RHEL 9 must not respond to Internet Control Message Protocol (ICMP) echoes sent to a broadcast address.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-257966	RHEL-09-253055	SV-257966r942995_rule		Medium

Description
Responding to broadcast (ICMP) echoes facilitates network mapping and provides a vector for amplification attacks. Ignoring ICMP echo requests (pings) sent to broadcast or multicast addresses makes the system slightly more difficult to enumerate on the network.

STIG	Date
Red Hat Enterprise Linux 9 Security Technical Implementation Guide	2023-12-01

Details

Check Text ( C-61707r942994_chk )

Verify RHEL 9 does not respond to ICMP echoes sent to a broadcast address. Check the value of the "icmp_echo_ignore_broadcasts" variable with the following command: $ sudo sysctl net.ipv4.icmp_echo_ignore_broadcasts net.ipv4.icmp_echo_ignore_broadcasts = 1 If the returned line does not have a value of "1", a line is not returned, or the retuned line is commented out, this is a finding. Check that the configuration files are present to enable this network parameter. $ sudo /usr/lib/systemd/systemd-sysctl --cat-config | egrep -v '^(#|$)' | grep -F net.ipv4.icmp_echo_ignore_broadcasts | tail -1 net.ipv4.icmp_echo_ignore_broadcasts = 1 If "net.ipv4.icmp_echo_ignore_broadcasts" is not set to "1" or is missing, this is a finding.

Fix Text (F-61631r925884_fix)
Configure RHEL 9 to not respond to IPv4 ICMP echoes sent to a broadcast address. Add or edit the following line in a single system configuration file, in the "/etc/sysctl.d/" directory: net.ipv4.icmp_echo_ignore_broadcasts = 1 Load settings from all system configuration files with the following command: $ sudo sysctl --system