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Problems with Kerberos authentication when a user belongs to many groups
Article ID: 327825 - View products that this article applies to.
This article was previously published under Q327825
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When a user belongs to many groups, that user may have problems with authentication or with Group Policy settings. The following Microsoft Knowledge Base articles describe these symptoms in more detail:
(http://support.microsoft.com/kb/269643/ )Internet Explorer Kerberos authentication does not work because of an insufficient buffer connecting to IIS
(http://support.microsoft.com/kb/280380/ )Buffer overflow exploit possible with extended stored procedures
2020943The resolution that is described in these articles instructs you to modify the MaxTokenSize registry value. An improvement was made to this resolution. If you use the hotfix that is described in this article, you may not have to edit the default MaxTokenSize value.
(http://support.microsoft.com/kb/2020943/ )"HTTP 400 - Bad Request (Request Header too long)" error in Internet Information Services (IIS)
The hotfix that is described in this article supersedes the hotfixes that are described in Microsoft Knowledge Base articles that are listed in this section.
The user cannot authenticate because the Kerberos token that is generated during authentication attempts has a fixed maximum size. Transports such as remote procedure call (RPC) and HTTP rely on the MaxTokenSize value when they allocate buffers for authentication. In Windows 2000 (the original release version), the MaxTokenSize value is 8,000 bytes. In Windows 2000 Service Pack 2 (SP2) and Windows Server 2003, the MaxTokenSize value is 12,000 bytes.
Kerberos uses the Privilege Attribute Certificate (PAC) field of the Kerberos packet to transport Active Directory Group membership. Starting with Windows Server 2012, this also applies to the Active Directory Claims information (Dynamic Access Control) field. If there are many group memberships for the user, and if there are many claims for the user or the device that is being used, these fields can occupy lots of space in the packet.
If a user is a member of more than 120 groups, the buffer that is determined by the MaxTokenSize value is not large enough. Therefore, users cannot authenticate, and they may receive an "out of memory" error message. Before you apply the hotfix that is described in this article, every group that is added to a user account increases this buffer by 40 bytes.
Note In many scenarios, Windows NTLM authentication works as expected. You may not see the Kerberos authentication problem without analysis. However, scenarios in which Group Policy settings are applied may not work as expected.
Important To resolve this problem, you must set the MaxTokenSize registry value for all the computers that are involved in the Kerberos authentication process. This includes the SQL Server clients. (That is, the registry key has to be set on each computer that is involved in the request/response flow. Therefore, if there is a SQL Server client on which a web application relies, or if the user’s token has to be passed to a backend SQL Server database, the registry key has to be set on the SQL Server client computer, the SQL Server database computer, and also the client computer that is running Internet Explorer, the web server running that is running IIS, and so on.)
Note The following Windows versions include a fix for this problem:
Service pack informationTo resolve this problem, obtain the latest service pack for Microsoft Windows 2000. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/260910/ )How to obtain the latest Windows 2000 service pack
Hotfix informationA supported hotfix is now available from Microsoft. However, it is intended to correct only the problem that is described in this article. Apply it only to systems that are experiencing this specific problem. This hotfix may receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next Windows 2000 service pack that contains this hotfix.
To resolve this problem immediately, contact Microsoft Customer Support Services to obtain the hotfix. For a complete list of Microsoft Customer Support Services telephone numbers and information about support costs, go to the following Microsoft website:
http://support.microsoft.com/contactus/?ws=supportNote In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question. The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section. This problem was first corrected in Microsoft Windows 2000 Service Pack 4.
Token Size Calculation Windows 2000 to Windows Server 2008 R2If you use the hotfix that is described in this article, you do not have to modify the MaxTokenSize registry value in most cases. However, there are some scenarios in which you have to modify the MaxTokenSize registry value after you apply this hotfix. After you apply this hotfix to all the domain controllers, use the following formula to determine whether you have to modify the MaxTokenSize value:
TokenSize = 1200 + 40d + 8sThis formula uses the following values:
When to set the registry entryIf the token size that you calculate by using this formula is less than 12,000 bytes (the default size), you do not have to modify the MaxTokenSize registry value on domain clients. If the value is more than 12,000 bytes, see the following Microsoft Knowledge Base article for a description of how to adjust the MaxTokenSize registry value:
(http://support.microsoft.com/kb/263693/ )Group Policy may not be applied to users belonging to many groups
328889 Users who are members of more than 1,015 groups may fail logon authentication
Therefore, a MaxTokenSize value for more than 1015 effective SIDs is not useful. In the following formula:
MaxTokenSize = 1200 + 40d + 8s40d means that you have 40 bytes for a Domain Local Group SID. 8s means 8 bytes for a Domain Global/Universal Group SID.
Therefore, if you have a MaxTokenSize value of 0x0000FFFF (64K), you may be able to buffer approximately 1600 Domain Local Group SIDs or approximately 8000 Domain Global/Universal Group SIDs. If you use "trusted for delegation" accounts, the buffer requirement for each SID may be doubled. In these scenarios, you can only store approximately 800 Domain Local Group SIDs when a MaxTokenSize value of 64K is used. However, having only Domain Local Group SIDs is not a typical scenario. A value of 64K should be sufficient even for delegation scenarios.
Windows Server 2012 changesWindows Server 2012 introduced the following changes to the considerations about this buffer:
For more information about Windows Server 2012 changes, go to the following Microsoft TechNet website:
Examples of problems when the ticket size is exceededFor more information, click the following article numbers to view the articles in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/277741/ )Internet Explorer logon fails due to an insufficient buffer for Kerberos
(http://support.microsoft.com/kb/313661/ )Error message: "Timeout expired" occurs when you connect to SQL Server over TCP/IP and the Kerberos MaxTokenSize is greater than 0xFFFF
Because you may have cross-domain logon scenarios in your forest, the value should be set forest-wide on all Windows-based systems. Therefore, we recommend that the maximum value for the MaxTokenSize value be 64K.
Important On SQL Server clients, you may receive the following error message when this problem occurs:
To resolve this problem, you must set the MaxTokenSize registry value for all the computers that are involved in the Kerberos authentication process. This includes the SQL Server clients.
Cannot generate SSPI context
Article ID: 327825 - Last Review: February 20, 2013 - Revision: 18.0