An ISA Server 2006 Web Proxy client receives error code 502 when a user tries to visit certain Web sites

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SYMPTOMS

Consider the following scenario. A computer is configured as a Microsoft Internet Security and Acceleration (ISA) Server 2006 Web Proxy client. A user on this client computer tries to visit certain Web sites. In this scenario, the user receives the following error page:

The page cannot be displayed

There is a problem with the page you are trying to reach and it cannot be displayed.

Technical Information (for support personnel)
Error Code: 502 Proxy Error.
The HTTP message includes an unsupported header or an unsupported combination of headers. (12156)

Additionally, you experience the following symptoms:

If you perform a network trace of the HTTP traffic, you capture an HTTP header that begins with a space.
If you use ISA Server Monitoring to log the HTTP traffic, the following error information is logged:
ERROR:Multi line header - unsupported.

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CAUSE

This problem occurs if a Web server response contains an HTTP header that begins with a space or with a TAB character.

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RESOLUTION

A hotfix is available for computers that are running ISA Server 2006. To resolve this problem, install the hotfix that is described in the following Microsoft Knowledge Base article:

935882 (http://support.microsoft.com/kb/935882/ ) Description of the ISA Server 2006 hotfix package that is dated April 19, 2007

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Hotfix installation information

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

322756 (http://support.microsoft.com/kb/322756/ ) How to back up and restore the registry in Windows

By default, this hotfix provides is not automatically enabled. To enable this hotfix, start Registry Editor, and then configure the following registry entry:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\RAT\Stingray\Debug\Web Filters

Value name: DROP_CONTINUATION_LINES
Value type: REG_DWORD
Value data: 1

You can also configure this registry entry by using a .reg file. To do this, paste the following code into a text file that has a .reg file-name extension.

Windows Registry Editor Version 5.00
 
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\RAT\Stingray\Debug\Web Filters] 
"DROP_CONTINUATION_LINES"=dword:00000001

After you configure this registry entry, ISA Server 2006 removes any HTTP headers that begin with a space or with a TAB character. Then, ISA Server 2006 forwards the response to the client computer.

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STATUS

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

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MORE INFORMATION

Trace information

When this problem occurs, you may capture trace information that resembles the following:

Http: Response, HTTP/1.1, Status Code = 200
    ProtocolVersion: HTTP/1.1
    StatusCode: 200, Ok
    Reason: OK
    Server:  Microsoft-IIS/5.0
    Date:  <date> <time>
     :  ASP.NET                   <---------------- This header begins with a space
    XPoweredBy:  ASP.NET
    Set-Cookie:  SITESERVER=ID=<ID string>; expires=<day>, <date> <time> GMT; path=/; domain=.example.com
    Expires:  <day>, <date> <time> GMT
    ContentLength:  73313
    ContentType:  text/html
    Set-Cookie:  ASPSESSIONIDACDSCSDD=LBJHCIECIJKLACBEOEOBMHAC; path=/
    Cache-control:  private
    HeaderEnd: CRLF

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