Title

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. (Cat II impact)

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

Additional Identifiers

Rule ID: SV-204613r880809_rule

Vulnerability ID: V-204613

Group Title: SRG-OS-000480-GPOS-00227

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.