IP forwarding for IPv4 must not be enabled, unless the system is a router.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-12023	GEN005600	SV-37929r1_rule	ECSC-1	Medium

Description
If the system is configured for IP forwarding and is not a designated router, it could be used to bypass network security by providing a path for communication not filtered by network devices.

STIG	Date
Red Hat Enterprise Linux 5 Security Technical Implementation Guide	2017-03-01

Details

Check Text ( C-37179r1_chk )
Check if the system is configured for IPv4 forwarding. If the system is a VM host and acts as a router solely for the benefits of its client systems, then this rule is not applicable. Procedure: # cat /proc/sys/net/ipv4/ip_forward If the value is set to "1", IPv4 forwarding is enabled this is a finding.

Fix Text (F-32422r1_fix)
Edit "/etc/sysctl.conf" and set net.ipv4.ip_forward to "0". Restart the system or run "sysctl -p" to make the change take effect.