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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"

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 IfEnd SubSub CheckError()    If Err.Number <> 0 Then        WScript.Echo "An error occurred: 0x" & Hex(Err.Number) & " " & Err.Description        Err.Clear    End IfEnd SubSetValue
  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: 03/24/2009 17:56:33 - Revision: 2.0

  • 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
  • kberrmsg kbfirewall kbtshoot kbfix kbbug kbprb KB920913
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