The system must use a reverse-path filter for IPv4 network traffic when possible on all interfaces.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-38542	RHEL-06-000096	SV-50343r2_rule		Medium

Description
Enabling reverse path filtering drops packets with source addresses that should not have been able to be received on the interface they were received on. It should not be used on systems which are routers for complicated networks, but is helpful for end hosts and routers serving small networks.

STIG	Date
Red Hat Enterprise Linux 6 Security Technical Implementation Guide	2016-06-05

Details

Check Text ( C-46100r2_chk )
The status of the "net.ipv4.conf.all.rp_filter" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.conf.all.rp_filter The output of the command should indicate a value of "1". 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.all.rp_filter /etc/sysctl.conf If the correct value is not returned, this is a finding.

Check Text ( C-46100r2_chk )

The status of the "net.ipv4.conf.all.rp_filter" kernel parameter can be queried by running the following command:

$ sysctl net.ipv4.conf.all.rp_filter

The output of the command should indicate a value of "1". 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.all.rp_filter /etc/sysctl.conf

If the correct value is not returned, this is a finding.

Fix Text (F-43490r1_fix)
To set the runtime status of the "net.ipv4.conf.all.rp_filter" kernel parameter, run the following command: # sysctl -w net.ipv4.conf.all.rp_filter=1 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.conf.all.rp_filter = 1