Vulnerability Discussion

An illicit router advertisement message could result in a man-in-the-middle attack.

Check

Verify RHEL 9 does not accept router advertisements on all IPv6 interfaces by default, unless the system is a router.

Note: If IPv6 is disabled on the system, this requirement is Not Applicable.

Determine if router advertisements are not accepted by default by using the following command:

$ sudo sysctl net.ipv6.conf.default.accept_ra

net.ipv6.conf.default.accept_ra = 0

If the "accept_ra" value is not "0" and is not documented with the information system security officer (ISSO) as an operational requirement, 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.ipv6.conf.default.accept_ra | tail -1

net.ipv6.conf.default.accept_ra = 0

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

Fix

Configure RHEL 9 to not accept router advertisements on all IPv6 interfaces by default 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.default.accept_ra = 0

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

$ sudo sysctl --system