Microsoft Security Bulletin (MS99-056)
--------------------------------------

Patch Available for "Syskey Keystream Reuse" Vulnerability
Originally Posted: December 16, 1999

Summary
=======
Microsoft has released a patch that eliminates a vulnerability in Syskey, a
utility that provides  additional protection for Microsoft(r) Windows NT(r)
password databases. The vulnerability allows  a particular cryptanalytic
attack to be effective against Syskey, significantly reducing the  strength
of the protection it offers. The patch eliminates the vulnerability and
restores strong  protection to the password database.

Frequently asked questions regarding this vulnerability can be found
at http://www.microsoft.com/security/bulletins/MS99-056faq.asp.

Issue
=====
Syskey is a utility that strongly encrypts the hashed password information
in the SAM database in  order to protect it against offline password
cracking attacks. However, Syskey reuses the  keystream used to perform some
of the encryption. This significantly reduces the strength of the
protection it provides by enabling a well-known cryptanalytic attack to be
used against it.

A patch is available that eliminates the key reuse vulnerability and again
makes it  computationally infeasible to mount a brute-force attack against
the SAM database when Syskey has  been applied.

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

Patch Availability
==================
 - x86:
   http://www.microsoft.com/Downloads/Release.asp?ReleaseID=16798
 - alpha:
   http://www.microsoft.com/Downloads/Release.asp?ReleaseID=16799

NOTE: Additional security patches are available at the Microsoft
Download Center (www.microsoft.com/downloads)

More Information
================
Please see the following references for more information related to this
issue.
 - Microsoft Security Bulletin MS99-056: Frequently Asked Questions,
   http://www.microsoft.com/security/bulletins/MS99-056faq.asp.
 - Microsoft Knowledge Base (KB) article Q248183,
   Syskey Utility Reuses Keystream,
   http://support.microsoft.com/support/kb/articles/q248/1/83.asp.
   (Note: It may take 24 hours from the original posting of this
   bulletin for this KB article to be visible.)
 - Microsoft Knowledge Base (KB) article Q143475,
   Windows NT System Key Permits Strong Encryption of the SAM,
   http://support.microsoft.com/support/kb/articles/q143/4/75.asp.
 - Microsoft Security Advisor web site,
   http://www.microsoft.com/security/default.asp.

Obtaining Support on this Issue
===============================
This is a fully supported patch. Information on contacting Microsoft
Technical Support is available at
http://support.microsoft.com/support/contact/default.asp.

Acknowledgments
===============
Microsoft acknowledges Bindview's RAZOR Security Team (www.bindview.com) for
bringing this issue  to our attention.

Revisions
=========
 - December 16, 1999: Bulletin Created.

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

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