The Export User plugin through 2.0 for MyBB allows XSS during the process of an admin generating DSGVO data for a user, via the Custom User Title, Location, or Bio field. NOTE: This vulnerability only affects products that are no longer supported by the maintainer.
https://community.mybb.com/user-121250.html
https://community.mybb.com/mods.php?action=view&pid=1408
http://packetstormsecurity.com/files/171421/MyBB-Export-User-2.0-Cross-Site-Scripting.html