Re: Symlink vulnerabilities

[xD 0x41 <secn3t () gmail com>]

ln actually succeeds, but created /tmp/foo/foo instead. The attacker still
owns /tmp/foo, so he quickly rename()s it and replaces /tmp/foo with his
exploit.

You can make it bypass Aslr ?
This is what im talking about tavis, not the well known ln and other bugs
you have pleasured us all with :)
THIS one, cannot be won.
proove it, it is a shitty poc, i cannot get passed the break when it
symlinks across using ln, it triggers something, and shuts whatever down..
Your audit and kcopes audit bugs, work alittle differently..
This PoC is a *fail* Tavis, you would otherwise have made it into a real poc
that actually spawns root , yes even in cron if what your saying is right ,
no?
Im saying, Kernel will shut your PoC down, your saying it wont.
Proove me wrong , coz sofar, many have tried and many have failed.
it does not even need be disclosed, i dont mind.
i would be happy thelp fix a bug within the kernel but, we both know this is
not within kernel land,it is a bug in another area,
It still must bypass atleast ASLR on vanilla to be called a real poc,and be
treated as such by the secteam of Ubuntu and debian, of wich, they dont seem
to be in any hurry atall about this one, where, your ones, and kcopes, they
were VERY prompt to jump on.
i believe many have recreated it, but simply cannnot get it to spawn a
stable enough root shell.
Your the brains in bash, i wont deny you this, but i do not se this one
working Tavis :s
Please, by all means, proove it and Vladz name is clear. Otherwise to me is
just another exposed failed poc wich is screaming for ubuntu devteam to give
a crap :s.
My outlook is bleak, yes, but i was part of one of such teams years ago,
altho, i wont go into that now, it is not even part of this OS, so, I do
know how secteams somewhat work, they prioritise things.
if a bug is being used like crazy to exploit, they will simply implant some
new binarys, along with theyre kernel..and possibly update bzexe and bunzip
etc, all of wich have had many flaws, i just dont think a race condition can
be won in this case.
Thats from actual hard code exploits not running because of aslr, on the
simplest of setups even.
Its already out, this infos, so, if you think it also leads to root, then i
would expect YOU of all people to be alot more proactive about it.
Your not though.
I appreciate the time you have taken but, i believe you wont win this race
:).
Have a nice day.
xd


On 25 October 2011 21:06, Tavis Ormandy <taviso () cmpxchg8b com> wrote:

> xD 0x41 <secn3t () gmail com> wrote:
>
> > Hello,
> >     Your 'race condition possibly leading to root'is a myth...
> > Yes thats maybe because race condition or not, it is ASLR wich will
> > prevent from ANY rootshell,and Yes, it has bveen tried... You can do
> > better, go right ahed ;-) I am betting you thats why it aint being
> ptached
> > in any hurry, because obv if you read some notes about it in the
> committs,
> > you will see they must have reproduced the said bugs, in and with, more
> > than JUST bzexe even... but anyhow, your PoC is bs.
>
> I think you misunderstood, he's not talking about memory corruption, his
> attack sounds like a legitimate filesystem race. I'll try to explain, the
> bzexe utility compresses executables and then decompresses them at runtime
> by prepending a decompression stub.
>
> His attack is against the stub, which is a bourne shell script. It
> basically
> does this:
>
>    1. Safely decompress the original executable inside /tmp using tempfile.
>    2. Create a hardlink to the decompressed executable with the same name
> of the original input (this is a trick to maintain argv[0], which is not as
> easy in bourne as it is in modern shells).
>    3. Execute the hardlink with the requested parameters.
>
> His attack is against stage 2, he points out that although it is safe to
> use
> the link() system call in /tmp, the ln(1) utility does some convenience
> processing if you pass it a directory name.
>
> So, the attack scenario would be that root executed a bzexe compressed
> executable called foo, and then he creates the directory /tmp/foo, and
> makes
> it 777.
>
> ln actually succeeds, but created /tmp/foo/foo instead. The attacker still
> owns /tmp/foo, so he quickly rename()s it and replaces /tmp/foo with his
> exploit.
>
> Now root executes it, and gives him a root shell.
>
> Vladz suggests using -F, which will solve this problem by telling ln to use
> the directory name instead. This will work nicely.
>
> > Make it then ill
> > believe it, ask others, you wont beat aslr on even vanilla,. So, stop
> > complaining you did not get into patch- halll of flame.. it was not
> really
> > going to be ever exploited, or you would surely not be the one posting
> > this ;) Anyhow, nice try but no banana. xd
>
> I think it's quite a nice example, and a nice simple solution. Imagine a
> system where crond executes a bzexe utility at regular intervals, Vladz'
> attack will eventually succeed.
>
> Tavis.
>
> > On 24 October 2011 05:55, vladz <vladz () devzero fr> wrote:
> >
> > > On Fri, Oct 21, 2011 at 07:59:59PM -0400, bugs () fbi dhs org wrote:
> > > > bzexe utility:
> > > >
> > > > /bin/bzexe:tmp=gz$$ /bin/bzexe:rm -f zfoo[12]$$
> > >
> > > I reported this one several months ago (in some conditions it could
> lead
> > > to a root exploit) and provided an easy solution, but no updates:
> > >
> > >  http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=632862
> > >
> > > -- http://vladz.devzero.fr PGP key 8F7E2D3C from pgp.mit.edu
> > >
> > > _______________________________________________ Full-Disclosure - We
> > > believe in it. Charter:
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>
>
> --
> -------------------------------------
> taviso () cmpxchg8b com | pgp encrypted mail preferred
> -------------------------------------------------------
>
> _______________________________________________
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