The SMB implementation in the Server service in Microsoft Windows 2000 SP4, Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista Gold, SP1, and SP2, Windows Server 2008 Gold, SP2, and R2, and Windows 7 does not use a sufficient source of entropy, which allows remote attackers to obtain access to files and other SMB resources via a large number of authentication requests, related to server-generated challenges, certain "duplicate values," and spoofing of an authentication token, aka "SMB NTLM Authentication Lack of Entropy Vulnerability."