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Re: Firefox 0.92 DoS via TinyBMP
From: st3ng4h <st3ng4h () comcast net>
Date: Mon, 12 Jul 2004 19:22:51 -0500

On Mon, Jul 12, 2004 at 10:12:40PM +0100, Ali Campbell wrote:
I agree when you say that it's probably a flaw in the BMP lib 
implementation. But as I've pointed out once already, Windows isn't the 
only afflicted platform:

You're correct, and I'm glad you did point this out, because it may
potentially affect many such implementations.

The April bugtraq advisory that I provided URL for earlier (and
again [1]) says:

"When a BMP file loaded into the Internet Explorer (for exmaple 
'IMG' tag) the internet explorer check the BMP image size written 
in BMP file, and then allocate the necessary memory to itself for 
placing bmp image into the memory."

Also see MSDN's explanation of bitmap file structure [2] for more

AFAICT, any program/library that allocates bfSize (in 
BITMAPFILEHEADER) bytes of memory, without verifying that this 
resembles the actual size of the bitmap file, will likely suffer 
from this problem in some form or another. 

Why this was not figured out in the original advisory or this one is
beyond me; I have approximately zero experience as a bug-hunter and
am mostly ignorant to Windows internals.

What's more annoying is that the OP apparently just ripped off the
PoC from the original (incorrect) IE advisory, did not credit the
finder, and published it as a Firefox vulnerability.


[1] http://www.securityfocus.com/archive/1/360166

[2] http://msdn.microsoft.com/library/default.asp?url=/library/en-us/gdi/bitmaps_62uq.asp

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