You are not required to have a special rank to modify or create pages but, in order to contribute you do need a wiki account. If you don't have an account, you can create an account. If you already have an account, you can login and freely edit a page. This is brought in place to encourage more activity from normal users and also to gather information known only by one user per se.
Still, the Hack Forums Wiki is carefully moderated. Because of this, the ability to freely edit articles is moderated before publicly displaying the edit. This is to prevent any form of abuse inflicted on any page. Nevertheless, you can contribute without any fear of needing permission or special rank.