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AUSCERT External Security Bulletin Redistribution
ESB-97.093 -- CIAC Bulletin H-84
Windows NT NtOpenProcessToken Vulnerability
24 July 1997
The U.S. Department of Energy Computer Incident Advisory Capability has
released the following advisory concerning a vulnerability in a Microsoft
Windows NT operating system kernel routine. This vulnerability may allow
local users to gain administrator privileges.
The following security bulletin is provided as a service to AUSCERT's
members. As AUSCERT did not write this document, AUSCERT has had no
control over its content. As such, the decision to use any or all of this
information is the responsibility of each user or organisation, and should
be done so in accordance with site policies and procedures.
Contact information for CIAC is included in the Security Bulletin
below. If you have any questions or need further information, please
contact them directly.
Previous advisories and external security bulletins can be retrieved from:
If you believe that your system has been compromised, contact AUSCERT or your
representative in FIRST (Forum of Incident Response and Security Teams).
Internet Email: firstname.lastname@example.org
Facsimile: (07) 3365 4477
Telephone: (07) 3365 4417 (International: +61 7 3365 4417)
AUSCERT personnel answer during Queensland business hours
which are GMT+10:00 (AEST).
On call after hours for emergencies.
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[ For Public Release ]
The U.S. Department of Energy
Computer Incident Advisory Capability
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Windows NT NtOpenProcessToken Vulnerability
July 22, 1997 18:00 GMT Number H-84
PROBLEM: A vulnerability exists in a Microsoft Windows NT operating
system kernel routine.
PLATFORM: Windows NT Workstation and Server 4.0.
DAMAGE: Exploit allows local users to gain Administrator privileges.
SOLUTION: Apply the Microsoft patch and follow the policy guidelines
VULNERABILITY Exploit is widely available, but attack is only successfully
ASSESSMENT: executed locally.
A vulnerability in Microsoft Windows NT 4.0 allows a user to locally execute a
utility to gain administrator privileges. The utility is successfully
executed from most local user accounts, regardless of the permissions. An
exception to this is the Guest account. Because the attacker must have a
valid account and physical access to the system for this attack to be
successful, the attacker is most likely to be an "insider".
The utility works by adding the user (or attacker) to the Administrators'
Group. The Administrators group is usually designed such that its members can
modify the registry, including adding and deleting users, as well as perform
other security functions (changing passwords, permissions, etc.). This group
and any other group or user who has the "Debug Programs" privilege (used for
testing and debugging programs) will always be able to successfully execute
this utility, as well as many other utilities with security risks.
In order to mitigate this and similar attacks, CIAC recommends that the
following four configuration controls be applied:
1. Apply the Microsoft hotfix located below. CIAC highly recommends that
Service Pack 3 is installed first.
Microsoft's Debug Right Vulnerability hotfix location for the U.S. version of
2. Limit debug rights to those trusted users who must conduct testing or
debugging functions on the system. In general, very few users need the
ability to test and debug systems. Privileges should be granted on an
individual case by case basis. If possible, avoid granting entire groups this
privilege. Once the Microsoft hotfix described in item 1 above is applied,
this specific attack will only work if executed from accounts which have
legitimately been granted the debug right, or are already a member of the
Administrators' Group. To check or change who has the "Debug Programs" Right:
1. Log in as an administrator (or equivalent privileges)on either Windows NT
Workstation or Server (process is similar for both).
2. Open "User Manager".
3. Choose "Policies", then "User Rights".
4. Check the "Show Advanced User Rights" box. ("Debug Programs" is an
Advanced User Right).
5. Choose the "Debug Programs" Right, and Add or Remove users/groups as
3. Prohibit most users from having physical access to the NT server
consoles. This can be accomplished by setting the "Log on Locally" right to
only a few trusted administrators. In addition, servers should physically
reside in a location that is secured, and physical access is controlled, such
as a locked computer room or (well-ventilated) closet.
4. As with any operating system, limit the number of users granted
administrator privileges, and limit the number of users who have access to the
Administrator account. Make sure the activities of these accounts
(especially Registry changes) are audited to provide a traceable record of
events. Users should only use their Administrator accounts when necessary.
They should also have a working account not in the Administrators' group to
use when not conducting administrator responsibilities. Permissions should be
minimally granted, so that users have just enough privileges to accomplish
their tasks, and are provided limited access, especially to system files.
CIAC would like to thank Karan Khanna and Microsoft for their contributions
in this bulletin.
CIAC, the Computer Incident Advisory Capability, is the computer
security incident response team for the U.S. Department of Energy
(DOE) and the emergency backup response team for the National
Institutes of Health (NIH). CIAC is located at the Lawrence Livermore
National Laboratory in Livermore, California. CIAC is also a founding
member of FIRST, the Forum of Incident Response and Security Teams, a
global organization established to foster cooperation and coordination
among computer security teams worldwide.
CIAC services are available to DOE, DOE contractors, and the NIH. CIAC
can be contacted at:
Voice: +1 510-422-8193
FAX: +1 510-423-8002
STU-III: +1 510-423-2604
For emergencies and off-hour assistance, DOE, DOE contractor sites,
and the NIH may contact CIAC 24-hours a day. During off hours (5PM -
8AM PST), call the CIAC voice number 510-422-8193 and leave a message,
or call 800-759-7243 (800-SKY-PAGE) to send a Sky Page. CIAC has two
Sky Page PIN numbers, the primary PIN number, 8550070, is for the CIAC
duty person, and the secondary PIN number, 8550074 is for the CIAC
Previous CIAC notices, anti-virus software, and other information are
available from the CIAC Computer Security Archive.
World Wide Web: http://ciac.llnl.gov/
Anonymous FTP: ciac.llnl.gov (220.127.116.11)
Modem access: +1 (510) 423-4753 (28.8K baud)
+1 (510) 423-3331 (28.8K baud)
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This document was prepared as an account of work sponsored by an
agency of the United States Government. Neither the United States
Government nor the University of California nor any of their
employees, makes any warranty, express or implied, or assumes any
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H-78: ICMP vulnerability in Windows 95 and NT 4.0
H-79: Vellum 3D CD-ROM contains Mac MBDF Virus
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H-81: HP-UX swinstall command in SD-UX Vulnerability
H-82: Lynx Temporary Files & Downloading Vulnerabilities
H-83: Solaris ping Vulnerability
H-84: Windows NT NtOpenProcessToken Vulnerability
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