oss-security - Re: Offset2lib: bypassing full ASLR on 64bit Linux

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Date: Thu, 4 Dec 2014 15:47:34 -0800
From: Kees Cook <keescook@...omium.org>
To: oss-security@...ts.openwall.com
Cc: Hector Marco <hecmargi@....es>
Subject: Re: Offset2lib: bypassing full ASLR on 64bit Linux

On Thu, Dec 04, 2014 at 09:19:04PM +0100, Hector Marco wrote:
> This is a disclosure of a weakness of the ASLR Linux implementation.
> The problem appears when the executable is PIE compiled and it has an
> address leak belonging to the executable. We named this weakness:
> offset2lib.
> 
> In this scenario, an attacker is able to de-randomize all mmapped
> areas (libraries, mapped files, etc.) by knowing only an address
> belonging to the application and the offset2lib value.
> 
> We have built a PoC which bypasses on a 64 bit Linux system, the three
> most widely adopted and effective protection techniques: No-eXecutable
> bit (NX), address space layout randomization (ASLR) and stack smashing
> protector (SSP). The exploit obtains a remote shell in less than one
> second.
> 
> We have proposed the ASLRv3 which is a small Linux patch which removes
> the offset2lib weakness.
> 
> Details of the weakness, steps to exploit the offset2lib weakness, a working
> proof of concept exploit, recommendations and a demonstrative video
> has been
> publish at: http://cybersecurity.upv.es/attacks/offset2lib/offset2lib.html

Thanks for the research! Following the submission guidelines[1], please
send your ASLRv3 patch to upstream at linux-kernel@...r.kernel.org and
CC the following people:

	Andrew Morton <akpm@...ux-foundation.org>
	Thomas Gleixner <tglx@...utronix.de>
	Ingo Molnar <mingo@...hat.com>
	"H. Peter Anvin" <hpa@...or.com>
	Russell King <linux@....linux.org.uk>
	Catalin Marinas <catalin.marinas@....com>
	Will Deacon <will.deacon@....com>
	Oleg Nesterov <oleg@...hat.com>
	Andy Lutomirski <luto@...capital.net>
	Kees Cook <keescook@...omium.org>

I noticed in testing that this hugely reduces the available mmap space
available to 32-bit processes. I suspect this is what this wasn't done
before.

Thanks!

-Kees

[1] https://www.kernel.org/doc/Documentation/SubmittingPatches

-- 
Kees Cook
Chrome OS Security

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