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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