REVISED: Microsoft Security Bulletin MS02-050: Certificate Validation Flaw Could Enable Identity Spoofing (329115)

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Title:      Certificate Validation Flaw Could Enable Identity
            Spoofing (329115)
Date:       September 4,2002 (Revised November 11, 2003)
Software:   Microsoft Windows 98 
            Microsoft Windows 98 Second Edition 
            Microsoft Windows Me 
            Microsoft Windows NT(r) 4.0 
            Microsoft Windows NT 4.0, Terminal Server Edition 
            Microsoft Windows 2000 
            Microsoft Windows XP 
            Microsoft Office for Mac 
            Microsoft Internet Explorer for Mac 
            Microsoft Outlook Express for Mac 

Impact:     Identity spoofing and, in some cases, ability to gain 
            control over a user's system.
Max Risk:   Important   
Bulletin:   MS02-050

Microsoft encourages customers to review the Security Bulletin at:
     http://www.microsoft.com/technet/security/bulletin/MS02-050.asp 
  
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Reason for Revision:
====================
Microsoft re-issued this security bulletin on November 11, 2003 to 
advise on the availability of an updated Microsoft Windows 2000
Service Pack 4 (SP4) security patch. This revised security patch 
corrects a regression that may occur during the installation of 
Microsoft Internet Explorer 6.0 Service Pack 1 on Windows 2000 SP4. 
This regression removes the update that is discussed in this bulletin
and that is provided as part of Windows 2000 SP4. Customers who are 
using Windows 2000 SP4 and then installed Internet Explorer 6.0 
Service Pack 1 should apply the updated Windows 2000 SP4 security 
patch to help protect from this vulnerability.

Issue:
======
The vulnerability identified in the original version of the bulletin 
could enable an attacker who had a valid end-entity certificate to 
issue a subordinate certificate that, although bogus, would 
nevertheless pass validation. Because CryptoAPI is used by a wide 
range of applications, this could enable a variety of identity 
spoofing attacks. 

Mitigating Factors:
====================
*   The user could always manually check a certificate chain, and 
might notice in the case of a spoofed chain that there was an 
unfamiliar intermediate CA. 
*   Unless the attacker's digital certificates were issued by a CA 
in the user's trust list, the certificate would generate a 
warning when validated. 
*   The attacker could only spoof certificates of the same type as 
the one he or she possessed. In the case where the attacker 
attempted an attack using a high-value certificate such as 
Authenticode certificates, this would necessitate obtaining a 
legitimate certificate of the same type - which could require 
the attacker to prove his or her identity or entitlement to the 
issuing CA. 

Risk Rating:
============
 - Important

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read the 
   Security Bulletin at
     http://www.microsoft.com/technet/security/bulletin/MS02-050.asp 
   for information on obtaining this patch.

Acknowledgment:
===============
 - UK National Infrastructure Security Co-ordination Centre (NISCC)
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