The system must not send Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirects.

From Red Hat Enterprise Linux 7 Security Technical Implementation Guide

Associated with: CCI-000366

SV-86917r2_rule The system must not send Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirects.

Vulnerability discussion

ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages contain information from the system's route table, possibly revealing portions of the network topology.

Check content

Verify the system does not send IPv4 ICMP redirect messages. Check the value of the "all send_redirects" variables with the following command: # grep 'net.ipv4.conf.all.send_redirects' /etc/sysctl.conf net.ipv4.conf.all.send_redirects=0 If the returned line does not have a value of "0", or a line is not returned, this is a finding.

Fix text

Configure the system to not allow interfaces to perform IPv4 ICMP redirects. Set the system to the required kernel parameter by adding the following line to "/etc/sysctl.conf" (or modify the line to have the required value): net.ipv4.conf.all.send_redirects=0

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