IT Best Practices Tip: nist_V-38529

Severity: medium

Short Description

The system must not accept IPv4 source-routed packets by default.

Long Description

Accepting source-routed packets in 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_source_route" kernel parameter can be queried by running the following command:

$ sysctl net.ipv4.conf.default.accept_source_route

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_source_route /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_source_route" kernel parameter, run the following command:

# sysctl -w net.ipv4.conf.default.accept_source_route=0

If this is not the system's default value, add the following line to "/etc/sysctl.conf":

net.ipv4.conf.default.accept_source_route = 0