Directory Services in Apple Mac OS X 10.5 through 10.5.4, when Active Directory is used, allows attackers to enumerate user names via wildcard characters in the Login Window.
https://exchange.xforce.ibmcloud.com/vulnerabilities/45163
http://www.vupen.com/english/advisories/2008/2584
http://www.us-cert.gov/cas/techalerts/TA08-260A.html
http://www.securityfocus.com/bid/31189
http://securitytracker.com/id?1020874
http://secunia.com/advisories/31882
http://lists.apple.com/archives/security-announce//2008/Sep/msg00005.html