ALMA-09-018610 - AlmaLinux OS 9 must ignore Internet Control Message Protocol (ICMP) redirect messages.

Information

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.

Solution

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

See Also

https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_CL_AlmaLinux_OS_9_V1R2_STIG.zip

Item Details

Category: CONFIGURATION MANAGEMENT

References: 800-53|CM-6b., CAT|II, CCI|CCI-000366, Rule-ID|SV-269244r1050126_rule, STIG-ID|ALMA-09-018610, Vuln-ID|V-269244

Plugin: Unix

Control ID: 9ca7802f3dabc28e7ee191a4e1fe099e26e978ce7bb16e176af3d4f52f202de2