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V-221881

CAT II (Medium)

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

Rule ID

SV-221881r991589_rule

STIG

Oracle Linux 7 Security Technical Implementation Guide

Version

V3R5

CCIs

CCI-000366

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 -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.

Fix Text

Configure the system not to 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