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Re: Exploiting buffer overflows via protected GCC
From: ArcSighter Elite <arcsighter () gmail com>
Date: Mon, 16 Feb 2009 09:00:33 -0500

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James Matthews wrote:
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 () suse 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 () uboo:~$ cat bof.c
#include <stdio.h>
#include <string.h>

int main()
{

char buf[512];

memset(buf, 'A', 528);

return 0;

}
jason () uboo:~$

jason () uboo:~$ ./bof
*** stack smashing detected ***: ./bof terminated
======= Backtrace: =========
/lib/tls/i686/cmov/libc.so.6(__fortify_fail+0x48)[0xb7f08548]
jason () uboo:~$

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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------------------------------------------------------------------------

_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/

Ubuntu and recent kernels also implement ASLR. So, that may be the
issue, besides StackGuard.

Sincerely.
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_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/


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