The system must not forward Internet Protocol version 4 (IPv4) source-routed packets by default.

From Red Hat Enterprise Linux 7 Security Technical Implementation Guide

Associated with: CCI-000366

SV-86909r1_rule The system must not forward Internet Protocol version 4 (IPv4) source-routed packets by default.

Vulnerability discussion

Source-routed packets allow the source of the packet to suggest that routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures. This requirement applies only to the forwarding of source-routed traffic, such as when IPv4 forwarding is enabled and the system is functioning as a router.

Check content

Verify the system does not accept IPv4 source-routed packets by default. Check the value of the accept source route variable with the following command: # /sbin/sysctl -a | grep net.ipv4.conf.default.accept_source_route net.ipv4.conf.default.accept_source_route=0 If the returned line does not have a value of "0", a line is not returned, or the returned line is commented out, this is a finding.

Fix text

Set the system to the required kernel parameter by adding the following line to "/etc/sysctl.conf" (or modify the line to have the required value): net.ipv4.conf.default.accept_source_route = 0

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