Information
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 10 incorporates the "firewalld" daemon, which allows for many different configurations. One of these configurations is zones. Zones can be used in 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.
Solution
Configure RHEL 10 so that the "firewalld" daemon employs a deny-all, allow-by-exception policy with the following commands (using ens133 as an example interface):
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:
$ sudo firewall-cmd --permanent --add-service=ssh --zone=drop
Reload the firewall rules to update the runtime configuration from the "--permanent" changes made above:
$ sudo firewall-cmd --reload
Set the default zone to the drop zone:
$ sudo firewall-cmd --set-default-zone=drop
Note: This is a runtime and permanent change.
Add any interfaces to the newly modified "drop" zone:
$ sudo firewall-cmd --permanent --zone=drop --change-interface=ens33
Reload the firewall rules for changes to take effect:
$ sudo firewall-cmd --reload