The "401 Authentication Required" response that is sent by a Web site is dropped when you use ISA Server 2004 or ISA Server 2006 as a Web proxy


Symptoms


Consider the following scenario:
  • You use Microsoft Internet Security and Acceleration (ISA) Server 2004 or ISA Server 2006 as a Web proxy to access a Web site.
  • You perform a POST operation on the Web site.
  • The Web site sends a "401 Authentication Required" response to the client.
However, ISA Server drops the "401 Authentication Required" response instead of forwarding the response to the client. This problem may cause the Web access attempt to fail. For example, when you try to upload a large file to the Web site, the upload operation may time out.

Resolution


To resolve this problem, follow these steps:
  1. If you are running ISA Server 2004, apply the hotfix package that is described in the following Microsoft Knowledge Base article:
    940709 Description of the ISA Server 2004 hotfix package: July 25, 2007


    If you are running ISA Server 2006, apply the last ISA Server service pack. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

    954258 How to obtain the latest Internet Security and Acceleration (ISA) Server 2006 service pack

  2. Start Notepad.
  3. Copy the following code, and then paste it into Notepad.
    Const SE_VPS_GUID = "{143F5698-103B-12D4-FF34-1F34767DEabc}"
    Const SE_VPS_NAME = "AllowPrematureServerResponse"
    Const SE_VPS_VALUE = true

    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
  4. Save the file as a Microsoft Visual Basic script file by using the .vbs file name extension. For example, use the following name to save the file:
    AllowPrematureServerResponse.vbs
  5. Start a command prompt, change to the location at which you saved the AllowPrematureServerResponse.vbs file, and then run the following command:
    cscript AllowPrematureServerResponse.vbs

Status


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

More Information


For more information about how to install ISA Server hotfixes and updates, click the following article number to view the article in the Microsoft Knowledge Base:
885957 How to install ISA Server hotfixes and updates