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Date: Thu, 14 Jul 2011 07:02:48 -0400
From: Dan Rosenberg <dan.j.rosenberg@...il.com>
To: oss-security@...ts.openwall.com
Cc: Jan Lieskovsky <jlieskov@...hat.com>, "Steven M. Christey" <coley@...us.mitre.org>, 
	Secunia Research <vuln@...unia.com>
Subject: Re: Re: CVE Request -- libsndfile -- Integer overflow
 by processing certain PAF files

On Thu, Jul 14, 2011 at 2:49 AM, Erik de Castro Lopo
<erikd@...a-nerd.com> wrote:
> Jan Lieskovsky wrote:
>
>>    an integer overflow, leading to heap-based buffer overflow flaw was
>> found in the way libsndfile, library for reading and writing of sound
>> files, processed certain PARIS Audio Format (PAF) audio files with
>> crafted count of channels in the PAF file header. A remote attacker
>> could provided a specially-crafted PAF audio file, which once opened by
>> a local, unsuspecting user in an application, linked against libsndfile,
>> could lead to that particular application crash (denial of service),
>
> I agree with everything up to here.
>
>> or, potentially arbitrary code execution with the privileges of the
>> user running the application.
>
> but this is rubbish. The heap gets overwritten with zeros which would
> certainly lead to the application segfaulting. However, there is
> no way for arbitrary code to be executed on amy sane OS with proper
> memory protection.

This is not a sound assumption.  Any sort of partially controlled heap
corruption, even if the data that's being written isn't controllable
by an attacker, should be considered potentially exploitable.  Modern
heap exploitation is alive and well - it's worth pointing out that a
recent remote vulnerability in Microsoft IIS FTPD that allowed for a
heap overflow of strictly 0xff bytes was shown to be exploitable,
contradicting Microsoft's claims that it could only cause denial of
service.  Think about partially overwriting certain elements of heap
metadata, or even heap data, with zeroes.  Suppose an application with
heavy function pointer usage was linked against libsndfile, and this
overflow allowed overwriting the least significant bytes of a function
pointer with zeroes and ultimately allowed for controlling execution
flow.

It's better to be safe than sorry.

Regards,
Dan

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