Re: Is DEP easily evadable?

[John Richard Moser <nigelenki () comcast net>]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1



Florian Weimer wrote:
> * John Richard Moser:
>
>
> > 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.
>
>
> Look for return-into-libc exploits.  There are quite a few.
>
> Even with non-executable stack and heap, no one guarantees that buffer
> overflows aren't exploitable.  Randomization of load addresses is
> intended to provide additional protection, but the number of available
> bits is fairly low on 32 bit machines (problably less than 16).  I
> don't know if Windows is doing it.

I don't see anything in the docs about it, but I don't have XP (I think
I have an XP license. . . yeah here it is, taped to the bottom of my
laptop; but I don't have a CD, and don't feel like finding . . what are
those things. . . a torrent of it)

PaX does pretty nice randomization.  I think 15/16 for heap and stack
and 24 for mmap(), though I could be overshooting the 24.  I'm on amd64
so I can't just run paxtest and see; though I could read the source code.

Also, there appears to be a UUDecode() function available! :)  Looks
like you might be able to do attacks with NULLs in the shellcode and such?

Oh well, I guess this is just redundant white noise then; I was just
struck dumb a bit when it appeared that HW-DEP provided nothing in the
way of real protection; I'm too used to security enhancements being real.


- --
All content of all messages exchanged herein are left in the
Public Domain, unless otherwise explicitly stated.

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.0 (GNU/Linux)
Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org

iD8DBQFB5sCYhDd4aOud5P8RAn+VAKCKTEfka1sMzEdL9xliKEDJDsGxEgCgkFI4
ph+fJOcB0ELonMpX/Px2RxY=
=Mctm
-----END PGP SIGNATURE-----