MyBB Hide Thread Content Plugin 1.0 - Information Disclosure

# Exploit Title: MyBB Hide Thread Content Plugin 1.0 - Information Disclosure
# Date: 1/27/2021
# Author: 0xB9
# Twitter: @0xB9Sec
# Contact: 0xB9[at]pm.me
# Software Link: https://community.mybb.com/mods.php?action=view&pid=1430
# Version: 1.0
# Tested on: Windows 10
# CVE: CVE-2021-3337

1. Description:
This plugin hides thread content until user replies to the thread. The information disclosure is hidden content can be viewed without replying.

2. Proof of Concept:

- Visit a post where content is hidden
- Click the reply or quote button below
Thread content will be displayed in the [quote] bracket without needing to reply