Microsoft Security Bulletin MS03-023: Buffer Overrun In HTML Converter Could Allow Code Execution (Q823559)

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Title:      Buffer Overrun In HTML Converter Could Allow Code 
            Execution (823559)
Date:       09 July 2003
Software:   Microsoft(r) Windows (r) 98
            Microsoft Windows 98 Second Edition 
            Microsoft Windows Me 
            Microsoft Windows NT 4.0 
            Microsoft Windows NT 4.0 Terminal Services Edition 
            Microsoft Windows 2000 
            Microsoft Windows XP 
            Microsoft Windows Server 2003  
Impact:     Allow an attacker to execute code of their choice
Max Risk:   Critical
Bulletin:   MS03-023

Microsoft encourages customers to review the Security Bulletins 
at: 
http://www.microsoft.com/technet/security/bulletin/MS03-023.asp
http://www.microsoft.com/security/security_bulletins/ms03-023.asp
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Issue:
======

All versions of Microsoft Windows contain support for file 
conversion within the operating system. This functionality allows 
users of Microsoft Windows to convert file formats from one to 
another. In particular, Microsoft Windows contains support for 
HTML conversion within the operating system. This functionality 
allows users to view, import, or save files as HTML. 

There is a flaw in the way the HTML converter for Microsoft 
Windows handles a conversion request during a cut-and-paste 
operation. This flaw causes a security vulnerability to exist. A 
specially crafted request to the HTML converter could cause the 
converter to fail in such a way that it could execute code in the 
context of the currently logged-in user. Because this 
functionality is used by Internet Explorer, an attacker could 
craft a specially formed Web page or HTML e-mail that would cause 
the HTML converter to run arbitrary code on a user's system. A 
user visiting an attacker's Web site could allow the attacker to 
exploit the vulnerability without any other user action. 

To exploit this vulnerability, the attacker would have to create 
a specially-formed HTML e-mail and send it to the user. 
Alternatively, an attacker would have to host a malicious Web 
site that contains a Web page designed to exploit this 
vulnerability. The attacker would then have to persuade a user to 
visit that site. 


Mitigating factors: 
====================

 - By default, Internet Explorer on Windows Server 2003 runs in 
Enhanced Security Configuration. This default configuration of 
Internet Explorer blocks automatic exploitation of this attack. 
If Internet Explorer Enhanced Security Configuration has been 
disabled, the protections put in place that prevent this 
vulnerability from being automatically exploited would be 
removed. 

 - In the Web-based attack scenario, the attacker would have to 
host a Web site that contained a Web page used to exploit this 
vulnerability. An attacker would have no way to force users to 
visit a malicious Web site outside the HTML e-mail vector. 
Instead, the attacker would need to lure them there, typically by 
getting them to click a link that would take them to the 
attacker's site. 

 - Exploiting the vulnerability would allow the attacker only the 
same privileges as the user. Users whose accounts are configured 
to have few privileges on the system would be at less risk than 
ones who operate with administrative privileges. 

Risk Rating:
============
Critical

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read 
the  Security Bulletins at
   
http://www.microsoft.com/technet/security/bulletin/ms03-023.asp
http://www.microsoft.com/security/security_bulletins/ms03-023.asp
   
   for information on obtaining this patch.


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