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Q240073: Privilege Violation When Creating a Pipe Instance in NPFS

Article: Q240073
Product(s): Microsoft Windows NT
Version(s): winnt:4.0
Operating System(s): 
Keyword(s): kbWinNT4sp6fix
Last Modified: 20-MAY-2002

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The information in this article applies to:

- Microsoft Windows NT Server version 4.0, Terminal Server Edition 
- Microsoft Windows NT Server version 4.0 
- Microsoft Windows NT Workstation version 4.0 
- Microsoft Windows NT Server, Enterprise Edition version 4.0 
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SYMPTOMS
========

When a client uses the recommended FILE_GENERIC_WRITE access type to open a
named pipe to a server using the Microsoft Windows NT 4.0 Named Pipes File
System (NPFS), it is possible for the client, regardless of permissions, to
create an instance of a server pipe and wait for a privileged user to connect in
order to impersonate them on that instance. This privilege violation poses a C2
security risk.

CAUSE
=====

This behavior also occurs because NPFS does not verify that the user has the
needed permissions in the Access Control List (ACL) and access type in the
Discretionary Access Control List (DACL). Another factor contributing to this
situation is that named pipes which were not created with an explicit security
descriptor receive the NULL security descriptor and allows unprivileged
processes to obtain handles to named pipes on a server.

RESOLUTION
==========

Windows NT Server or Workstation 4.0
------------------------------------

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or the
individual software update. For information on obtaining the latest service
pack, please go to:

- http://www.microsoft.com/Windows/ServicePacks/

-or-

- Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack

For information on obtaining the individual software update, contact Microsoft
Product Support Services. For a complete list of Microsoft Product Support
Services phone numbers and information on support costs, please go to the
following address on the World Wide Web:

  http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS


Windows NT Server 4.0, Terminal Server Edition
----------------------------------------------

To resolve this problem, obtain the latest service pack for Windows NT Server
4.0, Terminal Server Edition. For additional information, please see the
following article in the Microsoft Knowledge Base:

  Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack


STATUS
======

Microsoft has confirmed this to be a problem in Windows NT 4.0 and Windows NT
Server 4.0, Terminal Server Edition.

This problem was first corrected in Windows NT Server 4.0 Service Pack 6 and
Windows NT Server 4.0, Terminal Server Edition Service Pack 6.

MORE INFORMATION
================

Without the application of Windows NT 4.0 Service Pack 6, a server running
Windows NT 4.0 cannot stop clients from creating an instance of a named pipe
because the instance bits from FILE_CREATE_PIPE_INSTANCE overlap with
FILE_APPEND_DATA in the GENERIC_WRITE access type. So long as a client has
FILE_GENERIC_WRITE access to a pipe, they can create an instance and acquire
unauthorized access. NPFS can then check for permissions and access types, and a
default security descriptor is added to the I/O Manager that does not allow
unprivileged access.

An application, however, can protect itself against being instanced in this
situation by denying all access to the pipe (the Dynamic Host Control Protocol
(DHCP) client is an example of an application that denies all access).

Within the Security Descriptor, (a special data structure containing security
information for an object), the DACL identifies users and group Security
Identifiers (SIDs) that are to be granted or denied access for an object, and
the System Access Control List (SACL) controls the auditing message the
operating system generates. Both the DACL and the SACL contain ACE elements,
which specify the users and groups with their individual permissions. The SID,
ACL, DACL, and SACL are components that play a role in determining how well a
computer complies with the U.S. Department of Defense C2security specification.

For more information on the requirements and characterisitcs of C2 security,
please visit the following Microsoft Web site:

http://www.microsoft.com/NTServer/security/exec/overview/C2Beyond.asp

Additional query words:

======================================================================
Keywords          : kbWinNT4sp6fix 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT400search kbWinNTSsearch kbWinNTSEntSearch kbWinNTSEnt400 kbWinNTS400search kbWinNTS400 kbNTTermServ400 kbNTTermServSearch
Version           : winnt:4.0
Issue type        : kbbug
Solution Type     : kbfix

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