A RHEL 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. RHEL 9 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.
- ID
- SV-257937r991589_rule
- Version
- RHEL-09-251020
- Severity
- Medium
- References
- Updated
Remediation Templates
A Manual Procedure
Configure the "firewalld" daemon to employ a deny-all, allow-by-exception with the following commands:
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