When you open an XML document with Microsoft Internet Explorer, if the XML document is corrupted (for example, if the document is a truncated UNICODE XML document), Internet Explorer stops responding (hangs) and may crash.

To resolve this problem, obtain the latest service pack for Microsoft Data Access Components 2.6. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article. This problem was first corrected in Microsoft Data Access Components 2.6 Service Pack 2.

The following code uses the MSXML 3.0 parser to load an object that supports the IStream interface. This object only contains the first 3 bytes of an UNICODE XML document, so the XML document is truncated and data is corrupted. The XML parser fails to detect the corrupted data and loads it into a XML DOMDocument. The parser also fails to release the IStream interface properly when it processes the corrupted XML document, which eventually causes an access violation in some clients, such as Internet Explorer.

Steps to Reproduce Behavior

1. In Microsoft Visual C++, create a new Win32 Console project.
2. Add a new C++ file to the project and paste the following code into the C++ file:

   
   //Change msxml3.dll to msxml2.dll if Msxml2.dll is used.
   #import "msxml3.dll" 
   #include <stdio.h>
   
   class clsIStreamOnMemory : public IStream
   {
   private:
   	DWORD		m_dwRef;
   
   	char *		m_pcBuffer;
   	unsigned	m_uBufferSize;
   
   	unsigned	m_uFilePos;
   
   public:
   	clsIStreamOnMemory( void * pvBuffer, unsigned uSize )
   	: m_dwRef(0)
   	, m_pcBuffer( reinterpret_cast<char *>(pvBuffer) )
   	, m_uBufferSize(uSize)
   	, m_uFilePos(0)
   		{}
   
   	DWORD GetRefCount() const
   	{ return m_dwRef; }
   
   // IUnknown
               virtual HRESULT STDMETHODCALLTYPE QueryInterface( 
                   /* [in] */ REFIID riid,
                   /* [iid_is][out] */ void __RPC_FAR *__RPC_FAR *ppvObject);
               
               virtual ULONG STDMETHODCALLTYPE AddRef( void);
               
               virtual ULONG STDMETHODCALLTYPE Release( void);
   
   // ISequentialStream
           virtual /* [local] */ HRESULT STDMETHODCALLTYPE Read( 
               /* [length_is][size_is][out] */ void __RPC_FAR *pv,
               /* [in] */ ULONG cb,
               /* [out] */ ULONG __RPC_FAR *pcbRead);
           
           virtual /* [local] */ HRESULT STDMETHODCALLTYPE Write( 
               /* [size_is][in] */ const void __RPC_FAR *pv,
               /* [in] */ ULONG cb,
               /* [out] */ ULONG __RPC_FAR *pcbWritten)
   		{ 	// Not needed.
   			return E_NOTIMPL;
   		}
   
   // IStream
           virtual /* [local] */ HRESULT STDMETHODCALLTYPE Seek( 
               /* [in] */ LARGE_INTEGER dlibMove,
               /* [in] */ DWORD dwOrigin,
               /* [out] */ ULARGE_INTEGER __RPC_FAR *plibNewPosition)
   		{ 	// Not needed.
   			return E_NOTIMPL;
   		}
           
           virtual HRESULT STDMETHODCALLTYPE SetSize( 
               /* [in] */ ULARGE_INTEGER libNewSize)
   		{ 	// Not needed.
   			return E_NOTIMPL;
   		}
           
           virtual /* [local] */ HRESULT STDMETHODCALLTYPE CopyTo( 
               /* [unique][in] */ IStream __RPC_FAR *pstm,
               /* [in] */ ULARGE_INTEGER cb,
               /* [out] */ ULARGE_INTEGER __RPC_FAR *pcbRead,
               /* [out] */ ULARGE_INTEGER __RPC_FAR *pcbWritten)
   		{ 	// Not needed.
   			return E_NOTIMPL;
   		}
           
           virtual HRESULT STDMETHODCALLTYPE Commit( 
               /* [in] */ DWORD grfCommitFlags)
   		{ 	// Not needed.
   			return E_NOTIMPL;
   		}
       
           
           virtual HRESULT STDMETHODCALLTYPE Revert( void)
   		{ 	// Not needed.
   			return E_NOTIMPL;
   		}
           
           virtual HRESULT STDMETHODCALLTYPE LockRegion( 
               /* [in] */ ULARGE_INTEGER libOffset,
               /* [in] */ ULARGE_INTEGER cb,
               /* [in] */ DWORD dwLockType)
   		{ 	// Not needed.
   			return E_NOTIMPL;
   		}
           
           virtual HRESULT STDMETHODCALLTYPE UnlockRegion( 
               /* [in] */ ULARGE_INTEGER libOffset,
               /* [in] */ ULARGE_INTEGER cb,
               /* [in] */ DWORD dwLockType)
   		{ 	// Not needed.
   			return E_NOTIMPL;
   		}
   
           virtual HRESULT STDMETHODCALLTYPE Stat( 
               /* [out] */ STATSTG __RPC_FAR *pstatstg,
               /* [in] */ DWORD grfStatFlag)
   		{ 	// Not needed.
   			return E_NOTIMPL;
   		}
           
           virtual HRESULT STDMETHODCALLTYPE Clone( 
               /* [out] */ IStream __RPC_FAR *__RPC_FAR *ppstm)
   		{ 	// Not needed.
   			return E_NOTIMPL;
   		}
   
