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The Ubuntu operating system must ignore Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirect messages.


Overview

Finding ID Version Rule ID IA Controls Severity
V-215150 UBTU-16-030570 SV-215150r610931_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 modify the host's route table and are unauthenticated. An illicit ICMP redirect message could result in a man-in-the-middle attack.
STIG Date
Canonical Ubuntu 16.04 LTS Security Technical Implementation Guide 2020-12-09

Details

Check Text ( C-16349r285318_chk )
Verify the Ubuntu operating system ignores Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirect messages.

Check the value of the "accept_redirects" variables with the following command:

# sudo sysctl net.ipv4.conf.all.accept_redirects

net.ipv4.conf.all.accept_redirects=0

If both of the returned lines do not have a value of "0", or a line is not returned, this is a finding.
Fix Text (F-16347r285319_fix)
Configure the Ubuntu operating system to ignore Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirect messages with the following command:

# sudo sysctl -w net.ipv4.conf.all.accept_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.accept_redirects=0