Internet Information Services

Internet Information Services (IIS) – formerly called Internet Information Server – is a web server application and set of feature extension modules created by Microsoft for use with Microsoft Windows. It is the most used web server after Apache HTTP Server : As of January 2011, it served 21.00% of all websites on the Internet and 16.22% of the one million busiest websites on the Internet. IIS 7.5 supports HTTP, HTTPS, FTP, FTPS, SMTP and NNTP. It is an integral part of Windows Server family of products, as well as all editions of Windows Vista and Windows 7, although some features are not supported on client versions of Windows. IIS is not turned on by default when Windows is installed.

The first Microsoft web server was a research project at European Microsoft Windows NT Academic Centre (EMWAC), part of the University of Edinburgh in Scotland, and was distributed as freeware. However since the EMWAC server was unable to scale sufficiently to handle the volume of traffic going to microsoft.com, Microsoft was forced to develop its own webserver, IIS.

Almost every version of IIS was released either along or with a version of Microsoft Windows operating system. IIS 1.0 was initially released as a free add-on, a set of web-based services for Windows NT 3.51. However, IIS 2.0 was included with Windows NT 4.0. IIS 3.0, which was included with Service Pack 3 of Windows NT 4, introduced the Active Server Pages dynamic scripting environment. IIS 4.0 was released as part of an "Option Pack" for Windows NT 4.0 and dropped support for the Gopher protocol. IIS 5.0 shipped with Windows 2000 and introduced additional authentication methods, management enhancements including a new MMC based administration application, support for the WebDAV protocol, and enhancements to ASP IIS 5.1 shipped with Windows XP Professional, and was nearly identical to IIS 5.0 on Windows 2000 except for several limitations Microsoft introduced. IIS 5.1 supported only 10 simultaneous connections and supported only a single web site. IIS 6.0, included with Windows Server 2003 and Windows XP Professional x64 Edition, added support for IPv6 and included a new worker process model that increased security as well as reliability.

IIS 7.0 was a complete redesign and rewrite of IIS, which shipped with Windows Vista and Windows Server 2008. IIS 7.0 included a new modular design that allowed for a lessened attack surface and increased performance. IIS 7.0 also introduced a hierarchical configuration system allowing for simpler site deploys, a new Windows Forms based management application, new command line management options, and increased support for the .NET Framework. IIS 7.0 on Vista does not limit the number of allowed connections as IIS on XP did, but limits concurrent requests to 10 (Windows Vista Ultimate, Business, and Enterprise Editions) or 3 (Vista Home Premium). Additional requests are queued, which hampers performance, but they are not rejected as with XP.

The current shipping version of IIS is IIS 7.5, included in Windows 7 and Windows Server 2008 R2. IIS 7.5 improved WebDAV and FTP modules as well as command line administration in PowerShell. It also introduced Best Practices Analyzer tool and process isolation for application pools.

a) Versions :

• IIS 1.0, Windows NT 3.51 available as a free add-on
• IIS 2.0, Windows NT 4.0
• IIS 3.0, Windows NT 4.0 Service Pack 3
• IIS 4.0, Windows NT 4.0 Option Pack
• IIS 5.0, Windows 2000
• IIS 5.1, Windows XP Professional and Windows XP Media Center Edition (requires retail CD)
• IIS 6.0, Windows Server 200 and Windows XP Professional x64 Edition
• IIS 7.0, Windows Server 2008 and Windows Vista (Home Premium, Business, Enterprise and Ultimate editions)
• IIS 7.5, Windows Server 2008 R2 and Windows 7

b) Security :

Earlier versions of IIS were hit with a number of vulnerabilities, chief among them CA-2001-19 which led to the infamous Code Red worm; however, both versions 6.0 and 7.0 currently have no reported issues with this specific vulnerability. In IIS 6.0 Microsoft opted to change the behaviour of pre-installed ISAPI handlers, many of which were culprits in the vulnerabilities of 4.0 and 5.0, thus reducing the attack surface of IIS. In addition, IIS 6.0 added a feature called "Web Service Extensions" that prevents IIS from launching any program without explicit permission by an administrator.

In the current release, IIS 7, the components are provided as modules so that only the required components have to be installed, thus further reducing the attack surface. In addition, security features are added such as Request Filtering, which rejects suspicious URLs based on a user-defined rule set.

