RHEL 10 must ignore Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirect messages.

ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages modify the host's route table and are unauthenticated. An illicit ICMP redirect message could result in a man-in-the-middle attack. This feature of the IPv4 protocol has few legitimate uses. It should be disabled unless absolutely required. Satisfies: SRG-OS-000420-GPOS-00186, SRG-OS-000142-GPOS-00072

Verify RHEL 10 will not accept IPv4 ICMP redirect messages. Check the value of all "net.ipv4.conf.all.accept_redirects" variables with the following command: $ sudo sysctl net.ipv4.conf.all.accept_redirects net.ipv4.conf.all.accept_redirects = 0 If "net.ipv4.conf.all.accept_redirects" is not set to "0" or is missing, this is a finding.

Configure RHEL 10 to ignore IPv4 ICMP redirect messages. Create a configuration file if it does not already exist: $ sudo vi /etc/sysctl.d/99-ipv4_accept_redirects.conf Add the following line to the file: net.ipv4.conf.all.accept_redirects = 0 Reload settings from all system configuration files with the following command: $ sudo sysctl --system