IIS: Authentication & Security Features

The information in this article applies to:

• Microsoft Internet Information Server version 1.0

SUMMARY

This article describes the Authentication & Security Features of Microsoft Internet Information Server.

MORE INFORMATION

Integration with Windows NT

The World Wide Web (WWW), Gopher, and FTP services included with the Microsoft Internet Information Server are fully integrated with Windows NT Server user accounts and file access permissions.

Every access to a resource (for example, a file, an HTML page, an Internet Server API (ISAPI) application, etc.) is done by the services on behalf of a Windows NT user. The service impersonates the user by supplying a username/password pair in the attempt to read/execute the resource for the client.

The Windows NT File System (NTFS) allows Access Control Lists (ACLs) to be assigned to files and directories. ACLs grant and/or deny access to the associated file or directory by specific Windows NT user accounts, or groups of users. When an Internet service attempts to read or execute a file on behalf of a client request, the user account offered by the service must have permission, as determined by the ACL associated with the file, to read or execute the file, as appropriate. If the user account does not have permission to access the file, the request fails, and a response is returned, informing the client that access has been denied.

File and directory ACLs are configured using the Windows NT File Manager.

Anonymous Connections

An anonymous connection is processed when a client request does not contain a username and password. This occurs in the following cases:

• An FTP client logs on with the username Anonymous.
• All Gopher requests.

Each Internet service maintains a Windows NT username and password to be used for the processing of anonymous requests. When an anonymous request is received, the service impersonates the user configured as the anonymous-logon user. The request will succeed if the anonymous-logon user has permission to access the requested resource, as determined by the resource's ACL. For WWW only, if the user does not have permission to access the resource, the response returned to the client contains a list of supported authentication schemes for gaining access to the resource. See below for more information.

The anonymous-logon user account can be viewed and modified on the Service property page of the Internet Service Manager. Multiple Internet Information Server services running on the same computer can use the same, or different anonymous-logon user accounts. Including the 'anonymous logon' user account in file or directory ACLs allows for precise control of the resources available to 'anonymous' clients.

The anonymous-logon user account specified must be a valid Windows NT user account on the server computer, and the password specified must match the password for this user in the computer's user database. User accounts and passwords are configured using the Windows NT User Manager.

When the Internet Information Server product is installed, Setup creates a user account on the server computer to be used for anonymous connections. The username of this account has the form IUSR_<computer_name>. For example, if the server computer name is WEB1, the username created will be IUSR_WEB1. The same anonymous-logon user account is set up for all Internet Information Server services installed on the computer. The account is made a member of the computer's Guest group. This will, in most cases, give anonymous client requests access to public content published on the server. Run the Control Panel/Network applet to see the computer name configured for the Windows NT Server computer.

A randomly generated password is created for the IUSR_<computer_name> account. For maximum convenience and security, we suggest that you change the password associated with this account to a password that you will remember, but is not easily guessed. To do this, you must specify the new password for the account in User Manager, and on the Service page of the Internet Service Manager for each Internet Information Server service installed.

When the Internet Information Server is installed on a primary or secondary domain controller, the anonymous-logon user account is created in the user account database of the domain. When Internet Information Server is installed on a domain member-server, or a stand-alone server, the account is created on the local machine.

If Internet Information Server is installed on multiple domain controllers of the same domain, a separate user account is created in the domain user database for each Internet server computer. This does not cause any conflicts since each username is unique, containing the name of the associated computer.

However, you may find it more convenient to create a single anonymous-logon user account in the domain to use for all Internet Information Server domain controllers in the domain. This can simplify administration of ACLs. To do this, follow these steps:

1. In User Manager, create a new anonymous-logon user account in the domain. Be sure that this account is made a member of appropriate groups, given a secure password, and is given the User Right (in the Policies menu) to Log On Locally.

2. On the Service property page of Internet Service Manager, specify the new anonymous-logon username and password. You must do this for each Internet Information Server service running on all primary and secondary domain controllers in the domain.

3. When later installing Internet Information Server on other domain controllers in the domain, be sure to use Internet Service Manager to modify the anonymous-logon username and password to match those created with User Manager. Do this for each Internet Information Server service installed.

Client Requests Containing Credentials

A request containing credentials is one of the following:

• An FTP client logs on with a valid Windows NT username and password.

