full-disclosure - Re: Exploiting buffer overflows via protected GCC

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Message-ID: <8a6b8e350902141347g45591bdbr6f1828f8b305410c@mail.gmail.com>
Date: Sat, 14 Feb 2009 23:47:35 +0200
From: James Matthews <nytrokiss@...il.com>
To: Marcus Meissner <meissner@...e.de>
Cc: full-disclosure@...ts.grok.org.uk
Subject: Re: Exploiting buffer overflows via protected GCC

I would recommend doing the following things.

1. Ask on the Ubuntu GCC list what protection is implemented. (Or just look
at the source)
2. Use GCC to see where the execution is being redirected and so you can
have a better visual of whats going on.
3. Are you sure the stack is executable?



On Sat, Feb 14, 2009 at 12:30 AM, Marcus Meissner <meissner@...e.de> wrote:

> On Fri, Feb 13, 2009 at 11:50:11AM -0500, Jason Starks wrote:
> > I came across a problem that I am sure many security researchers have
> seen
> > before:
> >
> > jason@...o:~$ cat bof.c
> > #include <stdio.h>
> > #include <string.h>
> >
> > int main()
> > {
> >
> > char buf[512];
> >
> > memset(buf, 'A', 528);
> >
> > return 0;
> >
> > }
> > jason@...o:~$
> >
> > jason@...o:~$ ./bof
> > *** stack smashing detected ***: ./bof terminated
> > ======= Backtrace: =========
> > /lib/tls/i686/cmov/libc.so.6(__fortify_fail+0x48)[0xb7f08548]
> > jason@...o:~$
> >
> > I have googled my brains out for a solution, but all I have gathered is
> that
> > my Ubuntu's gcc is compiled with SSP and everytime I try to overwrite the
> > return address it also overwrites the canary's value, and triggers a stop
> in
> > the program. I've disassembled it and anybody who can help me probably
> > doesn't need me to explain much more, but I would like to know a way to
> get
> > this. There seems to be some people on this list who may know something
> on
> > how to exploit on *nix systems with this protection enabled.
> >
> > I do not want to just disable the protection and exploit it normally, I
> want
>
> Perhaps you should learn first exactly _what_ caught your buffer overflow.
>
> Hint: It was not SSP aka -fstack-protector.
>
> Ciao, Marcus
>
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