Microsoft Security Bulletin MS99-056 - Critical
Patch Available for "Syskey Keystream Reuse" Vulnerability
Published: December 16, 1999
Originally Posted: December 16, 1999
Microsoft has released a patch that eliminates a vulnerability in Syskey, a utility that provides additional protection for Microsoft® Windows NT® 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/technet/security/bulletin/fq99-056.mspx.
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
Vulnerability Identifier: CVE-1999-0994
Windows NT Workstation 4.0, Server 4.0, and Server 4.0, Enterprise Edition:
Window NT Server 4.0, Terminal Server Edition:
This vulnerability is eliminated in Service Pack 6 for Windows NT 4.0 Server, Terminal Server Edition.
NOTE: This patch also eliminates the "Malformed Security Identifier Request" vulnerability.
NOTE: Additional security patches are available at the Microsoft Download Center
Please see the following references for more information related to this issue.
Microsoft Security Bulletin MS99-056: Frequently Asked Questions, http://www.microsoft.com/technet/security/bulletin/fq99-056.mspx.
Microsoft Knowledge Base (KB) article 248183, Syskey Utility Reuses Keystream, http://support.microsoft.com/default.aspx?scid=kb;en-us;248183&sd=tech.
(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 143475, Windows NT System Key Permits Strong Encryption of the SAM, http://support.microsoft.com/default.aspx?scid=kb;en-us;143475&sd=tech.
Microsoft Security Advisor web site, http://www.microsoft.com/security/default.mspx.
Obtaining Support on this Issue
This is a fully supported patch. Information on contacting Microsoft Technical Support is available at http://support.microsoft.com/contactussupport/?ws=support.
Microsoft acknowledges Bindview's RAZOR Security Team (www.bindview.com) for bringing this issue to our attention.
- December 16, 1999: Bulletin Created.
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