Vulnerability Discussion

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-routerd 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.

Check

Verify RHEL 9 will not accept IPv4 source-routed packets.

Check the value of the all "accept_source_route" variables with the following command:

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

net.ipv4.conf.all.accept_source_route = 0

If the returned line does not have a value of "0", 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.accept_source_route | tail -1

net.ipv4.conf.all.accept_source_route = 0

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

Fix

Configure RHEL 9 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 with the following command:

$ sudo sysctl --system