Title

The Red Hat Enterprise Linux operating system must not allow interfaces to perform Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirects by default. (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 allow interfaces to perform IPv4 ICMP redirects by default. # grep -r net.ipv4.conf.default.send_redirects /run/sysctl.d/* /etc/sysctl.d/* /usr/local/lib/sysctl.d/* /usr/lib/sysctl.d/* /lib/sysctl.d/* /etc/sysctl.conf 2> /dev/null If "net.ipv4.conf.default.send_redirects" is not configured in the "/etc/sysctl.conf" file or in any of the other sysctl.d directories, is commented out or does not have a value of "0", this is a finding. Check that the operating system implements the "default send_redirects" variables with the following command: # /sbin/sysctl -a | grep net.ipv4.conf.default.send_redirects net.ipv4.conf.default.send_redirects = 0 If the returned line does not have a value of "0", this is a finding. If conflicting results are returned, this is a finding.

Fix Text

Configure the system to not allow interfaces to perform IPv4 ICMP redirects by default. 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.default.send_redirects = 0 Issue the following command to make the changes take effect: # sysctl --system

Additional Identifiers

Rule ID: SV-204616r991589_rule

Vulnerability ID: V-204616

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

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