AlmaLinux OS 9 must log packets with impossible addresses.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-269251 | ALMA-09-019380 | SV-269251r1050133_rule | CCI-000366 | medium |
| Description | ||||
| The presence of "martian" packets (which have impossible addresses) as well as spoofed packets, source-routed packets, and redirects could be a sign of nefarious network activity. Logging these packets enables this activity to be detected. | ||||
| STIG | Date | |||
| CloudLinux AlmaLinux OS 9 Security Technical Implementation Guide | 2025-05-22 | |||
Details
Check Text (C-269251r1050133_chk)
Verify AlmaLinux OS 9 logs martian packets.
Check the value of the "log_martians" variables with the following command:
$ sysctl -a | grep log_martians
net.ipv4.conf.all.log_martians = 1
net.ipv4.conf.default.log_martians = 1
net.ipv4.conf.enp1s0.log_martians = 1
net.ipv4.conf.lo.log_martians = 1
If the returned lines do not all have a value of "1", this is a finding.
Fix Text (F-73183r1049385_fix)
Configure AlmaLinux OS 9 to log martian packets.
Create a numbered *.conf file in /etc/sysctl.d/ with the following content:
net.ipv4.conf.all.log_martians = 1
net.ipv4.conf.default.log_martians = 1
net.ipv4.conf.lo.log_martians = 1
The system configuration files need to be reloaded for the changes to take effect. To reload the contents of the files, run the following command:
$ sysctl --system