Currently I'm trying to get past Enigma's loader, which asks you for a name & key, as an excercise.

I have very little progress, as I haven't worked too much with packers.

What I did was breakpoint on CreateWindowExA, and then I put random data at key / name, and then click Register, which effectively breaks at CreateWindowExA.

From there, I'm able to check the stack and go back a few calls, but I'm really lost as there's a lot of bloat code (short functions with x87 instructions), and I don't know where to continue.

I also know that the routine that checks the serial is virtualized, so I should patch the places which check the return of the function that checks the serial instead of the function itself, but then again, I get lost when looking at the stack.

Here's my progress so far:

The breakpoint on CreateWindowExA, which gets called when you input an invalid serial enter image description here

The function that calls it: http://screenshotuploader.com/i/1502/t_q0c.png

And that function, before and after calling CreateWindowExA, calls these two weird x87 functions:

enter image description here

the function that is marked in the previous screenshot

enter image description here

this one gets called a few instructions after CreateWindowExA

After going one more function back, I see:

enter image description here

The problem with that function is that it's using some tricks to change the return address (I guess), like this:

enter image description here

Which then leads to weird code which expects a function pointer in edx returned by a funtion that is dereferencing a pointer to a word (2 bytes)!

Here's the code that calls the function that returns a pointer to a function: enter image description here

And here's the function that returns a pointer in edx: enter image description here

It is really weird, as it 1) derefs a word (2 bytes, not enough for a function pointer!), and 2) FLDCW loads a x87 FPU control word... what's happening here?!

Also, that's the last return I can see in the stack, as the rest of the values are zeroed, and there's no branch which checks the serial at this depth, so I don't know where to continue looking at.

And if not enough, the program closes each time I input an invalid serial, which makes it harder, because the next time the offsets are totally different and I can't find the code so I breakpoint a bit before, so I'm really lost!

Dumping the executable at runtime does absolutely nothing, as it's still packed as it was before, it just makes it 4x bigger (50MB -> 200MB), and doesn't help at all.

Any help would be great, even a simple idea, like a hint on what to do next, where to breakpoint, where to look at, or whatever you can think of, would help a lot.

Your Answer

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.

Browse other questions tagged or ask your own question.