MantisBT before 1.3.1 and 2.x before 2.0.0-beta.2 uses a weak Content Security Policy when using the Gravatar plugin, which allows remote attackers to conduct cross-site scripting (XSS) attacks via unspecified vectors.
https://mantisbt.org/bugs/view.php?id=21263
https://github.com/mantisbt/mantisbt/commit/b3511d2f