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V-204613

CAT II (Medium)

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

Rule ID

SV-204613r991589_rule

STIG

Red Hat Enterprise Linux 7 Security Technical Implementation Guide

Version

V3R15

CCIs

CCI-000366

Discussion

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

Check Content

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

     # grep -r net.ipv4.icmp_echo_ignore_broadcasts /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.icmp_echo_ignore_broadcasts" 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 "1", this is a finding.

Check that the operating system implements 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", this is a finding.

If conflicting results are returned, this is a finding.

Fix Text

Set the system to the required kernel parameter 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.icmp_echo_ignore_broadcasts = 1

Issue the following command to make the changes take effect: 

     # sysctl --system