An issue was discovered in MantisBT before 2.24.5. It associates a unique cookie string with each user. This string is not reset upon logout (i.e., the user session is still considered valid and active), allowing an attacker who somehow gained access to a user's cookie to login as them.
core/email_api.php in MantisBT before 1.2.12 does not properly manage the sending of e-mail notifications about restricted bugs, which might allow remote authenticated users to obtain sensitive information by adding a note to a bug before losing permission to view that bug.