I've an ActiveX Control within an embedded IE8 HTML page that has the following event MessageReceived([in] BSTR srcWindowId, [in] BSTR json). On Windows the event is registered with OCX.attachEvent("MessageReceived", onMessageReceivedFunc).

Following code fires the event in the HTML page.

 HRESULT Fire_MessageReceived(BSTR id, BSTR json)
 {
  CComVariant varResult;
  T* pT = static_cast<T*>(this);
  int nConnectionIndex;
  CComVariant* pvars = new CComVariant[2];  
  int nConnections = m_vec.GetSize();
  for (nConnectionIndex = 0; nConnectionIndex < nConnections; nConnectionIndex++)
  {
   pT->Lock();
   CComPtr<IUnknown> sp = m_vec.GetAt(nConnectionIndex);
   pT->Unlock();
   IDispatch* pDispatch = reinterpret_cast<IDispatch*>(sp.p);
   if (pDispatch != NULL)
   {
    VariantClear(&varResult);

    pvars[1] = id;
    pvars[0] = json;

    DISPPARAMS disp = { pvars, NULL, 2, 0 };
    pDispatch->Invoke(0x1, IID_NULL, LOCALE_USER_DEFAULT, DISPATCH_METHOD, &disp, &varResult, NULL, NULL);
   }
  }
  delete[] pvars; // -> Memory Corruption here!
  return varResult.scode;
 }

After I enabled gflags.exe with application verifier, the following strange behaviour occur: After Invoke() that is executing the JavaScript callback, the BSTR from pvars[1] is copied to pvars[0] for some unknown reason!? The delete[] of pvars causes a double free of the same string then which ends in a heap corruption.

Does anybody has an idea whats going on here? Is this a IE bug or is there a trick within the OCX Implementation that I'm missing?

If I use the tag like:

<script for="OCX" event="MessageReceived(id, json)" language="JavaScript" type="text/javascript">
    window.onMessageReceivedFunc(windowId, json);
</script>

... the strange copy operation does not occur.

The following code also seem to be ok due to the fact that the caller of Fire_MessageReceived() is responsible for freeing the BSTRs.

HRESULT Fire_MessageReceived(BSTR srcWindowId, BSTR json)
 {
  CComVariant varResult;
  T* pT = static_cast<T*>(this);
  int nConnectionIndex;  
  VARIANT pvars[2];  
  int nConnections = m_vec.GetSize();
  for (nConnectionIndex = 0; nConnectionIndex < nConnections; nConnectionIndex++)
  {
   pT->Lock();
   CComPtr<IUnknown> sp = m_vec.GetAt(nConnectionIndex);
   pT->Unlock();
   IDispatch* pDispatch = reinterpret_cast<IDispatch*>(sp.p);
   if (pDispatch != NULL)
   {
    VariantClear(&varResult);

    pvars[1].vt = VT_BSTR;
    pvars[1].bstrVal = srcWindowId;
    pvars[0].vt = VT_BSTR;
    pvars[0].bstrVal = json;

    DISPPARAMS disp = { pvars, NULL, 2, 0 };
    pDispatch->Invoke(0x1, IID_NULL, LOCALE_USER_DEFAULT, DISPATCH_METHOD, &disp, &varResult, NULL, NULL);
   }
  }
  delete[] pvars;
  return varResult.scode;
 }

Thanks!