FIX: Both sides of a TCP connection are closed when the client or remote application half-closes the TCP connection in a Forefront Threat Management Gateway 2010 environment

Symptoms

Consider the following scenario:
  • You have internal clients who are trying to access non-web-based application servers in a Microsoft Forefront Threat Management Gateway (TMG) 2010 environment.
  • The client traffic passes through an application filter in Forefront TMG that data-flows the traffic in user mode.
  • The client or the remote application server half-closes the TCP connection by sending a FIN/ACK packet. In doing this, the client or the remote application server expects the other half of the TCP connection to stay active.

In this scenario, you may notice that both sides of the TCP connection are closed immediately by the FIN/ACK packet.

Cause

When traffic is passed through a user-mode data flow, both sockets are closed after a FIN packet is received on one of them. This prevents Forefront TMG from supporting half-closed TCP connections as supported in the kernel-mode data flow.

Resolution

To resolve this issue, install the hotfix package that is described in the following Microsoft Knowledge Base article:
2649961 Rollup 1 for Forefront Threat Management Gateway (TMG) 2010 Service Pack 2
To enable this fix, follow these steps:
  1. Start Notepad. To do this, click Start, click Run, type notepad.exe in the Open box, and then click OK.
  2. Paste the following script to a new file in Notepad:
    set curArray = CreateObject("FPC.Root").GetContainingArray()
    Const SE_VPS_GUID = "{143F5698-103B-12D4-FF34-1F34767DEabc}"
    Const SE_VPS_NAME = "AllowHalfClosedConnection"
    Const SE_VPS_VALUE = True
    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 = curArray
    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
  3. Save the file as AllowHalfClosedConnection.vbs, and then exit Notepad.
  4. On a Forefront TMG server, open an administrative command prompt.
  5. Move to the location to which you saved the AllowHalfClosedConnection.vbs script, and then type the following command:
    Cscript.exe AllowHalfClosedConnection.vbs
This fix lets Forefront TMG enable half-closed TCP connections in user-mode data flows.

Note To change the functionality back to the default behavior, change the following line in the script by changing the value from True to False, and then run the script:
Const SE_VPS_VALUE = True

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: 2636183 - Last Review: Jan 11, 2012 - Revision: 1

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