Date: 05 April 2002
Click here for printable version
Click here for PGP verifiable version
-----BEGIN PGP SIGNED MESSAGE-----
AUSCERT External Security Bulletin Redistribution
ESB-2002.165 -- Microsoft Security Bulletin MS02-016
Q318593: Opening Group Policy Files for Exclusive Read
Blocks Policy Application
5 April 2002
AusCERT Security Bulletin Summary
Product: Group Policy
Operating System: Windows 2000 Server
Windows 2000 Advanced Server
Windows 2000 Datacenter Server
Impact: Increased Privileges
Access Required: Existing Account
- --------------------------BEGIN INCLUDED TEXT--------------------
Title: Q318593: Opening Group Policy Files for Exclusive Read
Blocks Policy Application
Date: 04 April 2002
Microsoft Windows 2000 Server
Microsoft Windows 2000 Advanced Server
Microsoft Windows 2000 Datacenter Server
Impact: Attacker could block application of Group Policy.
Recommendation: Administrators should consider applying the patch to
Max Risk: Moderate
Microsoft encourages customers to review the Security Bulletin at:
Group Policy in Windows 2000 is implemented by storing data in the
Active Directory and the system volume on the domain controller. This
storage location is called the Group Policy Object (GPO). When a
machine or user logs onto the domain, it reads the GPO and applies
the settings it contains. Most of these settings are also refreshed
by default every 90 minutes. However, like most operating systems,
Windows 2000 provides several types of read access, including
exclusive-read, and this could enable an attacker to lock the Group
Policy files, thereby allowing a user to prevent Group Policy from
being applied for all users affected by the GPO.
An attacker would likely exploit the vulnerability by first logging
onto the domain normally, and then opening the Group Policy files
with exclusive read access. She could then log onto the network a
second time. Because the policy files would be locked, the second
logon would occur without Group Policy being applied. The result
would be that, although all previous Group Policy settings on the
second machine would remain in force, any new policy settings would
not be applied. The attacker's second session would take place using
what policy settings had most recently been applied.
The effect wouldn't be limited only to the attacker. Any other user
who happened to log onto the network while the Group Policy files
were locked would also do so without new policy settings being
applied. However, users who weren't involved in the attack might be
unable to determine that policy had been blocked. Group Policy
application is a transparent process, so such a user would likely be
unaware that the intended policy settings have not been applied.
The vulnerability would enable an attacker to block the application
of new Group Policy settings, but any settings that had been applied
during previous logons would remain in force.
The vulnerability could only be exploited by a user who had a bona
fide userid and password on the network.
The specific gain for the attacker would depend on the extent to
which the administrator had customized Group Policy on the domain.
The vulnerability would provide no way for an attacker to change
Group Policy, or to gain user group memberships.
An administrator could determine the attacker's identity by using
the Shared Folders MMC snap-in to view the userid of the person who
had the policy files open.
- - Internet Systems: Low
- - Intranet Systems: Moderate
- - Client Systems: None
- A patch is available to fix this vulnerability. Please read the
Security Bulletin at
for information on obtaining this patch.
- --------------------------END INCLUDED TEXT--------------------
You have received this e-mail bulletin as a result of your organisation's
registration with AusCERT. The mailing list you are subscribed to is
maintained within your organisation, so if you do not wish to continue
receiving these bulletins you should contact your local IT manager. If
you do not know who that is, please send an email to email@example.com
and we will forward your request to the appropriate person.
This security bulletin is provided as a service to AusCERT's members. As
AusCERT did not write the document quoted above, AusCERT has had no control
over its content. 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.
NOTE: This is only the original release of the security bulletin. It may
not be updated when updates to the original are made. If downloading at
a later date, it is recommended that the bulletin is retrieved directly
from the original authors to ensure that the information is still current.
Contact information for the authors of the original document is included
in the Security Bulletin above. 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
Internet Email: firstname.lastname@example.org
Facsimile: (07) 3365 7031
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.
-----BEGIN PGP SIGNATURE-----
-----END PGP SIGNATURE-----