   };
   
   
   
   static void TestFailed();
   
   
   int main(int argc, char* argv[])
   {
   	CoInitialize(NULL);
   
   	TestFailed();
   
   	CoUninitialize();
   
   	return 0;
   }
   
   static void TestFailed()
   {
   	try
   	{
   		MSXML2::IXMLDOMDocumentPtr spDoc;
   		
   		//If MSXML2.dll is used, change FreeThreadedDOMDocument30 to FreeThreadedDOMDocument26.
   		HRESULT hr = spDoc.CreateInstance( __uuidof(MSXML2::FreeThreadedDOMDocument30) );
   		
   		if (hr != S_OK)
   		{
   			printf( "*** ERROR:failed to instantiate DOM document (hr = 0x%8.8x\n)", hr );
   			return;
   		}
   
   		/* This is the Unicode XML document that you are to load. */ 
   
   		WCHAR szDocument[] = { L"_<root></root>" };
   
   		//add the Unicode byte order mark to the beginning of the document. 
   		szDocument[0] = 0xFEFF;
   
   		// Create the corrupted document by truncating the document to 3 bytes. 
   		unsigned uBufferSize = 3;	
   
   		clsIStreamOnMemory isom( szDocument, uBufferSize );
   
   		VARIANT_BOOL bLoaded = spDoc->load( &isom );
   
   		if (isom.GetRefCount() != 0)
   		{
   			printf( "*** ERROR: document is holding onto IStream when it shouldn't.\n" );
   		}
   
   		if (bLoaded)
   		{
   			if (uBufferSize < 4)
   			{
   				printf( "*** ERROR: Parser loaded a corrupted document.\n" );
   			}
   			else
   			{
   				printf( "Document loaded OK\n" );
   			}
   		}
   		else
   		{
   			printf( "Document failed to load\n" );
   		}
   	}
   	catch (_com_error e)
   	{
   		_bstr_t bsDesc = e.Description();
   	}
   	getchar();
   }
   
   
   
   HRESULT STDMETHODCALLTYPE clsIStreamOnMemory::QueryInterface( 
                   /* [in] */ REFIID riid,
                   /* [iid_is][out] */ void __RPC_FAR *__RPC_FAR *ppvObject)
   {
   	if (   IsEqualIID( riid, __uuidof(IUnknown))
   		|| IsEqualIID( riid, __uuidof(IStream))
   		)
   	{
   		*ppvObject = reinterpret_cast<void *>(static_cast<IStream *>(this));
   		AddRef();
   		return S_OK;
   	}
   
   	return E_NOINTERFACE;
   }
               
   ULONG STDMETHODCALLTYPE clsIStreamOnMemory::AddRef( void)
   {
   	m_dwRef ++;
   	return m_dwRef;
   }
               
   ULONG STDMETHODCALLTYPE clsIStreamOnMemory::Release( void)
   {
   	m_dwRef --;
   	return m_dwRef;
   }
   
   // ISequentialStream
   HRESULT STDMETHODCALLTYPE clsIStreamOnMemory::Read( 
               /* [length_is][size_is][out] */ void __RPC_FAR *pv,
               /* [in] */ ULONG cb,
               /* [out] */ ULONG __RPC_FAR *pcbRead)
   {
   	if (m_uFilePos >= m_uBufferSize)
   	{
   		// Past end of file.
   		if (pcbRead != NULL)
   		{
   			*pcbRead = 0;
   		}
   		return S_OK;
   	}
   
   	if (cb > m_uBufferSize - m_uFilePos)
   	{
   		cb = m_uBufferSize - m_uFilePos;
   	}
   
   	const char * pszCur = &m_pcBuffer[m_uFilePos];
   	memcpy( pv, &m_pcBuffer[m_uFilePos], cb );
   	m_uFilePos += cb;
   
   	if (pcbRead != NULL)
   	{
   		*pcbRead = cb;
   	}
   
   	return S_OK;
   
   }
   					

3. Compile and run the project. In the console window, you can see the following output:
   *** ERROR: document is holding onto IStream when it shouldn't.
   *** ERROR: Parser loaded a corrupted document.