full-disclosure - Re: memory required for a PNG file

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Message-ID: <20090724054719.GA21846@lboro.ac.uk>
Date: Fri, 24 Jul 2009 06:47:19 +0100
From: A.L.M.Buxey@...ro.ac.uk
To: Murthy N Srinivas-B22237 <ssmurthy.nittala@...escale.com>
Cc: full-disclosure@...ts.grok.org.uk
Subject: Re: memory required for a PNG file

Hi,
> Hi
> How do we calculate memory required for a PNG file from the dimensions
> of width and height contained in the file?
> It seems that attackers make use width and height to take control of
> clients.

just from H+W? you cant - you'd have to know oher things such as
depth, alpha layer presence, ancillary data container, gamma info.
given that most attacks using images are using some buffer overflow
in the parser you *might* be able to write your own 'PNG viewer'
that would check the the image is sane and hope you hadnt
coded any mistakes too... ;-)

alan

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