Multiple unspecified vulnerabilities in Firebird 1.5 allow remote attackers to (1) cause a denial of service (application crash) by sending many remote protocol versions; and (2) cause a denial of service (connection drop) via certain network traffic, as demonstrated by Nessus vulnerability scanning.
http://www.securityfocus.com/bid/28474
http://www.firebirdsql.org/rlsnotes/Firebird-2.0-ReleaseNotes.pdf