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FIX: Users are prompted to authenticate when the ReturnAuthRequiredIfAuthUserDenied property is set to True, and users are denied access by an "All Users" rule in a Forefront Threat Management Gateway 2010 environment

SYMPTOMS
When Microsoft Forefront Threat Management Gateway (TMG) 2010 denies a request for an authenticated user, the user receives a "502" error message to inform the user that he or she is denied access. Additionally, the user is not prompted to provide alternative credentials.

The ReturnAuthRequiredIfAuthUserDenied property can be set so that when an authenticated user is denied by the TMG policy, the user receives a "407 Proxy Authentication Required" message. This allows for the user to provide alternative credentials.

For more information about the ReturnAuthRequiredIfAuthUserDenied property, visit the following Microsoft Developer Network (MSDN) website:If an administrator creates a deny rule that applies to all users and sets the ReturnAuthRequiredIfAuthUserDenied property to True, a user who is denied by such a rule receives a "407 Proxy Authentication Required" message. This behavior occurs even though all users would be denied by this rule. This behavior may not be desired and could lead to unnecessary authentication prompts.
CAUSE
This behavior is by design. But this behavior may not be the desired behavior because an All Users deny rule blocks all users. Additionally, the prompts for alternative credentials does not resolve this issue.
RESOLUTION
To resolve this issue, install the software update that is described in the following Microsoft Knowledge Base article:
2517957 Software Update 1 Rollup 4 for Forefront Threat Management Gateway (TMG) 2010 Service Pack 1
After you apply this software update, run the script that is provided in the "More Information" section on one of the TMG array members to set the SkipReauthWhenNonDefaultRule property to True.
STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
MORE INFORMATION
This software update introduces a new property, SkipReauthWhenNonDefaultRule. This property provides new behavior. For example, consider the following scenarios.
Scenario 1

An administrator creates an All Users rule that denies access to an authenticated user, and the ReturnAuthRequiredIfAuthUserDenied property is set to True. In this scenario, if the SkipReauthWhenNonDefaultRule property is set to True, the user receives a "502" error message and is not prompted to provide alternative credentials.
Scenario 2

The default rule is applied, and the rule denies the request. Also, the ReturnAuthRequiredIfAuthUserDenied property is set to True. In this scenario, the user receives the "407 Proxy Authentication Required" message as expected.
After you apply this software update, run the following script on one of the TMG array members to set the SkipReauthWhenNonDefaultRule property to True. The default setting for the SkipReauthWhenNonDefaultRule property is False.

Note This script will only change the behavior when the ReturnAuthRequiredIfAuthUserDenied property is also set to True.
Const SE_VPS_GUID = "{143F5698-103B-12D4-FF34-1F34767DEabc}"Const SE_VPS_NAME = "SkipReauthWhenNonDefaultRule"Const SE_VPS_VALUE = trueSub SetValue()' Create the root obect.Dim root ' The FPCLib.FPC root objectSet root = CreateObject("FPC.Root")'Declare the other objects needed.Dim array ' An FPCArray objectDim VendorSets ' An FPCVendorParametersSets collectionDim VendorSet ' An FPCVendorParametersSet object' Get references to the array object' and the network rules collection.Set array = root.GetContainingArraySet VendorSets = array.VendorParametersSetsOn Error Resume NextSet VendorSet = VendorSets.Item( SE_VPS_GUID )If Err.Number <> 0 ThenErr.Clear' Add the itemSet VendorSet = VendorSets.Add( SE_VPS_GUID )CheckErrorWScript.Echo "New VendorSet added... " & VendorSet.NameElseWScript.Echo "Existing VendorSet found... value- " & VendorSet.Value(SE_VPS_NAME)End Ifif VendorSet.Value(SE_VPS_NAME) <> SE_VPS_VALUE ThenErr.ClearVendorSet.Value(SE_VPS_NAME) = SE_VPS_VALUEIf Err.Number <> 0 ThenCheckErrorElseVendorSets.Save false, trueCheckErrorIf Err.Number = 0 ThenWScript.Echo "Done with " & SE_VPS_NAME & ", saved!"End IfEnd IfElseWScript.Echo "Done with " & SE_VPS_NAME & ", no change!"End IfEnd SubSub CheckError()If Err.Number <> 0 ThenWScript.Echo "An error occurred: 0x" & Hex(Err.Number) & " " & Err.DescriptionErr.ClearEnd IfEnd SubSetValue
Note To revert to the default behavior, follow these steps:
  1. Locate the following line in the script:
    Const SE_VPS_VALUE = true
  2. Change the line in the script to the following:
    Const SE_VPS_VALUE = false
  3. Save the script, and rerun this script on one of the TMG Array members.
REFERENCES
For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:
824684 Description of the standard terminology that is used to describe Microsoft software updates
TMG authentication prompt 407 502 ReturnAuthRequiredIfAuthUserDenied
Properties

Article ID: 2518670 - Last Review: 06/15/2011 20:17:00 - Revision: 1.0

  • Microsoft Forefront Threat Management Gateway 2010 Service Pack 1
  • kbexpertiseinter kbbug kbsurveynew kbqfe kbfix KB2518670
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