The check_scramble_323 function in MySQL 4.1.x before 4.1.3, and 5.0, allows remote attackers to bypass authentication via a zero-length scrambled string.
http://www.kb.cert.org/vuls/id/184030
http://marc.info/?l=bugtraq&m=108904917528205&w=2
http://archives.neohapsis.com/archives/vulnwatch/2004-q3/0001.html