By default IIS 5.1 and lower run websites in-process under the SYSTEM account, a default Windows account with 'superuser' rights. Under 6.0 all request handling processes have been brought under a Network Services account with significantly fewer privileges so that should there be a vulnerability in a feature or in custom code it won't necessarily compromise the entire system given the sandboxed environment these worker processes run in. IIS 6.0 also contained a new kernel HTTP stack (http.sys) with a stricter HTTP request parser and response cache for both static and dynamic content.

There are various built-in security features from Microsoft. Many companies offer third-party security tools and features, also known as "Web App Firewalls, or Web Application Firewalls." The advantage of such tools is that they offer much more comprehensive elements (such as easy-to-use GUI, etc.) that aid in protecting an IIS installation with an additional layer of protection at a higher level. Though no security system is ever complete, most admins choose to run an application-layer firewall and an Intrusion Prevention System.

c) Features :

IIS 7 is built on a modular architecture. Modules, also called extensions, can be added or removed individually so that only modules required for specific functionality have to be installed. IIS 7 includes native modules as part of the full installation. These modules are individual features that the server uses to process requests and include the following:

• HTTP modules – Used to perform tasks specific to HTTP in the request-processing pipeline, such as responding to information and inquiries sent in client headers, returning HTTP errors, and redirecting requests.
• Security modules – Used to perform tasks related to security in the request-processing pipeline, such as specifying authentication schemes, performing URL authorization, and filtering requests.
• Content modules – Used to perform tasks related to content in the request-processing pipeline, such as processing requests for static files, returning a default page when a client does not specify a resource in a request, and listing the contents of a directory.
• Compression modules – Used to perform tasks related to compression in the request-processing pipeline, such as compressing responses, applying Gzip compression transfer coding to responses, and performing pre-compression of static content.
• Caching modules – Used to perform tasks related to caching in the request-processing pipeline, such as storing processed information in memory on the server and using cached content in subsequent requests for the same resource.
• Logging and Diagnostics modules – Used to perform tasks related to logging and diagnostics in the request-processing pipeline, such as passing information and processing status to HTTP.sys for logging, reporting events, and tracking requests currently executing in worker processes.

IIS 5.0 and higher support the following authentication mechanisms:

• Basic access authentication
• Digest access authentication
• Integrated Windows Authentication
• .NET Passport Authentication (not supported in Windows Server 2008 and above)

IIS 7.5 includes the following additional security features:

• Client Certificate Mapping
• IP Security
• Request Filtering
• URL Authorization

Authentication changed slightly between IIS 6.0 and IIS 7, most notably in that the anonymous user which was named "IUSR_{machinename}" is a built-in account in Vista and future operating systems and named "IUSR". Notably, in IIS 7, each authentication mechanism is isolated into its own module and can be installed or uninstalled.

d) ISS Express :

IIS Express, a lightweight version of IIS, is available as a standalone freeware. It may be installed on Windows XP with Service Pack 3 and subsequent versions of Microsoft Windows. IIS 7.5 Express only supports HTTP and HTTPS protocol. IIS Express can be downloaded separately or as a part of Microsoft WebMatrix.

5) Extensions :

IIS releases new feature modules between major version releases to add new functionality. The following extensions are available for IIS 7.5:

• FTP Publishing Service – Lets Web content creators publish content securely to IIS 7 Web servers with SSL-based authentication and data transfer.
• Administration Pack – Adds administration UI support for management features in IIS 7, including ASP.NET authorization, custom errors, FastCGI configuration, and request filtering.
• Application Request Routing – Provides a proxy-based routing module that forwards HTTP requests to content servers based on HTTP headers, server variables, and load balance algorithms.
• Database Manager – Allows easy management of local and remote databases from within IIS Manager.
• Media Services – Integrates a media delivery platform with IIS to manage and administer delivery of rich media and other Web content.
• URL Rewrite Module – Provides a rule-based rewriting mechanism for changing request URLs before they are processed by the Web server.
• WebDAV – Lets Web authors publish content securely to IIS 7 Web servers, and lets Web administrators and hosters manage WebDAV settings using IIS 7 management and configuration tools.
• Web Deployment Tool – Synchronizes IIS 6.0 and IIS 7 servers, migrates an IIS 6.0 server to IIS 7, and deploys Web applications to an IIS 7 server.