IT Best Practices Tip: nist_V-38533
The system must ignore ICMPv4 redirect messages by default.
This feature of the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required.
How to Check Correct Configuration
The status of the "net.ipv4.conf.default.accept_redirects" kernel parameter can be queried by running the following command:
$ sysctl net.ipv4.conf.default.accept_redirects
The output of the command should indicate a value of "0". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf".
$ grep net.ipv4.conf.default.accept_redirects /etc/sysctl.conf
If the correct value is not returned, this is a finding.
How to Fix
To set the runtime status of the "net.ipv4.conf.default.accept_redirects" kernel parameter, run the following command:
# sysctl -w net.ipv4.conf.default.accept_redirects=0
If this is not the system's default value, add the following line to "/etc/sysctl.conf":
net.ipv4.conf.default.accept_redirects = 0