The LDAP server in Active Directory in Microsoft Windows 2000 SP4 and Server 2003 SP1 and SP2 responds differently to a failed bind attempt depending on…

The LDAP server in Active Directory in Microsoft Windows 2000 SP4 and Server 2003 SP1 and SP2 responds differently to a failed bind attempt depending on whether the user account exists and is permitted to login, which allows remote attackers to enumerate valid usernames via a series of LDAP bind requests, as demonstrated by ldapuserenum.