After registration, but before account activation, there is a possibility to perform forum-related actions (like subscribe to threads for example).
Steps to reproduce:
- Click on an image in a forum post when not logged in
- Open a new tab, register yourself with some username and e-mail address, click on Confirm registration
- In your inbox you'll find an e-mail containing the activation link
- But before clicking the link, the images can be viewed, or, for example, I can subscribe to a forum thread.
Seems one can perform privileged forum actions before the account is verified...
(Only tested it with viewing post images and subscribing to a forum thread.)