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I'm no security expert, so bear with me here; I just kind of tripped over something interesting that I'd like to ask about.
I was blogging about DEP based on MS' technical documentation and came up with a quick and dirty way to use a buffer overflow (we'll assume no stackguarding, or that you found a way around it i.e. using a format string bug) to kick DEP out of the way. This is pretty much based on the PaX documentation and justification for mprotect() restrictions.
In a normal shellcode attack, you have a simple process involving: - - Overwrite the return address - - Spew in some executable code - - Let RET take PC to that code and hand you control of the program
With executable protections preventing the stack from being executable, such as with DEP, a different process (hopefully) occurs: - - Overwrite the return address - - Spew in some executable code - - Segmentation fault (memory not executable) - - Program exits, attack fails
I looked at the fact that Virtual*() functions (similar to mprotect() on POSIX systems) can be used to make any area of memory executable. So, here's my way: - - Overwrite the return address - - Overwrite the stack frame pointer - - Spew in a stack frame with a return pointer to the code you injected - - Spew in some executable code - - Return to a Virtual*() function (don't know nor care which, I'm not doing the attack) - - Mark the code you injected executable - - Let RET take PC to the code you injected. You win.
Without mprotect() restrictions OR ASLR, this should be trivial to do, right?
I can't comment on SafeSEH, although I don't see screwing with exception handlers as being more interesting to a cracker than injecting your own code.
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