Title

RHEL 9 must not accept router advertisements on all IPv6 interfaces by default. (Cat II impact)

Discussion

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

Check Content

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: $ 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 Text

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

Additional Identifiers

Rule ID: SV-257975r925912_rule

Vulnerability ID: V-257975

Group Title: SRG-OS-000480-GPOS-00227

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