MantisBT before 1.2.18 allows remote authenticated users to bypass the $g_download_attachments_threshold and $g_view_attachments_threshold restrictions and read attachments for private projects by leveraging access to a project that does not restrict access to attachments and a request to the download URL.
seclists.org/oss-sec/2014/q4/693
secunia.com/advisories/62101
www.debian.org/security/2015/dsa-3120
www.mantisbt.org/bugs/view.php?id=17742
www.openwall.com/lists/oss-security/2014/11/15/6
www.securityfocus.com/bid/71104
exchange.xforce.ibmcloud.com/vulnerabilities/98731
github.com/mantisbt/mantisbt/commit/5f0b150b