How IIS Launches a CGI Application

The information in this article applies to:

• Microsoft Internet Information Server versions 1.0 and 2.0

SYMPTOMS

When you access an HTML page, and the anonymous account does not have access to the file, the Internet Information Server (IIS) internally reports an error message then sends the authentication method selected by the Web Administrator (Basic or Windows NT Challenge).

However, CGI/ISAPI works differently. If Allow Anonymous user authentication is enabled, and you go to a URL that is protected by a Windows NT (NTFS) partition, the server will first try to run the application using the Anonymous account. If the account is allowed to run the application via NTFS, then the application will run, and the server will send the output to you.

CAUSE

The problem occurs when the Anonymous account does not have rights to the CGI. When you try to launch the CGI application, IIS uses the Anonymous user. Because the account does not have rights to the file, the process fails to run and an error message is returned via STDOUT.

However, to IIS the process appears to launch and terminate normally. Because the Access Denied error message is placed in STDOUT, IIS has no way of knowing that the process failed. Therefore, it does not try any other authentication methods because the Anonymous account was able to launch the process. IIS uses the createprocessasuser API call to launch the CGI application. Createprocessasuser will terminate normally if the user does not have NTFS rights to that CGI/ISAPI application.

WORKAROUND

Use one of the following methods:

WARNING: Using Registry Editor incorrectly can cause serious, system-wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at your own risk.

• Modify the registry to run all applications as the system.

  Under the W3SVC/Parameters, place the value CreateProcessAsUser as a REG_DWORD and give it a value of 0. This causes the CGI to be ran with the CreateProcess API and run in the system context. This has serious security implications because CGI scripts will have much greater access to the system than they normally would.

  NOTE: All users would be able to launch CGI no matter what user they are authenticated as.

• You can also run the CGI/ISAPI from a secured web page. If you run it from a secured web page, you will have to either be authenticated by Basic or NT Challenge. When you click the URL for the CGI/ISAPI, it will pass the REMOTE_USER environment variable, and the CreateProcessAsUser API will use that user to run the CGI. Anonymous will not be used in that instance because a user account has already being passed to the server.
• Turn off Anonymous access to the server, and use only Basic or NT Challenge.