Alma Linux OS 9 must not accept IPv4 source-routed packets by default.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-269259 | ALMA-09-020260 | SV-269259r1107619_rule | CCI-000366 | medium |
| Description | ||||
| Source-routed packets allow the source of the packet to suggest routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures. This requirement applies only to the forwarding of source-routed traffic, such as when IP forwarding is enabled and the system is functioning as a router. Accepting source-routed packets has few legitimate uses. It must be disabled unless it is absolutely required. | ||||
| STIG | Date | |||
| CloudLinux AlmaLinux OS 9 Security Technical Implementation Guide | 2025-05-22 | |||
Details
Check Text (C-269259r1107619_chk)
Verify AlmaLinux OS 9 will not accept source-routed packets.
Check the value of the "accept_source_route" variables with the following command:
$ sysctl -a | grep accept_source_route
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0
net.ipv4.conf.enp1s0.accept_source_route = 0
net.ipv4.conf.lo.accept_source_route = 0
net.ipv6.conf.all.accept_source_route = 0
net.ipv6.conf.default.accept_source_route = 0
net.ipv6.conf.enp1s0.accept_source_route = 0
net.ipv6.conf.lo.accept_source_route = 0
If the returned lines do not all have a value of "0", this is a finding.
Fix Text (F-73191r1101841_fix)
Configure AlmaLinux OS 9 to ignore source-routed packets.
Create a numbered *.conf file in /etc/sysctl.d/ with the following content:
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0
net.ipv4.conf.lo.accept_source_route = 0
net.ipv6.conf.all.accept_source_route = 0
net.ipv6.conf.default.accept_source_route = 0
net.ipv6.conf.lo.accept_source_route = 0
The system configuration files must be reloaded for the changes to take effect. To reload the contents of the files, run the following command:
$ sysctl --system