full-disclosure - Re: Php gif upload thumbnail creation remote exploit

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Date: Sun, 19 Jun 2011 14:16:26 +0400
From: Владимир Воронцов
	<vladimir.vorontsov@...ec.ru>
To: "HI-TECH ." <isowarez.isowarez.isowarez@...glemail.com>
Cc: full-disclosure@...ts.grok.org.uk
Subject: Re: Php gif upload thumbnail creation remote
	exploit

http://ax330d.blogspot.com/2011/06/mosaic-of-attacks-from-image-upload.html?showComment=1308462489303#c952957474393688505

On Sun, 19 Jun 2011 02:58:16 +0200, "HI-TECH ."
<isowarez.isowarez.isowarez@...glemail.com> wrote:
> This technique describes how to exploit apps which encode pictures
during a
> Php upload. Embedding Php code inside gif files which are uploaded is a
> known technique to execute arbitrary code on a Apache Php installation.
Now
> what can one do when the code which uploads the file processes and
encodes
> the file to a thumbnail and only this thumbnail is accessible remotely
with
> the correct extension? The gif file is crunshed and the embedded Php
code
> disappears, bad situation you might think. The solution is to zero out
all
> size fields of the gif file using a hex editor. The result after the
upload
> is that the encoding routine processes the file without modifying it
> because
> of size checks. The Php code stays embedded in the file. -kc

-- 
Best regards, 
Vladimir Vorontsov
ONsec security expert

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