-----Original Message-----
From: Microsoft
[mailto:[EMAIL PROTECTED]
osoft.com] 
Sent: Wednesday, January 30, 2002 20:57
To: 
Subject: Microsoft Security Bulletin MS02-001


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Title:      Trusting Domains Do Not Verify Domain Membership of 
            SIDs in Authorization Data
Date:       30 January 2002 
Software:   Windows NT 4.0, Windows 2000
Impact:     Privilege Elevation
Max Risk:   Moderate 
Bulletin:   MS02-001

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS02-001.asp.
- ----------------------------------------------------------------------

Issue:
======
Trust relationships are created between Windows NT or Windows 2000
domains to allow users in one domain to access resources in other
domains without requiring them to authenticate separately to each
domain. When a user in a trusted domain requests access to a resource in
a trusting domain, the trusted domain supplies authorization data in the
form of a list of Security Identifiers (SIDs) that indicate the user's
identity and group memberships. The trusting domain uses this data to
determine whether to grant the user's request. 

A vulnerability exists because the trusting domain does not verify that
the trusted domain is actually authoritative for all the SIDs in the
authorization data. If one of the SIDs in the list identified a user or
security group that is not in the trusted domain, the trusting domain
would accept the information and use it for subsequent access control
decisions. If an attacker inserted SIDs of his choice into the
authorization data at the trusted domain, he could elevate his
privileges to those associated with any desired user or group, including
the Domain Administrators group for the trusting domain. This would
enable the attacker to gain full Domain Administrator access on
computers in the trusting domain. 

Exploiting this vulnerability would be difficult, and require
administrative privileges on the trusted domain, as well as the
technical wherewithal to modify low-level operating system functions and
data structures. 
 - Windows NT 4.0 provides no mechanism by which additional 
   SIDs could be added to authorization data. To exploit the
   vulnerability, an attacker would need to develop and 
   install custom operating system components to add the
   SIDs. 
 - Windows 2000 does provide a mechanism for introducing 
   additional SIDs into authorization data, known as 
   SIDHistory. However, there is no programming interface that
   would allow an attacker - even with administrative rights - 
   to introduce a desired SID into the SIDHistory information; 
   instead, an attacker would need to perform a binary edit of
   the data structures that hold the SIDHistory information. 

Microsoft has developed a mechanism called SID Filtering that eliminates
the vulnerability and adds further protection between trusting domains.
When installed and enabled on the domain controllers of a trusting
domain, SID Filtering causes the system to inspect all incoming
authorization data and remove any SIDs that do not identify a user or
security group that is defined in the trusted domain. 

There are, however, tradeoffs associated with using the SID Filtering
mechanism. These are summarized in the FAQ and Caveats sections below,
and are discussed in detail in Microsoft Knowledge Base article Q289243
and in a technical white paper
(http://www.microsoft.com/windows2000/techinfo/administration/security
/sidfilter.asp) that Microsoft strongly urges administrators to read
before using SID Filtering. This is especially important in the case of
administrators who are in the midst of migrating their networks from
Windows NT 4.0 to Windows 2000.

Mitigating Factors:
====================
 - The attacker would need to have domain administrator privileges
   in the trusted domain in order to exploit the vulnerability. 
 - The attacker's domain would need to already be trusted by 
   the target domain, or the target domain's administrator would
   need to approve the establishment of a new trust relationship.
 - There is no capability for the attacker to unilaterally 
   initiate a trust relationship with another domain or cause it
   to trust the attacker's domain. 
 - The attacker would need to modify operating system components 
   and data.

Risk Rating:
============
 - Internet systems: Low
 - Intranet systems: Moderate
 - Client systems: None

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read the 
   Security Bulletin at
   http://www.microsoft.com/technet/security/bulletin/ms02-001.asp
   for information on obtaining this patch.

Acknowledgment:
===============
 - Aelita Software (http://www.aelita.com) 
 - Michel Trepanier of CMT Inc. and Loto-Quebec.

- ---------------------------------------------------------------------

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WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN
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DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
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