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 properly validate the share and servername fields in SMB packets, which allows remote attackers to cause a denial of service (system hang) via a crafted packet, aka "SMB Null Pointer Vulnerability."