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Article ID: 2622172 - Last Review: October 6, 2011 - Revision: 2.0

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Important This article contains information that shows you how to help lower security settings or how to turn off security features on a computer. You can make these changes to work around a specific problem. Before you make these changes, we recommend that you evaluate the risks that are associated with implementing this procedure in your particular environment. If you implement this procedure, take any appropriate additional steps to help protect the computer.

SYMPTOMS

Consider the following scenario:
  • You publish a webpage through Microsoft Internet Security and Acceleration (ISA) Server 2006 by using Forms-Based Authentication.
  • You access this webpage by using a URL that contains an escaped carriage return ("%0D") or a linefeed ("%0A") in the URL.

In this scenario, ISA Server 2006 blocks access to the URL. Additionally, the ISA Web Proxy logs show a result code of 12232 for the denied request.

Note Keep in mind that this result code can also be logged because of other issues and that the URL that is logged would have to be reviewed for %0a or %0d characters to determine whether this is the issue that you experienced.

CAUSE

This problem occurs because the Forms Based Authentication filter blocks known cross-site scripting and related attacks. In this case, the filter is blocking response splitting attacks that also include carriage returns or linefeeds. However, valid URLs can also include these characters. For example, the IBM Rational Clearquest application is known to use carriage returns or linefeeds in its URLs.

RESOLUTION

To resolve this problem, install the ISA Server 2006 hotfix rollup package that is described in the following Microsoft Knowledge Base article:
2616326  (http://support.microsoft.com/kb/2616326/ ) Description of the ISA Server 2006 hotfix package: September 2011

MORE INFORMATION

Warning This procedure may make a computer or a network more vulnerable to attack by malicious users or by malicious software such as viruses. We do not recommend this procedure but are providing this information so that you can implement this procedure at your own discretion. Use this procedure at your own risk.

The following script will disable the default behavior in ISA Server 2006 Service Pack 1 and enable the ISA Server to allow URLs that contain carriage returns (CR) or linefeeds (LF) in the URL address. To use this script, follow these steps.

ImportantNote Disabling this default behavior of ISA Server 2006 SP1 (in order to accommodate such applications) could also enable ISA Server to potentially allow the URLs that have been specifically crafted for “cross-site request forgery” attacks when ISA Server uses Form Based Authentication.
  1. Start Notepad.
  2. Paste the following script into a new document.
    Const SE_VPS_GUID = "{143F5698-103B-12D4-FF34-1F34767DEabc}"
    Const SE_VPS_NAME = "AllowNewlineInURL"
    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 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
  3. On the File menu, click Save As, and then save the file as AllowNewlineInURL.vbs.
  4. At a command prompt, type the following command, and then press Enter:
    cscript AllowNewlineInURL.vbs
To return to the default behavior in ISA Server 2006 Service Pack 1 to block URLs that might contain cross-site request forgery attacks when you use Form Based Authentication, follow these steps:
  1. Start Notepad, and then open the AllowNewlineInURL.vbs script.
  2. Locate the following line of code in the script.
    Const SE_VPS_VALUE = true
    
  3. Change the code to the following line:
    Const SE_VPS_VALUE = false
    
  4. On the File menu, click Save.
  5. At a command prompt, type the following command, and then press Enter:
    cscript AllowNewlineInURL.vbs

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  (http://support.microsoft.com/kb/824684/ ) Description of the standard terminology that is used to describe Microsoft software updates

APPLIES TO
  • Microsoft Internet Security and Acceleration Server 2006 Service Pack 1, when used with:
    • Microsoft Internet Security and Acceleration Server 2006 Enterprise Edition
    • Microsoft Internet Security and Acceleration Server 2006 Standard Edition
Keywords: 
kbfix kbqfe kbexpertiseadvanced kbsurveynew kbhotfixserver kbhotfixrollup KB2622172
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