Error message in response to some HTTP requests on client computers that are running ISA Server 2004 or ISA Server 2006 as a proxy server: "400 Bad Request"

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Article ID: 920913 - View products that this article applies to.
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SYMPTOMS

On client computers that are configured to run Microsoft Internet Security and Acceleration (ISA) Server 2004 or ISA Server 2006 as a proxy server, you receive the following error message in response to some HTTP requests:
400 Bad Request
You experience this problem if the following conditions are true:
  • ISA Server is chained to an upstream proxy server.
  • The upstream proxy server is not running ISA Server.
  • The HTTP request does not contain a host header.

CAUSE

This problem occurs because ISA Server does not submit a host header to an upstream proxy server if the host header is missing from the client request. Therefore, the upstream proxy server may return the error message that is mentioned in the "Symptoms" section if the client request does not contain a host header.

By default, ISA Server sends HTTP requests as an HTTP 1.1 client. These kinds of client requests must include a host header. This requirement is specified in RFC 2616. Because ISA Server does not add a host header when it proxies the client request, the upstream proxy server may refuse the request.

Note This problem does not occur if the upstream proxy server is running ISA Server. ISA Server does not comply with RFC 2616 requirement to deny a HTTP 1.1 request that does not specify a host header.

RESOLUTION

To resolve this problem, obtain the latest ISA Server service pack.

For more information about how to obtain the latest ISA Server 2004 service pack, click the following article number to view the article in the Microsoft Knowledge Base:
891024 How to obtain the latest ISA Server 2004 service pack
For more information about how to obtain the latest ISA Server 2006 service pack, 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

STATUS

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

MORE INFORMATION

Microsoft provides programming examples for illustration only, without warranty either expressed or implied. This includes, but is not limited to, the implied warranties of merchantability or fitness for a particular purpose. This article assumes that you are familiar with the programming language that is being demonstrated and with the tools that are used to create and to debug procedures. Microsoft support engineers can help explain the functionality of a particular procedure. However, they will not modify these examples to provide extra functionality or construct procedures to meet your specific requirements.

After you install the service pack, you can restore the behavior of the release version of ISA Server. The original behavior is that ISA Server does not add a host header when it proxies an HTTP client request. To restore the original behavior in ISA Server, set the following vendor parameter:
REVERT_920913
To set the Revert_920913 vendor parameter, follow these steps:
  1. Start a text editor. For example, start Notepad.
  2. Paste the following script in the text editor, and then save the file by using a .vbs file name extension. For example, save the file as Revert_920913.vbs.
    Const SE_VPS_GUID = "{143F5698-103B-12D4-FF34-1F34767DEabc}"
    Const SE_VPS_VALUE = "Revert_920913"
    
    Sub SetValue()
    
        ' Create the root obect.
        Dim root  ' The FPCLib.FPC root object
        Set root = CreateObject("FPC.Root")
    
        'Declare the other objects needed.
        Dim array       ' An FPCArray object
        Dim VendorSets  ' An FPCVendorParametersSets collection
        Dim VendorSet   ' An FPCVendorParametersSet object
    
        ' Get references to the array object
        ' and 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_VALUE)
        End If
    
        if VendorSet.Value(SE_VPS_VALUE) <> true Then
    
            Err.Clear
            VendorSet.Value(SE_VPS_VALUE) = true
    
            If Err.Number <> 0 Then
                CheckError
            Else
                VendorSets.Save false, true
                CheckError
    
                If Err.Number = 0 Then
                    WScript.Echo "Done with " & SE_VPS_VALUE & ", saved!"
                End If
            End If
        Else
            WScript.Echo "Done with " & SE_VPS_VALUE & ", 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. Click Start, click Run, type cmd, and then click OK.
  4. At the command prompt, use the cd command to change to the directory where you saved the script.
  5. Type cscript scriptname, and then press ENTER. For example, type csript Revert_920913.vbs, and then press ENTER.

REFERENCES

For more information about how to install ISA Server 2004 hotfixes and updates, click the following article number to view the article in the Microsoft Knowledge Base:
885957 How to install ISA Server 2004 hotfixes and updates

Properties

Article ID: 920913 - Last Review: March 24, 2009 - Revision: 2.0
APPLIES TO
  • Microsoft Internet Security and Acceleration Server 2004 Enterprise Edition
  • Microsoft Internet Security and Acceleration Server 2004 Standard Edition
  • Microsoft Internet Security and Acceleration Server 2006 Enterprise Edition
  • Microsoft Internet Security and Acceleration Server 2006 Standard Edition
Keywords: 
kberrmsg kbfirewall kbtshoot kbfix kbbug kbprb KB920913

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