STIG ID: RHEL-07-040660 | SRG: SRG-OS-000480-GPOS-00227 | Severity: medium | CCI: | Vulnerability Id: V-204617
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.
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
Verify the system does not send IPv4 ICMP redirect messages.
# grep -r net.ipv4.conf.all.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.all.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 "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.
If conflicting results are returned, this is a finding.