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Date: Tue, 19 May 2015 16:20:15 +0200
From: Andrea Palazzo <>
To: Stanislav Malyshev <>
Subject: Re: CVE Request + Advisory: PHP str_repeat() sign mismatch based
 memory corruption

Hi again!

My point is: once you get to have a corrupted zval, there are tons of 
functions that would result in memory errors if working on it.
A str_repeat() with user-supplied arguments is not so common at all, but 
let's say you have it (e.g.,, it is really likely 
that it would end up processed by one of these functions (string 
concatenation, for example).

$makernote  <>  .=str_repeat  <>("\x00",($tiff_data  <>[ 'Makernote_Tag' ][ 'Offset' ] - 8 ) );

On 19/05/2015 00:43, Stanislav Malyshev wrote:
> Hi!
>> About code execution, I haven't had the chance to focus on actual
>> exploitation yet (I surely will in the near future), but as you can see
>> from the original report (, I
>> pointed out several cases in which working on a so-crafted zval would
>> lead to invalid memory access (with user controlled values as well), so
>> I am pretty confident it is achievable.
> These examples all seem to require specific code (like
> 'md5(str_repeat("a", 4294967294-1));') to be run. The probability that
> applications would contain this specific code with str_repeat argument
> controlled by remote user seems to be pretty low. However, if you can
> show exploiting this on a code of an application that is not specially
> crafted to demonstrate this issue, or at least resembles code that is
> likely to be deployed in a real application, I will gladly change my
> opinion.

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