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FIX: Error message occurs when you try to access a web server that requires a client certificate if HTTPS inspection is enabled in Forefront TMG 2010: "Error Code: 502 Proxy Error. The message received was unexpected or badly formatted. (-2146893018)"

SYMPTOMS
Consider the following scenario:
  • You enable HTTPS inspection in Microsoft Forefront Threat Management Gateway (TMG) 2010.
  • You try to access a web server that requires a client certificate from the client.
  • You type the server name of this web server in the destination exception list for HTTPS inspection.
In this scenario, you cannot access the web server and receive the following error message:
Error Code: 502 Proxy Error. The message received was unexpected or badly formatted. (-2146893018)

CAUSE
This issue occurs because Forefront TMG 2010 sends an empty client certificate to the web server during the initial SSL handshake. Some web servers like IIS web servers accept and renegotiate the client certificate when a request that contains an empty client certificate is sent. However, other web servers may return an SSL error when the web server receives the empty client certificate. This behavior causes Forefront TMG not to correctly handle the server error.
RESOLUTION
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, but they will not modify these examples to provide added functionality or construct procedures to meet your specific requirements.

To resolve this problem, follow these steps:
  1. Install Forefront Threat Management Gateway 2010 Service Pack 1.
    For more information about how to obtain Forefront Threat Management Gateway 2010 Service Pack 1, click the following article number to view the article in the Microsoft Knowledge Base:
    981324 List of problems that are fixed in Forefront Threat Management Gateway 2010 Service Pack 1
  2. On the Destination Exceptions tab of the HTTPS Outbound Inspection dialog box, select the No Validation option for the web server.

    Note When the No Validation option is set, Forefront TMG 2010 cannot retrieve and validate the server certificate of Forefront TMG 2010.
  3. Start Notepad, and then copy the following script into a Notepad file.
    Const SE_VPS_GUID = "{143F5698-103B-12D4-FF34-1F34767DEabc}"Const SE_VPS_NAME = "EnableHotfix982550"Const SE_VPS_VALUE = trueSub 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 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 IfEnd SubSub CheckError()    If Err.Number <> 0 Then        WScript.Echo "An error occurred: 0x" & Hex(Err.Number) & " " & Err.Description        Err.Clear    End IfEnd SubSetValue
  4. Save the file as a Microsoft Visual Basic script file by using the .vbs file name extension. For example, save the file by using the following name:
    EnableHotfix982550.vbs
  5. Double-click the .vbs file to run it.
STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
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
Properties

Article ID: 982550 - Last Review: 06/22/2010 09:42:00 - Revision: 2.0

Microsoft Forefront Threat Management Gateway 2010 Enterprise, Microsoft Forefront Threat Management Gateway 2010 Standard

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