Stage 2: Removing Restrictions

Now that we have a window handle, we can send any messages we like to that control and it will blindly execute them. First things first - let's make sure we have enough space for our shellcode.

Within Shatter, type your window handle into the "Handle" box. The message to set the maximum text length of an edit box is EM_SETLIMITTEXT. The first parameter is the new maximum text length, and the second parameter is ignored. Type 4 into the WPARAM box, and 0 into the third. Click on EM_SETLIMITTEXT to send the message, and try to type something into the VirusScan edit box. You shouldn't be able to type more than 4 characters. Change the 4 to FFFFFFFF and send the message again. Now try typing into the VirusScan edit box; you now have over 4Gb (theoretically) of space within that edit control. Should be enough for even the most wasteful shellcode.

Stage 3: Injecting Shellcode


Next up, let's try pasting something into the box. Yes, OK, you could just right-click and choose Paste, but for the sake of argument let's work as if we couldn't do that. Clear the VirusScan edit box, and fire up Notepad. Type some text into Notepad, and copy it. Back in Shatter, we want to send VirusScan a "Paste clipboard contents" message, which is WM_PASTE. Both parameters for this message should be zero, so set the WPARAM and LPARAM to zero, leaving the handle the same. Click WM_PASTE, and watch your text appear in the VirusScan edit box. Click it again, and it should now be there twice. Fun, huh?

OK, that's enough playing. Clear the VirusScan edit box again, and fire up your hex editor. Load up sploit.bin, included in the Shatter zipfile. This is the shellcode taken from Jill (Hey, Dark Spyrit!) which fires a remote command shell back to you. It's hard-coded to send a command shell to the loopback adress on port 123, so now's probably a good time to fire up a Netcat listener before you forget. Fire up a cmd, hit "nc -lp 123" and forget it. Back to our hex edit. Copy the shellcode to the clipboard, making sure you get all of it (including the FOON at the beginning - we'll need that in a sec). Back to Shatter, and hit the WM_PASTE button again. You should now see a whole load of nasty-looking characters in the VirusScan edit box; that's our shellcode, nicely pasted in.

Stage 4: Executing the code