The system must not respond to ICMPv4 sent to a broadcast address.

From Red Hat Enterprise Linux 6 Security Technical Implementation Guide

Associated with: CCI-000366

SV-50336r2_rule The system must not respond to ICMPv4 sent to a broadcast address.

Vulnerability discussion

Ignoring ICMP echo requests (pings) sent to broadcast or multicast addresses makes the system slightly more difficult to enumerate on the network.

Check content

The status of the "net.ipv4.icmp_echo_ignore_broadcasts" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.icmp_echo_ignore_broadcasts The output of the command should indicate a value of "1". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". $ grep net.ipv4.icmp_echo_ignore_broadcasts /etc/sysctl.conf If the correct value is not returned, this is a finding.

Fix text

To set the runtime status of the "net.ipv4.icmp_echo_ignore_broadcasts" kernel parameter, run the following command: # sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=1 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.icmp_echo_ignore_broadcasts = 1

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