The Hide-Thread-Content plugin through 2021-01-27 for MyBB allows remote attackers to bypass intended content-reading restrictions by clicking on reply or quote in the postbit.
https://github.com/snlbaral/Hide-Thread-Content/issues/1
http://packetstormsecurity.com/files/161185/MyBB-Hide-Thread-Content-1.0-Information-Disclosure.html