An XSS issue was discovered in admin/install.php in MantisBT before 1.3.12 and 2.x before 2.5.2. Some variables under user control in the MantisBT installation script are not properly sanitized before being output, allowing remote attackers to inject arbitrary JavaScript code, as demonstrated by the $f_database, $f_db_username, and $f_admin_username variables. This is mitigated by the fact that the admin/ folder should be deleted after installation, and also prevented by CSP.
https://mantisbt.org/bugs/view.php?id=23146
https://github.com/mantisbt/mantisbt/commit/c73ae3d3d4dd4681489a9e697e8ade785e27cba5
https://github.com/mantisbt/mantisbt/commit/17f9b94f031ba93ae2a727bca0e68458ecd08fb0
http://www.securitytracker.com/id/1039030