cyberstrikeus 3.2.5 Ensure broadcast ICMP requests are ignored (Scored)
Profile Applicability
- Level 1 - Server
- Level 1 - Workstation
Description
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.
Rationale
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.
Audit Procedure
Run the following commands and verify output matches:
sysctl net.ipv4.icmp_echo_ignore_broadcasts
# Expected: net.ipv4.icmp_echo_ignore_broadcasts = 1
grep "net\.ipv4\.icmp_echo_ignore_broadcasts" /etc/sysctl.conf /etc/sysctl.d/*
# Expected: net.ipv4.icmp_echo_ignore_broadcasts = 1
Expected Result
net.ipv4.icmp_echo_ignore_broadcasts = 1
Remediation
Set the following parameter in /etc/sysctl.conf or a /etc/sysctl.d/* 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
Default Value
Not specified.
References
- CIS Controls: 3 - Secure Configurations for Hardware and Software on Mobile Devices, Laptops, Workstations, and Servers
- CIS Controls: 11 - Secure Configurations for Network Devices such as Firewalls, Routers and switches
Profile
- Level 1 - Server
- Level 1 - Workstation