronjob script that runs lynis in automatic mode to audit your system, and archives daily scan reports.

$ sudo vi /etc/cron.daily/scan.sh
#!/bin/sh

AUDITOR="automated"
DATE=$(date +%Y%m%d)
HOST=$(hostname)
LOG_DIR="/var/log/lynis"
REPORT="$LOG_DIR/report-${HOST}.${DATE}"
DATA="$LOG_DIR/report-data-${HOST}.${DATE}.txt"

cd /opt/lynis-1.6.3
./lynis -c --auditor "${AUDITOR}" --cronjob > ${REPORT}

mv /var/log/lynis-report.dat ${DATA}
$ sudo chmod 755 /etc/cron.daily/scan.sh


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Dan Nanni is the founder and also a regular contributor of Xmodulo.com. He is a Linux/FOSS enthusiast who loves to get his hands dirty with his Linux box. He likes to procrastinate when he is supposed to be busy and productive. When he is otherwise free, he likes to watch movies and shop for the coolest gadgets.
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