The "Project Documentation" feature in MantisBT 1.2.19 and earlier, when the threshold to access files ($g_view_proj_doc_threshold) is set to ANYBODY, allows remote authenticated users to download attachments linked to arbitrary private projects via a file id number in the file_id parameter to file_download.php.
https://github.com/mantisbt/mantisbt/commit/f39cf5251953b468e9d921e1cf2aca3abdb00772
https://github.com/mantisbt/mantisbt/commit/a4be76d6e5c4939545d84712c79d3f8f4a108c4f
https://bugzilla.redhat.com/show_bug.cgi?id=1237199
http://www.securityfocus.com/bid/75414
http://www.openwall.com/lists/oss-security/2015/06/25/4
http://www.openwall.com/lists/oss-security/2015/06/25/3
http://lists.fedoraproject.org/pipermail/package-announce/2015-August/163191.html