Microsoft Security Bulletin (MS00-024)
Tool Available for "OffloadModExpo Registry Permissions" Vulnerability
Originally Posted: April 12, 2000
Microsoft has released a tool that installs tighter permissions on a
Windows NT(r) 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
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.
NOTE: Additional security patches are available at the Microsoft
Please see the following references for more information related to
- Frequently Asked Questions: Microsoft Security Bulletin MS00-024,
- Microsoft Knowledge Base article Q259496 discusses this issue
and will be available soon.
- Microsoft TechNet Security web site,
Obtaining Support on this Issue
This is a fully supported patch. Information on contacting Microsoft
Technical Support is available at
Microsoft thanks Sergio Tabanelli and Banca Nazionale del Lavoro for
reporting this vulnerability to us and working with us to protect
- April 12, 2000: Bulletin Created.
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Last updated April 12, 2000