fb_lock_mgr in Firebird 1.5 uses weak permissions (0666) for the semaphore array, which allows local users to cause a denial of service (blocked query processing) by locking semaphores.
http://www.securityfocus.com/bid/28474
http://www.firebirdsql.org/rlsnotes/Firebird-2.0-ReleaseNotes.pdf