Article ID: 923318
Article Last Modified on 12/4/2007
APPLIES TO
- Microsoft Internet Security and Acceleration Server 2004 Enterprise Edition
- Microsoft Internet Security and Acceleration Server 2004 Standard Edition
SYMPTOMS
After you configure a Web chaining rule in 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.
CAUSE
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.
RESOLUTION
To resolve this problem, install the hotfix package that is mentioned in the following Microsoft Knowledge Base article:
923767 Description of the ISA Server 2004 hotfix package: August 15, 2006
WORKAROUND
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.
STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Keywords: kberrmsg kbtshoot kbbug kbfix kbfirewall kbprb KB923318
