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

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-215147	UBTU-16-030540	SV-215147r610931_rule		Medium

Description
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.

STIG	Date
Canonical Ubuntu 16.04 LTS Security Technical Implementation Guide	2020-12-09

Details

Check Text ( C-16346r285309_chk )

Verify the Ubuntu operating system does not accept Internet Protocol version 4 (IPv4) source-routed packets by default. Check the value of the accept source route variable with the following command: # sudo sysctl 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 (F-16344r285310_fix)

Configure the Ubuntu operating system to not forward Internet Protocol version 4 (IPv4) source-routed packets by default with the following command: # sudo sysctl -w net.ipv4.conf.default.accept_source_route=0 If "0" is not the system's default value then add or update the following line in "/etc/sysctl.conf" or in the appropriate file under "/etc/sysctl.d": net.ipv4.conf.default.accept_source_route=0