Overview

Code access security is a resource constraint model that allows administrators to determine if and how particular code is able to access specified resources and perform other privileged operations. For example, an administrator might decide that code downloaded from the Internet should not be given permission to access any resources, while Web application code developed by a particular company should be offered a higher degree of trust and, for example, be allowed to access the file system, the event log, and Microsoft SQL Server databases.

Traditional principal-based security, such as that provided by the operating system, authorizes access to resources based on user identity. For example, programs launched by a local administrator have no limitations on the local machine. Unfortunately, if the administrator's identity is spoofed and a malicious user is able to execute code using the administrator's security context, the malicious user also has no restrictions. This is where code access security is important because it can provide additional restrictions and security based on the code itself, rather than the user running the code.

With Microsoft .NET Framework version 1.1, administrators can configure policy for ASP.NET Web applications and Web services, which might consist of multiple assemblies. They can also grant code access security permissions to allow the application to access specific resource types and to perform specific privileged operations.

Note  

Web applications and Web services built using .NET Framework version 1.0 always run with unrestricted code access permissions. This is not configurable.

Using code access security with Web applications helps you provide application isolation in hosted environments where multiple Web applications run on the same Web server. Internet service providers (ISPs) that run multiple applications from different companies can use code access security to:

• Isolate applications from each other .

  For example, code access security can be used to ensure that one Web application cannot write to another Web application's directories.

• Isolate applications from system resources .

  For example, code access security can restrict access to the file system, registry, event logs, and network resources, as well as other system resources.

Code access security is one mechanism that can be used to help provide application isolation. Microsoft Windows Server 2003 and Internet Information Services (IIS) 6.0 also provide process isolation for Web applications. Process isolation combined with code access security provides the recommended model for application isolation. For more information, see Chapter 20, "Hosting Multiple ASP.NET Applications."