The system must not respond to Internet Control Message Protocol v4 (ICMPv4) echoes sent to a broadcast address.

From Red Hat Enterprise Linux 5 Security Technical Implementation Guide

Part of GEN003603

Associated with IA controls: ECSC-1

Associated with: CCI-001551

SV-37608r1_rule The system must not respond to Internet Control Message Protocol v4 (ICMPv4) echoes sent to a broadcast address.

Vulnerability discussion

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

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Fix text

Configure the system to not respond to ICMP ECHO_REQUESTs sent to broadcast addresses. Edit /etc/sysctl.conf and add a setting for "net.ipv4.icmp_echo_ignore_broadcasts=1" and reload the sysctls. Procedure: # echo "net.ipv4.icmp_echo_ignore_broadcasts=1" >> /etc/sysctl.conf # sysctl -p

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