Re: Exploit writing when EIP is not corrupted but EDX, EBP register are having user supplied data

[Michal Zalewski <lcamtuf () coredump cx>]

> I had a condition where "EDX and EBP registers are filled with user supplied data but EIP is not getting corrupted".
> How can I write a working exploit to this?

There is no simple answer - it depends on what is being done with
these registers at the time of the crash (if anything at all - inspect
what's under eip), and what else happened or could have happened in
the code between the original coding error and the crash location.

In many cases, seeing attacker-controlled content in general-purpose
registers is just a red herring: this data may be left over from any
earlier operations that processed said data, and the crash itself may
be a simple NULL pointer dereference or somesuch. Consequently, the
absence of "AAAA" in any register does not mean that the condition
that got you to this crash did not involve overwriting something
important in an attacker-controlled manner (particularly common with
race conditions and memory corruption).

/mz

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