Question

I have a Win32 application that gets the HANDLE of a MFC application. My goal is to force the MFC program not to display ASSERT error message box.

Basically, I have made a prototype that allows my Win32 application to force the MFC application to show a message box, just to check if the idea is possible. Now I need to force the MFC application not to display such ASSERT error message boxes.

Is that possible?

Answer 1

You can do this by intercepting the MessageBoxA/MessageBoxW function call. At a usermode level, this is typically done in one of three places:

• Call site – There may be more than one call to MessageBox in your executable. You need to find the one that you want to disable. Then you can overwrite the call with code that does nothing (i.e. overwrite with nop instructions).
• IAT – The Import Address Table; a table of function pointers filled in by the PE loader. Execution often (but not always) flows through here and replacing the function pointer for MessageBox can allow the MessageBox call to be redirected to some routine that does nothing.
• Function entry point – The start of the MessageBox function. This can be located by GetProcAddress and the first instruction replaced with a ret.

The manipulation is done either at runtime (dynamically) or statically (binary rewriting/executable editing) with the first option being far more common. A library which can help you achieve runtime detouring is Microsoft Detours.

This is not a comprehensive list of all the possibilities, but rather the most common methods of execution redirection and detouring.