4.1.8 Configure firewall to drop all traffic

Information

firewalld should be set to deny all traffic by default.

A deny all policy is used to achieve a strong security posture by reducing attack surface by blocking any incoming or outgoing traffic not explicitly permitted.

Solution

Run the following to set the drop zone as the default.

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

Reload firewalld for changes to take effect

# firewall-cmd --reload

Impact:

Configuring firewalld to utilize a default policy of denying all traffic will effectively halt all communication not explicitly allowed.

Note: Configuration of a live systems firewall directly over a remote connection will often result in being locked out. It is advised to have a known good firewall configuration set to run on boot and to configure an entire firewall structure in a script that is then run and tested before saving to boot.

See Also

https://workbench.cisecurity.org/benchmarks/25279

Item Details

Category: SECURITY ASSESSMENT AND AUTHORIZATION, SYSTEM AND COMMUNICATIONS PROTECTION

References: 800-53|CA-9, 800-53|SC-7, 800-53|SC-7(5), CSCv7|9.4

Plugin: Unix

Control ID: 7d7f2255955e69767f5045d2c6f47221618df942892733bf66a9bbdceba30a9e