Ensure ufw Default Deny Firewall Policy

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Description

A default deny policy on connections ensures that any unconfigured network usage will be rejected.

Note: Any port or protocol without a explicit allow before the default deny will be blocked.

Rationale

With a default accept policy the firewall will accept any packet that is not configured to be denied. It is easier to allow acceptable usage than to block unacceptable usage.

Warning

Changing firewall settings while connected over network can result in being locked out of the system.