A flaw was found in the way that the Mantis BTS handled attachments and MIME types. A user could upload an HTML file renamed to a .gif and Mantis would calculate the actual MIME type of the file as text/html. A user tricked into thinking they were clicking a .gif attachment would instead have the full HTML file rendered in the browser, rather than having it treated as a downloadable file or displayed in plain text.

References:

http://www.mantisbt.org/bugs/view.php?id=11952 http://www.mantisbt.org/blog/?p=113

This was corrected in upstream version 1.2.2 and affects current Fedora 12, 13, rawhide, and EPEL5.