Article ID: 920913 - View products that this article applies to.
On client computers that are configured to run Microsoft Internet Security and Acceleration (ISA) Server 2004 or ISA Server 2006 as a proxy server, you receive the following error message in response to some HTTP requests:
You experience this problem if the following conditions are true:
400 Bad Request
This problem occurs because ISA Server does not submit a host header to an upstream proxy server if the host header is missing from the client request. Therefore, the upstream proxy server may return the error message that is mentioned in the "Symptoms" section if the client request does not contain a host header.
By default, ISA Server sends HTTP requests as an HTTP 1.1 client. These kinds of client requests must include a host header. This requirement is specified in RFC 2616. Because ISA Server does not add a host header when it proxies the client request, the upstream proxy server may refuse the request.
Note This problem does not occur if the upstream proxy server is running ISA Server. ISA Server does not comply with RFC 2616 requirement to deny a HTTP 1.1 request that does not specify a host header.
To resolve this problem, obtain the latest ISA Server service pack.
For more information about how to obtain the latest ISA Server 2004 service pack, click the following article number to view the article in the Microsoft Knowledge Base:
891024For more information about how to obtain the latest ISA Server 2006 service pack, click the following article number to view the article in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/891024/ )How to obtain the latest ISA Server 2004 service pack
(http://support.microsoft.com/kb/954258/ )How to obtain the latest Internet Security and Acceleration (ISA) Server 2006 Service Pack
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Microsoft provides programming examples for illustration only, without warranty either expressed or implied. This includes, but is not limited to, the implied warranties of merchantability or fitness for a particular purpose. This article assumes that you are familiar with the programming language that is being demonstrated and with the tools that are used to create and to debug procedures. Microsoft support engineers can help explain the functionality of a particular procedure. However, they will not modify these examples to provide extra functionality or construct procedures to meet your specific requirements.
After you install the service pack, you can restore the behavior of the release version of ISA Server. The original behavior is that ISA Server does not add a host header when it proxies an HTTP client request. To restore the original behavior in ISA Server, set the following vendor parameter:
REVERT_920913To set the Revert_920913 vendor parameter, follow these steps:
For more information about how to install ISA Server 2004 hotfixes and updates, click the following article number to view the article in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/885957/ )How to install ISA Server 2004 hotfixes and updates
Article ID: 920913 - Last Review: March 24, 2009 - Revision: 2.0