MyBB 1.8.17 - Cross-Site Scripting

# Exploit Title: MyBB 1.8.17 - Cross-Site Scripting
# Date: 2018-08-11
# Author: 0xB9
# Twitter: @0xB9Sec
# Contact: 0xB9[at]pm.me
# Software Link: https://mybb.com/download/
# Version: 1.8.17
# Tested on: Ubuntu 18.04
# CVE: CVE-2018-15596

# 1. Description:
# On the forum RSS Syndication page you can generate a URL for example... 
# http://localhost/syndication.php?fid=&type=atom1.0&limit=15, the thread titles on 
# those generated links aren't sanitized. 
 
# 2. Proof of Concept:

- Make or find a thread of yours on the RSS feed
- Use this payload as the thread title  <a href="//google.com">Cool Thread Title</a>
- View RSS feed with your thread again but with the generated URL and click on your thread
- When the thread is clicked you will be redirected to google.com