MantisBT before 1.2.18 does not properly check permissions when sending an email that indicates when a monitored issue is related to another issue, which allows remote authenticated users to obtain sensitive information about restricted issues.
https://www.mantisbt.org/bugs/view.php?id=9885
https://www.mantisbt.org/bugs/changelog_page.php?version_id=191
http://www.debian.org/security/2015/dsa-3120