The "View Bugs" page (view_all_bug_page.php) in Mantis 0.17.4a and earlier includes summaries of private bugs for users that do not have access to any projects.
https://exchange.xforce.ibmcloud.com/vulnerabilities/9955
https://euvd.enisa.europa.eu/vulnerability/EUVD-2002-1104
http://www.securityfocus.com/bid/5565