The compression and caching functionalities of ISA Server 2004 and ISA Server 2006 may cause file corruption in files that are larger than 64 KB

Consider the following scenario:

• You configure Microsoft Internet Security and Acceleration (ISA) Server 2004 or ISA Server 2006 to enable HTTP compression.
  
  Note After you enable HTTP compression, ISA Server requests compression from the Web server for the requested resource.
• A client requests to download a file through ISA Server.
• ISA Server returns a non-compressed response to the client. For example, ISA Server is not configured to return a compressed response to the client. Or, the client makes an HTTP 1.0 request to ISA Server.
• The file is larger than 64 kilobytes (KB).
• You enable the caching functionality in ISA Server.
• The response from the Web server is cacheable.
• The response of the requested file is already cached by ISA Server.

In this scenario, the client receives a corrupted file.

In the scenario that is mentioned in the "Symptoms" section, when ISA Server receives a compressed response, it caches the response as both a compressed version and a non-compressed version. Because of an issue in ISA Server, if the response is larger than 64 KB, the non-compressed version is corrupted while it is being cached. Therefore, the subsequent non-compressed responses that are sent to the client are corrupted.

ISA Server 2006

To resolve this issue, apply ISA Server 2006 Service Pack 1 (SP1).

For more information about how to obtain ISA Server 2006 Service Pack 1, click the following article number to view the article in the Microsoft Knowledge Base:

ISA Server 2004

Hotfix information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, submit a request to Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

Prerequisites

You must have ISA server 2004 Service Pack 3 installed to apply this hotfix.

Restart requirement

You do not have to restart the computer after you apply this hotfix. However, services that are related to ISA Server 2004 will be automatically stopped and then restarted after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

File information

The English version of this hotfix has the file attributes (or later file attributes) 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 item in Control Panel.

ISA Server 2004 Enterprise Edition
ISA Server 2004 Standard Edition

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

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base: