Web content does not appear, or clients receive an "HTTP 502 Proxy Error" message when they try to access external Web sites with ISA Server 2000 (831140)

RESOLUTION

Hotfix information

A supported hotfix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Only apply it to systems that are experiencing this specific problem. This hotfix may receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next ISA Server 2000 server pack that contains this hotfix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the hotfix. For a complete list of Microsoft Product Support Services telephone numbers and information about support costs, visit the following Microsoft Web site:

http://support.microsoft.com/contactus/?ws=support

Note In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question. For additional information about how to obtain the latest ISA Server service pack, click the following article number to view the article in the Microsoft Knowledge Base:

313139 How to obtain the latest Internet Security and Acceleration Server 2000 service pack

Prerequisites

To apply this hotfix, you must have ISA Server 2000 Service Pack 1 (SP1) installed on your computer.

File information

The English version of this hotfix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.

   Date        Time    Version      Size     File name
   --------------------------------------------------------
   16-Dec-2003  17:21  3.0.1200.298  393,488  W3proxy.exe
   16-Dec-2003  17:21  3.0.1200.298  299,280  Wspsrv.exe
   16-Dec-2003  17:21  3.0.1200.298  178,448  Mspadmin.exe
   16-Dec-2003  17:21  3.0.1200.298  103,184  Msphlpr.dll

This hotfix also applies to the following language versions of ISA Server 2000:

French
German
Spanish
Japanese

Implement the hotfix

After you apply the hotfix that is described in this article, follow these steps to implement the functionality in this hotfix.

Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

Stop the Web Proxy service.
Start Registry Editor.
Locate and then click the following registry subkey:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W3Proxy\Parameters
Create the following new entry:
Entry name: IgnoreMimeCheckForZeroContentLength
Type: DWORD
Value: 1
Start the Web Proxy service.

To revert to the original configuration, either remove the IgnoreMimeCheckForZeroContentLength registry entry, or change its data value to 0 (zero). After you make either change, restart the Web Proxy service.

After you apply the hotfix that is described in this article and then create the registry entry, ISA Server will not check the content group for any HTTP response with a 100 HTTP status code, a 204 HTTP status code, or a 304 HTTP status code unless a Content-type header is also specified in the response. ISA Server will allow these responses because the responses must not include a message-body and therefore do not require a Content-type header. ISA Server will also allow any other HTTP response without a Content-type header if that response also has a Content-length header of 0. However, if the response contains a Content-type header, ISA Server will apply restrictions that are based on the content groups that are allowed in the site and content rule. Additionally, if the response has no Content-type header, and if the Content-length header is not 0, ISA Server will apply content group restrictions for all HTTP responses, including the 100 HTTP status code, the 204 HTTP status code, and the 304 HTTP status code.

If a Web server incorrectly sends a message-body in an HTTP response with a Content-length header of 0, ISA removes the message-body from the response before ISA sends only the HTTP response headers back to the Web Proxy client. This behavior also occurs with HTTP responses that include a Content-type header if that content type (or the requested file name extension if there is no Content-type header in the response) is specified in the content group that is allowed. This behavior only occurs after the hotfix is applied and after the IgnoreMimeCheckForZeroContentLength registry entry is created.