Vulnerability Discussion

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.

Check

Verify RHEL 9 logs IPv4 martian packets.

Check the value of the accept source route variable with the following command:

$ sudo sysctl net.ipv4.conf.all.log_martians

net.ipv4.conf.all.log_martians = 1

If the returned line does not have a value of "1", a line is not returned, or the line is commented out, this is a finding.

Check that the configuration files are present to enable this network parameter.

$ sudo /usr/lib/systemd/systemd-sysctl --cat-config | egrep -v '^(#|;)' | grep -F net.ipv4.conf.all.log_martians | tail -1

net.ipv4.conf.all.log_martians = 1

If "net.ipv4.conf.all.log_martians" is not set to "1" or is missing, this is a finding.

Fix

Configure RHEL 9 to log martian packets on IPv4 interfaces.

Add or edit the following line in a single system configuration file, in the "/etc/sysctl.d/" directory:

net.ipv4.conf.all.log_martians=1

Load settings from all system configuration files with the following command:

$ sudo sysctl --system