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Date: Fri, 15 Jul 2011 10:25:16 +0200
From: Jan Lieskovsky <>
To: Erik de Castro Lopo <>
        "Steven M. Christey" <>,
        Secunia Research <>
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:

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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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