3.2.5 Ensure broadcast ICMP requests are ignored (Scored)

Level 1 - Server
Level 1 - Workstation 

Setting net.ipv4.icmp_echo_ignore_broadcasts to 1 will cause the system to ignore all ICMP echo and timestamp requests to broadcast and multicast addresses.

Accepting ICMP echo and timestamp requests with broadcast or multicast destinations for your network could be used to trick your host into starting (or participating) in a Smurf attack. A Smurf attack relies on an attacker sending large amounts of ICMP broadcast messages with a spoofed source address. All hosts receiving this message and responding would send echo-reply messages back to the spoofed address, which is probably not routable. If many hosts respond to the packets, the amount of traffic on the network could be significantly multiplied.

Run the following command and verify output matches:

# sysctl net.ipv4.icmp_echo_ignore_broadcasts 
net.ipv4.icmp_echo_ignore_broadcasts = 1

Set the following parameter in the /etc/sysctl.conf file:

net.ipv4.icmp_echo_ignore_broadcasts = 1

Run the following commands to set the active kernel parameters:

# sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=1 
# sysctl -w net.ipv4.route.flush=1