The Ubuntu operating system must not send Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirects.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-75885	UBTU-16-030590	SV-90565r2_rule		Medium

Description
Internet Control Message Protocol (ICMP) redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages contain information from the system's route table, possibly revealing portions of the network topology.

STIG	Date
Canonical Ubuntu 16.04 Security Technical Implementation Guide	2020-05-29

Details

Check Text ( C-75573r2_chk )

Verify the Ubuntu operating system does not send Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirect messages. Check the value of the "all send_redirects" variables with the following command: # sudo sysctl net.ipv4.conf.all.send_redirects net.ipv4.conf.all.send_redirects=0 If the returned line does not have a value of "0", or a line is not returned, this is a finding.

Fix Text (F-82515r2_fix)

Configure the Ubuntu operating system to not allow interfaces to perform Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirects with the following command: # sudo sysctl -w net.ipv4.conf.all.send_redirects=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.all.send_redirects=0