Facebook OAuth is used to communicate between Applications & Facebook users, to grant additional permissions to your favorite apps. To make this possible, users have to ” the application request so that app can access your account information with required permissions. Whitehat Hacker ‘Nir Goldshlager’ reported ‘The Hacker News’ that he discovered a very critical vulnerability in Facebook’s OAuth system, that allowed him to get full control over any Facebook account easily even without ‘allow or accept’ options.
Source: https://thehackernews.com/2013/02/facebook-oauth-flaw-allows-gaining-full.html