The Oracle Linux operating system must prevent Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirect messages from being accepted.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-221878	OL07-00-040640	SV-221878r880651_rule		Medium

Description
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
Oracle Linux 7 Security Technical Implementation Guide	2023-03-06

Details

Check Text ( C-23593r880649_chk )
Verify the system will not accept IPv4 ICMP redirect messages. # grep -r net.ipv4.conf.default.accept_redirects /run/sysctl.d/* /etc/sysctl.d/* /usr/local/lib/sysctl.d/* /usr/lib/sysctl.d/* /lib/sysctl.d/* /etc/sysctl.conf 2> /dev/null If "net.ipv4.conf.default.accept_redirects" is not configured in the /etc/sysctl.conf file or in any of the other sysctl.d directories, is commented out, or does not have a value of "0", this is a finding. Check that the operating system implements the value of the "accept_redirects" variables with the following command: # /sbin/sysctl -a \| grep net.ipv4.conf.default.accept_redirects net.ipv4.conf.default.accept_redirects = 0 If the returned line does not have a value of "0", this is a finding. If conflicting results are returned, this is a finding.

Check Text ( C-23593r880649_chk )

Verify the system will not accept IPv4 ICMP redirect messages.

# grep -r net.ipv4.conf.default.accept_redirects /run/sysctl.d/* /etc/sysctl.d/* /usr/local/lib/sysctl.d/* /usr/lib/sysctl.d/* /lib/sysctl.d/* /etc/sysctl.conf 2> /dev/null

If "net.ipv4.conf.default.accept_redirects" is not configured in the /etc/sysctl.conf file or in any of the other sysctl.d directories, is commented out, or does not have a value of "0", this is a finding.

Check that the operating system implements the value of the "accept_redirects" variables with the following command:

# /sbin/sysctl -a | grep net.ipv4.conf.default.accept_redirects
net.ipv4.conf.default.accept_redirects = 0

If the returned line does not have a value of "0", this is a finding.

If conflicting results are returned, this is a finding.

Fix Text (F-23582r880650_fix)
Set the system to not accept IPv4 ICMP redirect messages by adding the following line to "/etc/sysctl.conf" or a configuration file in the /etc/sysctl.d/ directory (or modify the line to have the required value): net.ipv4.conf.default.accept_redirects = 0 Issue the following command to make the changes take effect: # sysctl --system