Microsoft Security Bulletin (MS99-008)

[aleph1 () UNDERGROUND ORG (aleph1 () UNDERGROUND ORG)]

The following is a Security  Bulletin from the Microsoft Product Security
Notification Service.

Please do not  reply to this message,  as it was sent  from an unattended
mailbox.
                    ********************************

Microsoft Security Bulletin (MS99-008)
--------------------------------------

Patch Available for Windows NT "Screen Saver" Vulnerability

Originally Posted: March 12, 1999

Summary
=======
Microsoft has learned of a vulnerability affecting all versions of
Microsoft(r) Windows NT(r) operating system, which could allow a user to
gain administrative privileges on a computer. In most common usage
scenarios, this vulnerability presents itself on workstations, terminal
servers, and other systems that allow non-administrative users to
interactively log on. Less-common configurations could also be affected, and
are discussed below.

A fully supported patch is available to eliminate the vulnerability, and
Microsoft recommends that affected customers download and install it, if
appropriate.

Issue
=====
Windows NT provides a screen saver feature, in which a user-selected screen
saver program is run when the machine has been idle for a specified length
of time. Windows NT initially launches a screen saver in the local system
context, then immediately changes its security context to match that of the
user. However, Windows NT does not check whether this context change was
successfully made. This is the underlying problem in this vulnerability. If
the context change can be made to fail, the screen saver will remain running
in a highly-privileged state. The risk is that a malicious user could
develop a screen saver program that, for example, uses the elevated
privileges to add the author to the Administrators group.

It is important to understand that the user must able to run exploitation
code on a machine in order to elevate their privileges. There are two types
of machines at risk:
 - Machines that allow non-administrative users to
   interactively log on. Workstation and terminal servers
   typically do allow this, but, per standard security practices,
   most other machines only allow administrators to interactively
   log on.
 - Machines that allow remote users to submit arbitrary programs
   for execution. Servers such as domain controllers, line of
   business servers, application servers, print and file servers
   and the like typically do not accept arbitrary programs for
   execution.

It also is important to note that the scope of the privilege elevation is
highly dependent on the specific machine on which the exploitation code is
run. For example, a user who exploited this vulnerability on a workstation
could join the local Administrators group, but could not directly exploit
this vulnerability to become a domain administrator. However, a user who
exploited this vulnerability on a domain controller would be able to become
a domain Administrator, because the domain SAM is shared among all domain
controllers.

While there are no reports of customers being adversely affected by this
vulnerability, Microsoft is proactively providing a patch to allow customers
to take appropriate action to protect themselves against it.

Affected Software Versions
==========================
Microsoft Windows NT Workstation 4.0
Microsoft Windows NT Server 4.0
Microsoft Windows NT Server 4.0, Enterprise Edition
Microsoft Windows NT Server 4.0, Terminal Server Edition

What Microsoft is Doing
=======================
Microsoft has released patches that fix the problem identified. The patches
are available for download from the sites listed below in What Customers
Should Do.

Microsoft also has sent this security bulletin to customers
subscribing to the Microsoft Product Security Notification Service.
See http://www.microsoft.com/security/services/bulletin.asp
for more information about this free customer service.

Microsoft has published the following Knowledge Base (KB) article on this
issue:
 - Microsoft Knowledge Base (KB) article Q221991,
   Screen Saver Vulnerability Lets User Privileges be Elevated.
   http://support.microsoft.com/support/kb/articles/q221/9/91.asp
   (Note: It might take 24 hours from the original posting of this
   bulletin for the KB article to be visible in the Web-based
   Knowledge Base.)

What Customers Should Do
========================
Microsoft recommends that customers evaluate the degree of risk that this
vulnerability poses to their systems and determine whether to download and
install the patch. The patch can be found at:
 - X86-based Windows NT Workstation and Server 4.0 (including
   Enterprise Edition):
   ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/
   usa/NT40/hotfixes-postSP4/ScrnSav-fix/Scrnsavi.exe
 - X86-based Windows NT Server 4.0, Terminal Server Edition:
   ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/
   usa/NT40TSE/hotfixes-postSP3/ScrnSav-fix/Scrnsavi.exe
 - Alpha-based Windows NT Workstation and Server 4.0 (including
   Enterprise Edition):
   ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/
   usa/NT40/hotfixes-postSP4/ScrnSav-fix/Scrnsava.exe
 - Alpha-based Windows NT Server 4.0, Terminal Server Edition:
   ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/
   usa/NT40TSE/hotfixes-postSP3/ScrnSav-fix/Scrnsava.exe

(Note: The above URLs have been wrapped for readability)

(Note: Patches for Windows NT Server 4.0, Terminal Server Edition, will not
be available immediately upon release of this bulletin, but will be released
shortly after.)

More Information
================
Please see the following references for more information related to this
issue.
 - Microsoft Security Bulletin MS99-008,
   Patch Available for Windows NT 'Screen Saver' Vulnerability
   (the Web-posted version of this bulletin),
   http://www.microsoft.com/security/bulletins/ms99-008.asp.
 - Microsoft Knowledge Base (KB) article Q221991,
   Screen Saver Vulnerability Lets User Privileges be Elevated,
   http://support.microsoft.com/support/kb/articles/q221/9/91.asp
   (Note: It might take 24 hours from the original posting of this
   bulletin for the KB article to be visible in the Web-based
   Knowledge Base.)

Obtaining Support on this Issue
===============================
If you require technical assistance with this issue, please contact
Microsoft Technical Support. For information on contacting Microsoft
Technical Support, please see
http://support.microsoft.com/support/contact/default.asp.

Revisions
=========
 - March 12, 1999: Bulletin Created


For additional security-related information about Microsoft products,
please visit http://www.microsoft.com/security


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

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS"
WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER
EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS
SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT,
INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN
IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR
LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE
FOREGOING LIMITATION MAY NOT APPLY.

(c) 1999 Microsoft Corporation. All rights reserved. Terms of Use.

   *******************************************************************
You have received  this e-mail bulletin as a result  of your registration
to  the   Microsoft  Product  Security  Notification   Service.  You  may
unsubscribe from this e-mail notification  service at any time by sending
an  e-mail  to  MICROSOFT_SECURITY-SIGNOFF-REQUEST () ANNOUNCE MICROSOFT COM
The subject line and message body are not used in processing the request,
and can be anything you like.

For  more  information on  the  Microsoft  Security Notification  Service
please    visit    http://www.microsoft.com/security/bulletin.htm.    For
security-related information  about Microsoft products, please  visit the
Microsoft Security Advisor web site at http://www.microsoft.com/security.