net.ipv4.icmp_echo_ignore_broadcasts=1

3.3.5 Ensure broadcast ICMP requests are ignored - ‘net.ipv4.icmp_echo_ignore_broadcasts = 0’

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Information

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.

Solution

Set the following parameters in /etc/sysctl.conf or a /etc/sysctl.d/* file:
Example:

# printf ‘
net.ipv4.icmp_echo_ignore_broadcasts = 1
‘ » /etc/sysctl.d/60-netipv4_sysctl.conf

Run the following command to set the active kernel parameters:

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

Additional Information:

NIST SP 800-53 Rev. 5:

CM-1

CM-2

CM-6

CM-7

IA-5

See Also

https://workbench.cisecurity.org/files/3807

Item Details

Audit Name: CIS Rocky Linux 8 Server L1 v1.0.0

References: [CSCv7 9.2](https://www.tenable.com/audits/references/CSCv7/9.2)

Plugin: Unix

Control ID: 25c0e2bb7fa75bdf475547c9de72f77e9553087b409bdecc5026d28665c45f96

Updated: