AlmaLinux OS 9 must ignore Internet Control Message Protocol (ICMP) redirect messages.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-269244 | ALMA-09-018610 | SV-269244r1050126_rule | Medium |
| Description |
| 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 IP protocol has few legitimate uses. It should be disabled unless absolutely required. |
| STIG | Date |
| CloudLinux AlmaLinux OS 9 Security Technical Implementation Guide | 2025-05-22 |
Details
| Check Text (C-73275r1049367_chk) |
| Verify AlmaLinux OS 9 will not accept ICMP redirect messages. Check the value of the "accept_redirects" variables with the following command: $ sysctl -a | grep accept_redirects net.ipv4.conf.all.accept_redirects = 0 net.ipv4.conf.default.accept_redirects = 0 net.ipv4.conf.enp1s0.accept_redirects = 0 net.ipv4.conf.lo.accept_redirects = 0 net.ipv6.conf.all.accept_redirects = 0 net.ipv6.conf.default.accept_redirects = 0 net.ipv6.conf.enp1s0.accept_redirects = 0 net.ipv6.conf.lo.accept_redirects = 0 If the returned lines do not all have a value of "0", this is a finding. |
| Fix Text (F-73176r1049368_fix) |
| Configure AlmaLinux OS 9 to ignore ICMP redirect messages. Create a numbered *.conf file in /etc/sysctl.d/ with the following content: net.ipv4.conf.all.accept_redirects = 0 net.ipv4.conf.default.accept_redirects = 0 net.ipv4.conf.lo.accept_redirects = 0 net.ipv6.conf.all.accept_redirects = 0 net.ipv6.conf.default.accept_redirects = 0 net.ipv6.conf.lo.accept_redirects = 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 |