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.\