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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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