Microsoft Internet Explorer (mshtml.dll) - Remote Code Execution

[advisories () computerterrorism com]

Computer Terrorism  (UK) :: Incident Response Centre
======================================


Security Advisory :: CT22-03-2006
-------------------------------------------


Title:                  Microsoft Internet Explorer (mshtml.dll) - Remote Code Execution

Organisation:           Computer Terrorism (UK)
Web:                    www.computerterrorism.com
Advisory Date:          22nd March, 2006


Affected Software:              Microsoft Internet Explorer 6.x, IE7 Beta 2
Severity:                       Critical
Impact:                 Remote System Access
Solution Status:                ** UNPATCHED **


Overview:
-------------
 
Pursuant to the publication of the aforementioned bug/vulnerability, this document serves as a preliminary Security 
Advisory for users of Microsoft Internet Explorer version 6 and 7 Beta 2.

Successful exploitation will allow a remote attacker to execute arbitrary code against a fully patched Windows XP 
system, yielding system access with privileges of the underlying user.

 

Technical Narrative:
-------------------------
 
As per the publication, the bug originates from the use of a createTextRange() method, which, under certain 
circumstances, can lead to an invalid/corrupt table pointer dereference. 
 
As a result, IE encounters an exception when trying to call a deferenced 32bit address, as highlighted by the following 
sniplet of code.
 
0x7D53C15D MOV ECX, DWORD PTR DS:[EDI]
..
0x7D53C166 CALL DWORD PTR [ECX]
 
Due to the incorrect reference, ECX points to a very remote, non-existent memory location, causing IE to crash (DoS). 
However, although the location is some what distant, history dictates that a condition of this nature is conducive 
towards reliable exploitation.
 
 
Proof of Concept:
-----------------------
 
Computer Terrorism (UK) can confirm the production of reliable proof of concept (PoC) for this vulnerability (tested on 
Windows XP SP2). However, until a patch is developed, we will NOT be publicly disclosing our research.



Temporary Solution:
-------------------------
 
Users are advised to disable active scripting for non-trusted sites until a patch is released.
 

Vendor Status:
--------------------
 
The Vendor has been informed of all aspects of this new vulnerability (including PoC), but as of the date of the 
document, this vulnerability is UNPATCHED.