Modifying a program to fake a button press

Question

I have an MFC application that I was given (without source code) which opens a window with an 'Update' button, which then performs a very long update after being clicked.

I'd like to modify the program so that when the window is created (or somewhere else such as DoModal), a message is sent to the program to make it think that the button was pressed.

I've been toying around with this for a while in Ida Pro and OllyDbg to no avail. I looked at possibly using PumpMessage, but this did not bring any success.

Any advice?

Answer 1

If you don't like the idea of using a secondary "macro" program, you could patch the original program's binary to call the button's BM_CLICK handler. If you can find some space for the call (minimum 5 bytes without arguments), you can do this with OllyDbg alone (after editing the code, select it, and select "Copy to executable" -> "Selection" from the right-click menu). Otherwise, you'll need to create a new code section with a PE editor (e.g. LordPE or PE Tools) and add your code there (typically you'll want to change a call in the program to a jump to your section, where you perform the original call plus the call to the button's click handler, then jump back to the old position after your patched jump).