RHEL 9 must not forward IPv4 source-routed packets by default.

Documentable No

Rule ID SV-257964r1155739_rule

CCI References

CCI-000366

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-routed traffic, such as when forwarding is enabled and the system is functioning as a router. The sysctl --system command will load settings from all system configuration files. All configuration files are sorted by their filename in lexicographical order, regardless of the directories in which they reside. If multiple files specify the same option, the entry in the file with the lexicographically latest name will take precedence. Files are read from directories in the following list from top to bottom. Once a file of a given filename is loaded, any file of the same name in subsequent directories is ignored. /etc/sysctl.d/*.conf /run/sysctl.d/*.conf /usr/local/lib/sysctl.d/*.conf /usr/lib/sysctl.d/*.conf /lib/sysctl.d/*.conf /etc/sysctl.conf

Check Procedure

Verify RHEL 9 does not accept IPv4 source-routed packets by default.

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

$ sudo sysctl net.ipv4.conf.default.accept_source_route
net.ipv4.conf.default.accept_source_route = 0

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

Fix Action

Configure RHEL 9 to not forward IPv4 source-routed packets by default.

Create a configuration file if it does not already exist:

$ sudo vi /etc/sysctl.d/99-ipv4_accept_source_route.conf

Add the following line to the file:
net.ipv4.conf.default.accept_source_route = 0

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

$ sudo sysctl --system