IT Best Practices Tip: nist_V-38600
The system must not send ICMPv4 redirects by default.
Sending ICMP redirects permits the system to instruct other systems to update their routing information. The ability to send ICMP redirects is only appropriate for systems acting as routers.
How to Check Correct Configuration
The status of the "net.ipv4.conf.default.send_redirects" kernel parameter can be queried by running the following command:
$ sysctl net.ipv4.conf.default.send_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.send_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.send_redirects" kernel parameter, run the following command:
# sysctl -w net.ipv4.conf.default.send_redirects=0
If this is not the system's default value, add the following line to "/etc/sysctl.conf":
net.ipv4.conf.default.send_redirects = 0