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RHEL 8 must prevent Internet Control Message Protocol (ICMP) redirect messages from being accepted.


Overview

Finding ID Version Rule ID IA Controls Severity
V-230535 RHEL-08-040210 SV-230535r627750_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 modify the host's route table and are unauthenticated. An illicit ICMP redirect message could result in a man-in-the-middle attack.
STIG Date
Red Hat Enterprise Linux 8 Security Technical Implementation Guide 2021-03-04

Details

Check Text ( C-33204r568351_chk )
Verify RHEL 8 will not accept 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 default "accept_redirects" variables with the following command:

$ sudo sysctl net.ipv4.conf.default.accept_redirects net.ipv6.conf.default.accept_redirects

net.ipv4.conf.default.accept_redirects = 0
net.ipv6.conf.default.accept_redirects = 0

If the returned lines do not have a value of "0", or a line is not returned, this is a finding.
Fix Text (F-33179r568352_fix)
Configure RHEL 8 to prevent ICMP redirect messages from being accepted with the following command:

$ sudo sysctl -w net.ipv4.conf.default.accept_redirects=0

$ sudo sysctl -w net.ipv6.conf.default.accept_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.default.accept_redirects=0

net.ipv6.conf.default.accept_redirects=0