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Date: Fri, 15 Jul 2011 10:25:16 +0200
From: Jan Lieskovsky <jlieskov@...hat.com>
To: Erik de Castro Lopo <erikd@...a-nerd.com>
CC: oss-security@...ts.openwall.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
Hello Erik,
On 07/15/2011 02:47 AM, Erik de Castro Lopo wrote:
>
> Please CC me on all mails regarding this bug. I am not on the list
> where Dan Rosenberg wrote:
There was only one reaction from Dan so far:
[1] http://comments.gmane.org/gmane.comp.security.oss.general/5476
The oss-security list and it's content / archive are publicly accessible:
[2] http://oss-security.openwall.org/wiki/mailing-lists/oss-security
You can subscribe there and / or use one of the ways to access the archive:
[3] http://www.openwall.com/lists/oss-security/
[4] http://news.gmane.org/gmane.comp.security.oss.general
(plus others)
No need to be Cc-ed on each particular message, just use the thread view
[4], and react to message, where necessary / appropriate.
Thank you && Regards, Jan.
--
Jan iankko Lieskovsky / Red Hat Security Response Team
>
>> On Thu, Jul 14, 2011 at 2:49 AM, Erik de Castro Lopo
>> <erikd (AT) mega-nerd (DOT) 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.
>
> The code which caused the heap overflow was this:
>
> memset (ppaf24->samples, 0, ppaf24->samplesperblock * ppaf24->channels) ;
>
> where it was the ppaf24->channels value that was not validated (and
> ppaf24->samplesperblock is always 10). In future versions of libsndfile
> ppaf24->samplesperblock will be replaced by a compile time constant
> value.
>
> That means that the heap is overwritten in blocks that are a multiple
> of 10 bytes which makes it significatly more difficult to exploit.
>
>> 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.
>
> For this instance of heap overflow (overwritten in multiples of 10 bytes
> with the base being 4 byte aligned), its only possible to zero the lowest
> 2 bytes of a function pointer (assuming a little endian machine) if it
> happens to lie in exactly the right place.
>
> In terms of ease of exploitation, this one has to be in the very difficult
> basket.
>
>> It's better to be safe than sorry.
>
> That's why I rushed out a new release. I do take this seriously, but
> I do not like to see the threat exaggerated beyond reason.
>
> Erik
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