RHEL 9 must use reverse path filtering on all IPv4 interfaces.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-257962	RHEL-09-253035	SV-257962r942989_rule		Medium

Description
Enabling reverse path filtering drops packets with source addresses that should not have been able to be received on the interface on which they were received. It must not be used on systems that are routers for complicated networks, but is helpful for end hosts and routers serving small networks.

STIG	Date
Red Hat Enterprise Linux 9 Security Technical Implementation Guide	2023-12-01

Details

Check Text ( C-61703r942988_chk )

Verify RHEL 9 uses reverse path filtering on all IPv4 interfaces with the following commands: $ sudo sysctl net.ipv4.conf.all.rp_filter net.ipv4.conf.all.rp_filter = 1 If the returned line does not have a value of "1", or a line is not returned, 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.rp_filter | tail -1 net.ipv4.conf.all.rp_filter = 1 If "net.ipv4.conf.all.rp_filter" is not set to "1" or is missing, this is a finding.

Fix Text (F-61627r925872_fix)
Configure RHEL 9 to use reverse path filtering on all IPv4 interfaces. Add or edit the following line in a single system configuration file, in the "/etc/sysctl.d/" directory: net.ipv4.conf.all.rp_filter = 1 The system configuration files need to be reloaded for the changes to take effect. To reload the contents of the files, run the following command: $ sudo sysctl --system