3.5.1.7 Ensure unnecessary services and ports are not accepted

Information

Services and ports can be accepted or explicitly rejected or dropped by a zone.

For every zone, you can set a default behavior that handles incoming traffic that is not further specified. Such behavior is defined by setting the target of the zone. There are three options - default, ACCEPT, REJECT, and DROP.

ACCEPT - you accept all incoming packets except those disabled by a specific rule.

REJECT - you disable all incoming packets except those that you have allowed in specific rules and the source machine is informed about the rejection.

DROP - you disable all incoming packets except those that you have allowed in specific rules and no information sent to the source machine.

Rationale:

To reduce the attack surface of a system, all services and ports should be blocked unless required

Solution

Run the following command to remove an unnecessary service:

# firewall-cmd --remove-service=<service>

Example:

# firewall-cmd --remove-service=cockpit

Run the following command to remove an unnecessary port:

# firewall-cmd --remove-port=<port-number>/<port-type>

Example:

# firewall-cmd --remove-port=25/tcp

Run the following command to make new settings persistent:

# firewall-cmd --runtime-to-permanent

See Also

https://workbench.cisecurity.org/files/2925

Item Details

Category: SYSTEM AND COMMUNICATIONS PROTECTION

References: 800-53|SC-7(12), CSCv7|9.4

Plugin: Unix

Control ID: 88df808f67af1e7611443b93471418cf4fb4cf86746ff12d797369d8f13a55fd