MantisBT before 1.2.11 does not check the delete_attachments_threshold permission when form_security_validation is set to OFF, which allows remote authenticated users with certain privileges to bypass intended access restrictions and delete arbitrary attachments.
https://github.com/mantisbt/mantisbt/commit/ceafe6f0c679411b81368052633a63dd3ca06d9c
http://www.securityfocus.com/bid/53921
http://www.openwall.com/lists/oss-security/2012/06/11/6
http://www.openwall.com/lists/oss-security/2012/06/09/1
http://www.mantisbt.org/bugs/view.php?id=14016
http://www.mantisbt.org/bugs/changelog_page.php?version_id=148
http://security.gentoo.org/glsa/glsa-201211-01.xml
http://secunia.com/advisories/51199
http://lists.fedoraproject.org/pipermail/package-announce/2012-November/093064.html
http://lists.fedoraproject.org/pipermail/package-announce/2012-November/093063.html
http://lists.fedoraproject.org/pipermail/package-announce/2012-November/092926.html