AlmaLinux OS 9 must not accept router advertisements on all IPv6 interfaces.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-269243 | ALMA-09-018500 | SV-269243r1050125_rule | Medium |
| Description |
| An illicit router advertisement message could result in a man-in-the-middle attack. |
| STIG | Date |
| CloudLinux AlmaLinux OS 9 Security Technical Implementation Guide | 2025-05-22 |
Details
| Check Text (C-73274r1049364_chk) |
| Note: If IPv6 is disabled on the system, this requirement is Not Applicable. Verify AlmaLinux OS 9 does not accept router advertisements on any IPv6 interfaces, unless the system is a router. Determine if router advertisements are not accepted by using the following command: $ sysctl -a | grep 'accept_ra ' net.ipv6.conf.all.accept_ra = 1 net.ipv6.conf.default.accept_ra = 1 net.ipv6.conf.enp1s0.accept_ra = 0 net.ipv6.conf.lo.accept_ra = 1 If any of the returned lines are not set to "0" and it is not documented with the information system security officer (ISSO) as an operational requirement, this is a finding. |
| Fix Text (F-73175r1049365_fix) |
| Configure AlmaLinux OS 9 to not accept router advertisements on all IPv6 interfaces unless the system is a router. Create a numbered *.conf file in /etc/sysctl.d/ with the following content: net.ipv6.conf.all.accept_ra = 0 net.ipv6.conf.default.accept_ra = 0 net.ipv6.conf.lo.accept_ra = 0 The system configuration files need to be reloaded for the changes to take effect. To reload the contents of the files, run the following command: $ sysctl –system |