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

From Canonical Ubuntu 16.04 Security Technical Implementation Guide

Associated with: CCI-000366

SV-90557r2_rule The Ubuntu 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 Internet Control Message Protocol (ICMP) echoes facilitates network mapping and provides a vector for amplification attacks.

Check content

Verify the Ubuntu operating system does not respond to IPv4 Internet Control Message Protocol (ICMP) echoes sent to a broadcast address. Check the value of the "icmp_echo_ignore_broadcasts" variable with the following command: # sudo sysctl 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

Configure the Ubuntu operating system to not respond to Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) echoes sent to a broadcast address with the following command: # sudo sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=1 If "1" is not the system's default value then add or update the following line in "/etc/sysctl.conf" or in the appropriate file under "/etc/sysctl.d": net.ipv4.icmp_echo_ignore_broadcasts=1

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