TOSS 5 must log IPv4 packets with impossible addresses by default.

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.

Verify TOSS 5 logs IPv4 martian packets by default using the following command:

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

net.ipv4.conf.default.log_martians = 1

If "net.ipv4.conf.default.log_martians" is not set to "1" , or a line is not returned, this is a finding.

Configure TOSS 5 to log martian packets on IPv4 interfaces by default.

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

net.ipv4.conf.default.log_martians=1

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

$ sudo sysctl --system