Title

The Red Hat Enterprise Linux operating system must not send Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirects. (Cat II impact)

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. # grep 'net.ipv4.conf.all.send_redirects' /etc/sysctl.conf /etc/sysctl.d/* If "net.ipv4.conf.all.send_redirects" 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 "0", this is a finding. Check that the operating system implements the "all send_redirects" variables with the following command: # /sbin/sysctl -a | grep 'net.ipv4.conf.all.send_redirects' net.ipv4.conf.all.send_redirects = 0 If the returned line does not have a value of "0", 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 a configuration file in the /etc/sysctl.d/ directory (or modify the line to have the required value): net.ipv4.conf.all.send_redirects = 0 Issue the following command to make the changes take effect: # sysctl --system

Additional Identifiers

Rule ID: SV-204617r603261_rule

Vulnerability ID: V-204617

Group Title: SRG-OS-000480-GPOS-00227

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.