AlmaLinux OS 9 firewall must employ a deny-all, allow-by-exception policy for allowing connections to other systems.

An XCCDF Rule

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. AlmaLinux OS 9 incorporates the "firewalld" daemon, which allows for many different configurations. One of these configurations is zones. Zones can be used 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.

ID: SV-269246r1050780_rule
Version: ALMA-09-018830
Severity: Medium
References: CCI-000366
Updated: about 2 months ago

Remediation Templates

Configure the "firewalld" daemon to employ a deny-all, allow-by-exception.

Start by adding the exceptions that are required for mission functionality to the "drop" zone. If SSH access on port 22 is needed for example, run the following command:

$ firewall-cmd --permanent --add-service=ssh --zone=drop
Set the default zone to the "drop" zone:

$ firewall-cmd --set-default-zone=drop

Note: This is a runtime and a permanent change.

Add any interfaces to the newly modified "drop" zone:

$ firewall-cmd --permanent --zone=drop --change-interface=enp1s0

Reload the firewall rules for changes to take effect:

$ firewall-cmd --reload

Check zones and interfaces:

$ firewall-cmd --get-active-zones

drop
  interfaces: enp1s0

Check new default zone's target is set to "DROP":

$ firewall-cmd --permanent --info-zone=drop | grep target

  target: DROP

The same outcome is achieved by creating a new zone, for example:

$ firewall-cmd --permanent --new-zone=stig
$ firewall-cmd --reload
$ firewall-cmd --permanent --change-interface=enp1s0 --zone=stig 
$ firewall-cmd --permanent --add-service=ssh --zone=stig
$ firewall-cmd --permanent --set-target=DROP --zone=stig
$ firewall-cmd --set-default-zone=stig

AlmaLinux OS 9 firewall must employ a deny-all, allow-by-exception policy for allowing connections to other systems.

Description

Remediation Templates

A Manual Procedure