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Microsoft Security Bulletin (MS00-024)

Tool Available for "OffloadModExpo Registry Permissions" Vulnerability

Originally Posted: April 12, 2000

Summary

Microsoft has released a tool that installs tighter permissions on a Windows NT® 4.0 registry key. The default permissions could allow a malicious user who can interactively log onto a Windows NT 4.0 machine to compromise the cryptographic keys of other users who subsequently log onto the same machine.

Frequently asked questions regarding this vulnerability and the patch can be found at http://www.microsoft.com/technet/security/bulletin/fq00-024.mspx

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General Information

Issue

This vulnerability involves a registry key used by the CryptoAPI Base CSPs to specify the driver DLL for a hardware accelerator. By design, such a DLL would have access to users' public and private keys. Although only administrators should have permission to add such a DLL, the permissions on the key actually would allow any user who could interactively log onto the machine to do so. By writing a bogus DLL and installing it, a malicious user could compromise the keys of other users who subsequently used the machine.

The machines primarily at risk would be workstations and terminal servers. If normal security recommendations are followed, normal users will not be allowed to interactively log onto domain controllers, web servers, database servers, ERP servers, and other security-critical machines. Windows NT auditing could be used to determine who changed the key's value. A tool is available that resets the permissions on the affected key to the correct default values. In addition, it incorporates the functionality of the tool provided in Microsoft Security Bulletin MS00-008.

Affected Software Versions

•	Microsoft Windows NT 4.0 Workstation
•	Microsoft Windows NT 4.0 Server
•	Microsoft Windows NT 4.0 Server, Enterprise Edition
•	Microsoft Windows NT 4.0 Server, Terminal Server Edition NOTE: Windows 2000 is not affected by this vulnerability.

Vulnerability Identifier: CAN-2000-0259

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Patch Availability

•

X86: http://www.microsoft.com/downloads/details.aspx?FamilyId=AB792154-6BBD-4D27-9C87-8C7689BD908F&displaylang=en

•

Alpha: http://www.microsoft.com/downloads/details.aspx?FamilyId=AECBDFA7-D641-4FE7-A799-9D5C4F103DB2&displaylang=en

Note: This tool also covers the vulnerability described in MS00-008.

Note: Additional security patches are available at the Microsoft Download Center

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More Information

Please see the following references for more information related to this issue.

•	Frequently Asked Questions: Microsoft Security Bulletin MS00-024
•	Microsoft Knowledge Base (KB) article 259496, Incorrect Registry Permission Could Allow Key Compromise, http://support.microsoft.com/default.aspx?scid=kb;en-us;259496
•	Microsoft TechNet Security web site, http://www.microsoft.com/technet/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.

Acknowledgments

Microsoft thanks Sergio Tabanelli and Banca Nazionale del Lavoro for reporting this vulnerability to us and working with us to protect customers.

Revisions

•	April 12, 2000: Bulletin Created.

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