  This requires that the FTP service checkbox labled Allow Only Anonymous Connections be unchecked. WARNING: FTP sends passwords across the network in clear text.

• A WWW (HTTP) request's headers contain a username and password.

  This is HTTP basic authentication. WARNING: HTTP basic authentication sends passwords across the network in clear text.

• A WWW browser supports NTLM (Windows NT native) authentication, and an anonymous client request is denied access to a resource.

  In this case, the browser automatically sends the Windows client's username and password to the Internet Information Server Web server using the encrypted NTLM protocol. In this release, only the Internet Explorer 2.0 & 3.0 for Windows 95 supports NTLM authentication.

For WWW (HTTP) only, when an anonymous request fails because the anonymous-logon user account does not have permission to access the desired resource, the response to the client indicates which authentication schemes the service supports. This is determined by the configuration of the WWW service authentication features. If the response indicates to the client that the service is configured to support HTTP basic authentication, most Web browsers will pop up a username/password dialog box, and reissue the anonymous request as a request with credentials, including the username and password entered by the user.

If a Web browser supports NTLM authentication, and the Web service is configured to support NTLM authentication, an anonymous WWW request failing due to permissions, will result in automatic use of the NTLM protocol to send a username and encrypted password from the client to the service. The client request will then be reprocessed, using the client's user information. The user account obtained from the client is that with which the user is logged into the client computer. As this account, including its Windows NT domain, must be a valid account on the Web server machine, NTLM authentication is most useful in an intranet environment, where the client and server machines are in the same, or trusted domains. In this release, Internet Explorer for Windows 95 is the only browser that supports NTLM authentication.

Internet Service Manager Authentication Options

In addition to the anonymous-logon username and password fields, the Internet Service Manager Service property page contains the following authentication options:

For WWW:

• Allow Anonymous.

  When this check box is checked, anonymous connections are processed, and the anonymous-logon username/password are used for these connections. When this checkbox is unchecked, all anonymous connections are rejected. In this case, basic or NTLM authentication can be used to access content.

• Basic.

  When this check box is checked, the Web service will process requests using basic authentication. WARNING: Basic authentication sends Windows NT usernames and passwords across the network without encryption. This checkbox is unchecked by default for security reasons.

• Windows NT Challenge/Response.

  When this check box is checked, the service will honor requests by clients to send user account information using the Windows NT Challenge/Response (NTLM) protocol. This protocol uses encryption for secure transmission of passwords. The NTLM authentication process is initiated automatically as a result of an 'access denied' error on an anonymous client request. Currently, NTLM authentication only works with Internet Explorer 2.0 for Windows 95.

• Allow Anonymous Connections.

  When this check box is checked, FTP logons in which the user enters a username of 'anonymous' will be processed. These anonymous connections will be processed on behalf of the Windows NT user account specified on the Service property page. When this check box is unchecked, users will be required to enter valid Windows NT usernames and passwords to log on to the FTP service.

• Allow only anonymous connections.

  When this checkbox is checked, user logons with a username other than anonymous will be rejected.

  WARNING: FTP User names and passwords are sent across the network in clear text. When this check box is unchecked, Windows NT passwords will be sent to the server without encryption. This check box is checked by default for security reasons.

Other Authentication Issues

SSL:

SSL is a WWW feature that supports data encryption and server authentication. All data sent to or from the client using SSL is encrypted. If HTTP basic authentication is used in conjunction with SSL, the username and password are transmitted after being encrypted by the client's SSL support. In this release, the only Web browser that supports SSL is Internet Explorer 2.0, for Windows 95. See the Installation and Planning Guide and online help for more information on SSL.

'INTERACTIVE' and 'NETWORK' Users

If you use the predefined Windows NT user accounts 'INTERACTIVE' and

'NETWORK' for access control, your use of these accounts may affect client

Log On Locally User Right

In User Manager, when configuring a Windows NT user account to be used either as the Internet Information Server anonymous-logon account, or as a user account specified by client requests using HTTP basic authentication, be sure that the user account is granted the 'Log on locally' user right. This is specified in User Manager's Policies menu.

Customized Authentication

If you need a WWW request authentication scheme not supported by the service directly, obtain a copy of the Internet Server API (ISAPI) Software Developer's Kit (SDK), and read the ISAPI Filters specification on how to develop user-written ISAPI Filter DLLs that handle request authentication.