Authentication fails when client computers use Internet Explorer 7 to authenticate with an upstream ISA Server computer through a downstream ISA Server computer that does not require authentication

Consider the following scenario:

• You configure an upstream Microsoft Internet Security and Acceleration (ISA) Server computer that requires authentication.
• You configure a downstream ISA Server computer that does not require authentication.
• Client computers that are connected to the downstream ISA Server computer are running Windows Internet Explorer 7.

In this scenario, the client computers cannot authenticate with the upstream ISA Server computer.

Client computers that are running Internet Explorer 7 obtain a Kerberos ticket that is valid for authentication with the downstream server. However, this Kerberos ticket is not validated by the authenticating upstream ISA Server computer.

Specifically, when the upstream ISA Server computer requests authentication, the client computer obtains a Kerberos ticket for the downstream server. This Kerberos ticket is valid for authentication with the downstream ISA Server computer. This ticket cannot be used to authenticate with the upstream ISA Server computer. When the Kerberos ticket is presented to the upstream ISA Server computer, the upstream ISA Server computer cannot validate the ticket. Therefore, authentication fails.

Notes

• The downstream ISA Server computer is the proxy server with which the client computer is communicating.
• Internet Explorer 7 includes support for Kerberos authentication against proxy servers.

NTLM authentication is the alternative authentication method for instances when Kerberos authentication fails. However, the client computer does not use NTLM authentication because the client computer has successfully obtained a Kerberos ticket for the proxy server.

Hotfix information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

Prerequisites

The computer must be running ISA Server 2004 Service Pack 2 (SP2) to apply the ISA Server 2004 version of this hotfix.

Restart requirement

After you apply this hotfix, the hotfix will restart ISA Server services.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

File information

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.

ISA Server 2006

ISA Server 2004, Enterprise Edition

ISA Server 2004, Standard Edition

Post-hotfix installation information

After you apply this hotfix, you must run the following Microsoft Visual Basic script to configure the upstream ISA Server computer to return NTLM authentication headers only when Windows Integrated authentication is used.

Note This is a global setting for the ISA server. This script will change the authentication headers that are returned for both forward and reverse proxy requests (web proxy and web publishing listeners). To run this script, follow these steps:

1. Click Start, point to Programs, point to Accessories, and then click Notepad.
2. Copy the following code, and then paste it into Notepad.
   

   ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
   '
   ' Copyright (c) Microsoft Corporation. All rights reserved.
   ' THIS CODE IS MADE AVAILABLE AS IS, WITHOUT WARRANTY OF ANY KIND. THE ENTIRE
   ' RISK OF THE USE OR THE RESULTS FROM THE USE OF THIS CODE REMAINS WITH THE
   ' USER. USE AND REDISTRIBUTION OF THIS CODE, WITH OR WITHOUT MODIFICATION, IS
   ' HEREBY PERMITTED.
   ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
   
   ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
   ' This script sets authentication schemes that ISA will return for Integrated authentication.
   ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
   
   const USE_ONLY_NTLM_FOR_WINDOWS_AUTH_default = 0 ' Use Negotiate and Kerberos, too.
   const USE_ONLY_NTLM_FOR_WINDOWS_AUTH_Always  = 1
   
   Const SE_VPS_GUID = "{143F5698-103B-12D4-FF34-1F34767DEabc}"
   Const SE_VPS_NAME = "UseOnlyNTLMForWindowsAuth"
   Const SE_VPS_VALUE = 1
   
   Sub SetValue()
   
       ' Create the root object.
       Dim root  ' The FPCLib.FPC root object
       Set root = CreateObject("FPC.Root")
   
       'Declare the other objects that are needed.
       Dim array       ' An FPCArray object
       Dim VendorSets  ' An FPCVendorParametersSets collection
       Dim VendorSet   ' An FPCVendorParametersSet object
   
       ' Get references to the array object
       ' and to the network rules collection.
       Set array = root.GetContainingArray
       Set VendorSets = array.VendorParametersSets
   
       On Error Resume Next
       Set VendorSet = VendorSets.Item( SE_VPS_GUID )
   
       If Err.Number <> 0 Then
           Err.Clear
   
           ' Add the item.
           Set VendorSet = VendorSets.Add( SE_VPS_GUID )
           CheckError
           WScript.Echo "New VendorSet added... " & VendorSet.Name
   
       Else
           WScript.Echo "Existing VendorSet found... value- " &  VendorSet.Value(SE_VPS_NAME)
       End If
   
       if VendorSet.Value(SE_VPS_NAME) <> SE_VPS_VALUE Then
   
           Err.Clear
           VendorSet.Value(SE_VPS_NAME) = SE_VPS_VALUE
   
           If Err.Number <> 0 Then
               CheckError
           Else
               VendorSets.Save false, true
               CheckError
   
               If Err.Number = 0 Then
                   WScript.Echo "Done with " & SE_VPS_NAME & ", saved!"
               End If
           End If
       Else
           WScript.Echo "Done with " & SE_VPS_NAME & ", no change!"
       End If
   
   End Sub
   
   Sub CheckError()
   
       If Err.Number <> 0 Then
           WScript.Echo "An error occurred: 0x" & Hex(Err.Number) & " " & Err.Description
           Err.Clear
       End If
   
   End Sub
   
   SetValue
   

3. Save this Notepad file as UseOnlyNTLMforWindowsAuth.vbs.
4. Double-click the .vbs file to run the script.

Note To revert to the default authentication setting, change the SE_VPS_VALUE to 0, and then rerun the script.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

An additional problem may occur after you enable this hotfix on the upstream server. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base: