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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-38535 RHEL-06-000092 SV-50336r2_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 2015-05-26


Check Text ( C-46093r2_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

The output of the command should indicate a value of "1". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf".

$ grep net.ipv4.icmp_echo_ignore_broadcasts /etc/sysctl.conf

If the correct value is not returned, this is a finding.
Fix Text (F-43483r1_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

If this is not the system's default value, add the following line to "/etc/sysctl.conf":

net.ipv4.icmp_echo_ignore_broadcasts = 1