Error message in SecureNAT clients after you configure a Web chaining rule to forward HTTP as HTTPS in ISA Server 2006 or ISA Server 2004: "The target principal name is incorrect"

After you configure a Web chaining rule in Microsoft Internet Security and Acceleration (ISA) Server 2006 or Microsoft Internet Security and Acceleration (ISA) Server 2004, certain clients receive the following error message when they try to connect to the destination Web site:You experience this problem if the following conditions are true:

• You configure the Web chaining rule to forward HTTP traffic as HTTPS traffic.
  
  Note This configuration is known as forward SSL bridging.
• The client computers are configured as SecureNAT clients.

The ISA Server Web Proxy filter verifies that the requested host name matches the common name (CN) that is specified on the SSL certificate from the destination Web server. The Web Proxy filter incorrectly verifies only the host name information that it retrieves from the URL. The Web Proxy filter does not examine the Host header field of the particular request.

This problem occurs because a SecureNAT client makes a request to an IP address. When the Web Proxy filter creates the proxy format URL, the Web Proxy filter uses the destination IP address information and not the Host header information in this request. In this situation, the certificate verification operation fails because the Web Proxy filter compares the IP address to the common name of the SSL certificate.

To resolve this problem, obtain the latest ISA Server Service Pack that is mentioned in the following Microsoft Knowledge Base articles:

To work around this problem, configure the client computer as a Web proxy client of the ISA Server computer. Then, the Web Proxy filter receives the correct URL in the request. Therefore, if the fully qualified domain name that is specified in the request matches the common name of the certificate, the certificate verification operation is successful.

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

For more information about how to install ISA Server hotfixes and updates, click the following article number to view the article in the Microsoft Knowledge base: