CVE-2000-0543
The command port for PGP Certificate Server 2.5.0 and 2.5.1 allows remote attackers to cause a denial of service if their hostname does not have a reverse DNS entry and they connect to port 4000.
Date published : 2000-07-12
http://www.securityfocus.com/bid/1343
http://archives.neohapsis.com/archives/bugtraq/2000-06/0107.html