The flaw is triggered when apps that require a PIN to complete the authorization process instead of the using the OAuth protocol. The expert discovered that some permissions such as that to access direct messages, remained hidden to the Twitter user.
Terence Eden was awarded $2,940 for reporting the bug to Twitter under the bug bounty program operated through the HackerOne platform. According to Eden, the bug resides in the way the official Twitter API handles keys and secrets that could be accessed by app developers even without the service’s authorization.
“For some reason, Twitter’s OAuth screen says that these apps do not have access to Direct Messages. But they do!
In short, users could be tricked into allowing access to their DMs.”
Twitter implemented some restrictions, the most important one is restricting callback addresses. After successful login, the apps will only return to a predefined URL preventing the abuse of the official Twitter keys to send the user to your app.
The problem is that there are some apps that haven’t a URL or don’t support callbacks. For these apps, Twitter has implemented an alternative
In this alternative scenario, Eden discovered that apps did not show the correct OAuth details to the user, in particular, that the app was not able to access user direct messages.
Below the bug timeline:
(Security Affairs –Twitter, hacking)