RHEL 10 must prevent Internet Protocol version 6 (IPv6) Internet Control Message Protocol (ICMP) redirect messages from being accepted.

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.

Satisfies: SRG-OS-000420-GPOS-00186, SRG-OS-000142-GPOS-00090

Note: If IPv6 is disabled on the system, this requirement is not applicable.

Verify RHEL 10 prevents IPv6 ICMP redirect messages from being accepted.

Check the value of the "net.ipv6.conf.default.accept_redirects" variables with the following command:

$ sudo sysctl net.ipv6.conf.default.accept_redirects net.ipv6.conf.default.accept_redirects = 0

If "net.ipv6.conf.default.accept_redirects" is not set to "0" or is missing, this is a finding.

Configure RHEL 10 to prevent IPv6 ICMP redirect messages from being accepted.

Create a configuration file if it does not already exist:

$ sudo vi /etc/sysctl.d/ipv6_accept_redirects.conf

Add the following line to the file:

net.ipv6.conf.default.accept_redirects = 0

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

$ sudo sysctl --system