The system must not respond to Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) echoes sent to a broadcast address.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-72287	RHEL-07-040630	SV-86911r1_rule		Medium

Description
Responding to broadcast (ICMP) echoes facilitates network mapping and provides a vector for amplification attacks.

STIG	Date
Red Hat Enterprise Linux 7 Security Technical Implementation Guide	2017-12-14

Details

Check Text ( C-72521r1_chk )
Verify the system does not respond to IPv4 ICMP echoes sent to a broadcast address. Check the value of the "icmp_echo_ignore_broadcasts" variable with the following command: # /sbin/sysctl -a \| grep 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 Text ( C-72521r1_chk )

Verify the system does not respond to IPv4 ICMP echoes sent to a broadcast address.

Check the value of the "icmp_echo_ignore_broadcasts" variable with the following command:

# /sbin/sysctl -a | grep 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.

Fix Text (F-78641r1_fix)
Set the system to the required kernel parameter by adding the following line to "/etc/sysctl.conf" (or modify the line to have the required value): net.ipv4.icmp_echo_ignore_broadcasts=1