TOSS 5 must not forward Internet Protocol version 4 (IPv4) source-routed packets.

Source-routed packets allow the source of the packet to suggest routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures. This requirement applies only to the forwarding of source-routed traffic, such as when IPv4 forwarding is enabled and the system is functioning as a router.

Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It must be disabled unless it is absolutely required.

Verify TOSS 5 will not accept IPv4 source-routed packets using the following command:

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

net.ipv4.conf.all.accept_source_route = 0

If "net.ipv4.conf.all.accept_source_route" is not set to "0", or a line is not returned, this is a finding.

Configure TOSS 5 to ignore IPv4 source-routed packets.

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

net.ipv4.conf.all.accept_source_route = 0

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

$ sudo sysctl --system