RHEL 8 must not send Internet Control Message Protocol (ICMP) redirects.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-230536	RHEL-08-040220	SV-230536r599732_rule		Medium

Description
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. There are notable differences between Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6). There is only a directive to disable sending of IPv4 redirected packets. Refer to RFC4294 for an explanation of "IPv6 Node Requirements", which resulted in this difference between IPv4 and IPv6.

Description

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. There are notable differences between Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6). There is only a directive to disable sending of IPv4 redirected packets. Refer to RFC4294 for an explanation of "IPv6 Node Requirements", which resulted in this difference between IPv4 and IPv6.

STIG	Date
Red Hat Enterprise Linux 8 Security Technical Implementation Guide	2020-11-25

Details

Check Text ( C-33205r568354_chk )
Verify RHEL 8 does not IPv4 ICMP redirect messages. Note: If either IPv4 or IPv6 is disabled on the system, this requirement only applies to the active internet protocol version. Check the value of the "all send_redirects" variables with the following command: $ sudo sysctl net.ipv4.conf.all.send_redirects 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.

Check Text ( C-33205r568354_chk )

Verify RHEL 8 does not IPv4 ICMP redirect messages.

Note: If either IPv4 or IPv6 is disabled on the system, this requirement only applies to the active internet protocol version.

Check the value of the "all send_redirects" variables with the following command:

$ sudo sysctl net.ipv4.conf.all.send_redirects

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 (F-33180r568355_fix)
Configure RHEL 8 to not allow interfaces to perform IPv4 ICMP redirects with the following command: $ sudo sysctl -w net.ipv4.conf.all.send_redirects=0 If "0" is not the system's default value then add or update the following line in the appropriate file under "/etc/sysctl.d": net.ipv4.conf.all.send_redirects=0