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The system must not respond to ICMPv4 sent to a broadcast address.


Finding ID Version Rule ID IA Controls Severity
V-217921 RHEL-06-000092 SV-217921r505923_rule Low
Ignoring ICMP echo requests (pings) sent to broadcast or multicast addresses makes the system slightly more difficult to enumerate on the network.
Red Hat Enterprise Linux 6 Security Technical Implementation Guide 2020-09-03


Check Text ( C-19402r376778_chk )
The status of the "net.ipv4.icmp_echo_ignore_broadcasts" kernel parameter can be queried by running the following command:

$ sysctl net.ipv4.icmp_echo_ignore_broadcasts
net.ipv4.icmp_echo_ignore_broadcasts = 1

$ grep net.ipv4.icmp_echo_ignore_broadcasts /etc/sysctl.conf /etc/sysctl.d/*
net.ipv4.icmp_echo_ignore_broadcasts = 1

If "net.ipv4.icmp_echo_ignore_broadcasts" is not configured in the /etc/sysctl.conf file or in the /etc/sysctl.d/ directory, is commented out or does not have a value of "1", this is a finding.
Fix Text (F-19400r376779_fix)
To set the runtime status of the "net.ipv4.icmp_echo_ignore_broadcasts" kernel parameter, run the following command:

# sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=1

Set the system to the required kernel parameter by adding the following line to "/etc/sysctl.conf" or a config file in the /etc/sysctl.d/ directory (or modify the line to have the required value):

net.ipv4.icmp_echo_ignore_broadcasts = 1

Issue the following command to make the changes take effect:

# sysctl --system