A cross-site scripting (XSS) vulnerability in MantisBT before 2.1.1 allows remote attackers to inject arbitrary HTML or JavaScript (if MantisBT's CSP settings permit it) by modifying 'window_title' in the application configuration. This requires privileged access to MantisBT configuration management pages (i.e., administrator access rights) or altering the system configuration file (config_inc.php).
https://mantisbt.org/bugs/view.php?id=22266
http://github.com/mantisbt/mantisbt/commit/a85b0b96c8ebe3e010d0d016cf88ab3c8bfc196a