How to configure your Firewall on ClearOS

Unless you are using ClearOS as a Gateway, you should set the Network -> Settings -> IP Settings -> Network Mode to "Standalone" (https://example:81/app/network). This blocks everything.

Then visit https://example.org:81/app/incoming_firewall or via the admin panel Network -> Firewall -> Incoming where you can add some "Allowed Incoming Connections"

For example, if you are running a website, you should allow HTTP (port 80) and HTTPS (port 443):