bugtraq - Re: Crash IE with 11 bytes ;)

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Date: Wed, 28 Jul 2004 17:02:17 +0200
From: "Berend-Jan Wever" <skylined@...p.tudelft.nl>
To: <full-disclosure@...ts.netsys.com>, <bugtraq@...urityfocus.com>
Subject: Re: Crash IE with 11 bytes ;)

Here's a detailed description of what's going wrong with [STYLE]@;/*

The problem is the unterminated comment "/*"; IE computes the length of the comment for a memcpy opperation by substracting the end pointer form the start pointer. The comment starts behind "/*" and should end at "*/", but since there is no terminator, the start of the string is used. IE there for calculates the string to be -2 unicode characters long. The subsequent memcpy will try to copy 0xFFFFFFFE bytes untill it gets a read or write exception. (You will see the offending instruction is a REP MOVSD)

Unfortunately for us hackers, I believe you cannot control the length value for the memcpy other then setting it to -2. So you will always cause a read or write exception. You will only overwrite a small part of the heap before the exception is caused so overwriting the SEH to controlling execution is also ruled out.

Conclusion: lame DoS

I did find another way to use this to cause an exception at a different location:
[SCRIPT]
  d = window.open().document;
  d.write("x");
  d.body.innerHTML = "<STYLE>@;/*";
[/SCRIPT]
This will crash because of a null pointer in a CMP [ESI], 0.
It didn't look interesting to me, so no detailed investigation.

Cheers,
SkyLined

----- Original Message ----- 
From: "Phuong Nguyen" <phuong@...urity.com>
To: <full-disclosure@...ts.netsys.com>
Sent: Friday, July 23, 2004 19:17
Subject: [Full-Disclosure] Crash IE with 11 bytes ;)

> Hey,
> 
> I thought you guys might want to know that it only takes 11 bytes to crash 
> IE 5.x , 6.x SP1. CSS memory corruption vulnerability. All you need to do 
> is <style>;@/* ;) simple as that. More details@ 
> http://www.ecqurity.com/adv/IEstyle.html
> 
> Phuong
> 
> 
> _______________________________________________
> Full-Disclosure - We believe in it.
> Charter: http://lists.netsys.com/full-disclosure-charter.html

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Full-Disclosure - We believe in it.
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