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-----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 Vendor: Microsoft 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 Software: 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 domain controllers. Max Risk: Moderate Bulletin: MS02-016 Microsoft encourages customers to review the Security Bulletin at: http://www.microsoft.com/technet/security/bulletin/MS02-016.asp. - - - ---------------------------------------------------------------------- Issue: ====== 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. Mitigating Factors: =================== 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. Risk Rating: ============ - - Internet Systems: Low - - Intranet Systems: Moderate - - Client Systems: None Patch Availability: =================== - A patch is available to fix this vulnerability. Please read the Security Bulletin at http://www.microsoft.com/technet/security/bulletin/ms02-016.asp 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 auscert@auscert.org.au 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. 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Internet Email: auscert@auscert.org.au 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----- Version: 2.6.3i Charset: noconv Comment: ftp://ftp.auscert.org.au/pub/auscert/AUSCERT_PGP.key iQCVAwUBPK2rQCh9+71yA2DNAQG2XwP/fq9zCw9fma4aQuVd6c7M2obg6HaDFyOu dr6W6L25M45A0ElWRaVJiGwfjv0uzovNz4bGBXC7WpcqNifErNkO1rArvRaMTyfF 9HzVkKbeJaQE+hTBrKfjSEd0bkBQScMMQ4OnSA5Gz9IzpHP5D4ZJ9h4MTPIDtLmp jD3Zz+LxeNY= =FJcJ -----END PGP SIGNATURE-----