RHEL 9 must not accept router advertisements on all IPv6 interfaces. GROUP ID: V-257971 RULE ID: SV-257971r991589 An illicit router advertisement message could result in a man-in-the-middle attack.
Solution
Configure RHEL 9 to not accept router advertisements on all IPv6 interfaces unless the system is a router. Add or edit the following line in a single system configuration file, in the "/etc/sysctl.d/" directory: net.ipv6.conf.all.accept_ra = 0 Load settings from all system configuration files with the following command: $ sudo sysctl --system