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A RHEL 8 firewall must employ a deny-all, allow-by-exception policy for allowing connections to other systems.


Overview

Finding ID Version Rule ID IA Controls Severity
V-230504 RHEL-08-040090 SV-230504r809321_rule Medium
Description
Failure to restrict network connectivity only to authorized systems permits inbound connections from malicious systems. It also permits outbound connections that may facilitate exfiltration of DoD data. RHEL 8 incorporates the "firewalld" daemon, which allows for many different configurations. One of these configurations is zones. Zones can be utilized to a deny-all, allow-by-exception approach. The default "drop" zone will drop all incoming network packets unless it is explicitly allowed by the configuration file or is related to an outgoing network connection.
STIG Date
Red Hat Enterprise Linux 8 Security Technical Implementation Guide 2022-06-15

Details

Check Text ( C-33173r568258_chk )
Verify "firewalld" is configured to employ a deny-all, allow-by-exception policy for allowing connections to other systems with the following commands:

$ sudo firewall-cmd --state

running

$ sudo firewall-cmd --get-active-zones

[custom]
interfaces: ens33

$ sudo firewall-cmd --info-zone=[custom] | grep target

target: DROP

If no zones are active on the RHEL 8 interfaces or if the target is set to a different option other than "DROP", this is a finding.
Fix Text (F-33148r809320_fix)
Configure the "firewalld" daemon to employ a deny-all, allow-by-exception with the following commands:

$ sudo firewall-cmd --permanent --new-zone=[custom]

$ sudo cp /usr/lib/firewalld/zones/drop.xml /etc/firewalld/zones/[custom].xml

This will provide a clean configuration file to work with that employs a deny-all approach. Note: Add the exceptions that are required for mission functionality and update the short title in the xml file to match the [custom] zone name.

Reload the firewall rules to make the new [custom] zone available to load:
$ sudo firewall-cmd --reload

Set the default zone to the new [custom] zone:
$ sudo firewall-cmd --set-default-zone=[custom]

Note: This is a runtime and permanent change.
Add any interfaces to the new [custom] zone:
$ sudo firewall-cmd --permanent --zone=[custom] --change-interface=ens33

Reload the firewall rules for changes to take effect:
$ sudo firewall-cmd --reload