Mantis before 1.1.3 does not unset the session cookie during logout, which makes it easier for remote attackers to hijack sessions.
https://exchange.xforce.ibmcloud.com/vulnerabilities/46084
http://www.openwall.com/lists/oss-security/2008/10/20/1
http://www.mantisbt.org/bugs/view.php?id=9664
http://www.mantisbt.org/bugs/file_download.php?file_id=1988&type=bug
http://www.mantisbt.org/bugs/changelog_page.php