TOSS 5 must ignore Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirect messages.
Severity | Group ID | Group Title | Version | Rule ID | Date | STIG Version |
|---|---|---|---|---|---|---|
| medium | V-282685 | SRG-OS-000480-GPOS-00227 | TOSS-05-000213 | SV-282685r1201035_rule | 2026-04-01 | 1 |
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 IPv4 protocol has few legitimate uses. It should be disabled unless absolutely required.
ℹ️ Check
Verify TOSS 5 will not accept IPv4 ICMP redirect messages using the following command:
$ sudo sysctl net.ipv4.conf.all.accept_redirects
net.ipv4.conf.all.accept_redirects = 0
If the returned line does not have a value of "0", or a line is not returned, this is a finding.
✔️ Fix
Configure TOSS 5 to ignore IPv4 ICMP redirect messages.
Add or edit the following line in a single system configuration file, in the "/etc/sysctl.d/" directory:
net.ipv4.conf.all.accept_redirects = 0
Load settings from all system configuration files using the following command:
$ sudo sysctl --system