The Active Template Library (ATL) in Microsoft Visual Studio .NET 2003 SP1, Visual Studio 2005 SP1 and 2008 Gold, and Visual C++ 2005 SP1 and 2008 Gold and SP1; and Windows 2000 SP4, XP SP2 and SP3, Server 2003 SP2, Vista Gold, SP1, and SP2, and Server 2008 Gold and SP2; does not prevent VariantClear calls on an uninitialized VARIANT, which allows remote attackers to execute arbitrary code via a malformed stream to an ATL (1) component or (2) control, related to ATL headers and error handling, aka "ATL Uninitialized Object Vulnerability."