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.

From Red Hat Enterprise Linux 7 Security Technical Implementation Guide

Associated with: CCI-000366

SV-86911r2_rule 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.

Vulnerability 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 net.ipv4.icmp_echo_ignore_broadcasts /etc/sysctl.conf /etc/sysctl.d/* If " net.ipv4.icmp_echo_ignore_broadcasts" is not configured in the /etc/sysctl.conf file or in the /etc/sysctl.d/ directory, 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.

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

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