Invalid Content-Length Header May Cause Requests to Fail Through ISA Server

When you send a HTTP POST request from a Web browser through Internet Security and Acceleration (ISA) Server 2000, you may receive the following error message in the Web browser: This error message may be the only response that is displayed in the Web Browser, or it may be displayed together with the correct response in the same HTML page.

This error message may be displayed in both a Web publishing scenario or for Web proxy clients behind ISA Server that are accessing Web servers on the Internet.

This problem occurs because certain Web browsers send two extra bytes (Carriage Return and Line Feed) at the end of the message body (data portion) of an HTTP POST request. However, the Web browser does not reflect these two extra bytes in the HTTP content-length header, which causes the message body to contain two more bytes than the HTTP content-length header indicates.

The Web Proxy service in ISA Server 2000 contains checks for this condition, which cause the "400 Bad Request" error message to be returned when the Web browser send an invalid content-length header.

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. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

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, contact 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. The English version of this fix should have the following file attributes or later:

To work around this problem in a publishing scenario, use server publishing instead of Web publishing. Because server publishing does not work at the application layer, server publishing cannot detect the mismatch between the content-length header and the actual length of the data that is sent.

For outgoing Web requests, use a SecureNAT or firewall client; this should work as long as the HTTP redirector application filter is disabled or is configured to access the Web server directly.

A Web browser that does not send invalid content-length headers works correctly, and is therefore the optimal solution.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.

The HTTP 1.1 Request for Comments (RFC) document clearly states that sending an invalid content-length header is not acceptable for an HTTP 1.1 client or server. Although the fix that is described in this article is designed to be installed on ISA Server 2000, strictly speaking, it is the Web browser that should be corrected so that it does not send an invalid content-length header.