IT Best Practices Tip: nist_V-38529
The system must not accept IPv4 source-routed packets by default.
Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required.
How to Check Correct Configuration
The status of the "net.ipv4.conf.default.accept_source_route" kernel parameter can be queried by running the following command:
$ sysctl net.ipv4.conf.default.accept_source_route
The output of the command should indicate a value of "0". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf".
$ grep net.ipv4.conf.default.accept_source_route /etc/sysctl.conf
If the correct value is not returned, this is a finding.
How to Fix
To set the runtime status of the "net.ipv4.conf.default.accept_source_route" kernel parameter, run the following command:
# sysctl -w net.ipv4.conf.default.accept_source_route=0
If this is not the system's default value, add the following line to "/etc/sysctl.conf":
net.ipv4.conf.default.accept_source_route = 0