Improving Web Application Security: Threats and - CGISecurity

222 Part III: Building Secure Web ApplicationsTraditional principal-based security, such as that provided by the operating system,authorizes access to resources based on user identity. For example, programslaunched by a local administrator have no limitations on the local machine.Unfortunately, if the administrator’s identity is spoofed and a malicious user is ableto execute code using the administrator’s security context, the malicious user also hasno restrictions. This is where code access security is important because it can provideadditional restrictions and security based on the code itself, rather than the userrunning the code.With Microsoft .NET Framework version 1.1, administrators can configure policy forASP.NET Web applications and Web services, which might consist of multipleassemblies. They can also grant code access security permissions to allow theapplication to access specific resource types and to perform specific privilegedoperations.Note Web applications and Web services built using .NET Framework version 1.0 always run withunrestricted code access permissions. This is not configurable.Using code access security with Web applications helps you provide applicationisolation in hosted environments where multiple Web applications run on the sameWeb server. Internet service providers (ISPs) that run multiple applications fromdifferent 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 applicationcannot 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 applicationisolation. Microsoft Windows Server 2003 and Internet Information Services (IIS)6.0 also provide process isolation for Web applications. Process isolation combinedwith code access security provides the recommended model for application isolation.For more information, see Chapter 20, “Hosting Multiple ASP.NET Applications.”