REVISED: Microsoft Security Bulletin MS03-007: Unchecked Buffer In Windows Component Could Cause Server Compromise (815021)

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Title:      Unchecked Buffer In Windows Component Could Cause 
            Server Compromise (815021)
Released:   17 Mar 2003
Revised:    28 May 2003 (version 3.0)
Software:   Microsoft (r) Windows (r) NT 4.0, Windows 2000 and    
            Windows XP
Impact:     Run code of attacker's choice
Max Risk:   Critical
Bulletin:   MS03-007

Microsoft encourages customers to review the Security Bulletin 
at: 
http://www.microsoft.com/technet/security/bulletin/MS03-007.asp
http://www.microsoft.com/security/security_bulletins/ms03-007.asp
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Reason for Revision:
====================
Microsoft originally released this security bulletin on March 17, 
2003. At that time, Microsoft was aware of a publicly available 
exploit that was being used to attack Windows 2000 Servers running 
IIS 5.0. The attack vector in this case was WebDAV although the 
underlying vulnerability was in a core operating system component, 
ntdll.dll. Microsoft issued a patch to protect Windows 2000 
customers shortly afterwards, but also continued to investigate the 
underlying vulnerability. During the course of that investigation, 
Microsoft found that Windows NT 4.0 also contains the underlying 
vulnerability in ntdll.dll, however it does not support WebDAV and 
therefore the known exploit was not effective against Windows NT 
4.0. In addition, Microsoft has recently been made aware of this 
vulnerability as well in Windows XP. However, like Windows NT 4.0, 
Windows XP does not install Internet Information Services (IIS) by 
default. Microsoft has now released patches for Windows NT 4.0 and 
Windows XP.

Issue:
======
Microsoft Windows 2000 supports the World Wide Web Distributed 
Authoring and Versioning (WebDAV) protocol. WebDAV, defined in 
RFC 2518, is a set of extensions to the Hyper Text Transfer 
Protocol (HTTP) that provide a standard for editing and file 
management between computers on the Internet. A security 
vulnerability is present in a Windows component used by WebDAV 
and results because a core operating system component, ntdll.dll, 
contains an unchecked buffer. 

An attacker could exploit the vulnerability by sending a 
specially formed HTTP request to a machine running Internet 
Information Server (IIS). The request could cause the server to 
fail or to execute code of the attacker's choice. The code would 
run in the security context of the IIS service (which, by 
default, runs in the LocalSystem context). 

Although Microsoft has supplied a patch for this vulnerability 
and recommends all affected customers install the patch 
immediately, additional tools and preventive measures have been 
provided that customers can use to block the exploitation of 
this vulnerability while they are assessing the impact and 
compatibility of the patch. These temporary workarounds and 
tools are discussed in the "Workarounds" section in the FAQ 
below.

Mitigating Factors:
====================
 - URLScan, which is a part of the IIS Lockdown Tool will block 
this attack in its default configuration 
 - The vulnerability can only be exploited remotely if an attacker 
can establish a web session with an affected server 
 - Windows NT 4.0 and Windows XP do not install Internet 
Information Services by default. 
 - Windows NT 4.0 does not support WebDAV 


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/ms03-007.asp
http://www.microsoft.com/security/security_bulletins/ms03-007.asp
   
   for information on obtaining this patch.


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