9.5 Code Access Security

Code access security is a new .NET runtime feature that can dramatically reduce the likelihood of applications performing damaging actions by putting significant restrictions in place on untrusted or partially trusted code. While using code access security programmatically in an application is well beyond the scope of this book, even if you never call a single method related to code access security, your ASP.NET applications still use it through settings configured in the machine.config configuration file.

The <trustLevel> element in machine.config defines the mapping of named trust levels to policy files that define the code access security policies associated with a given named trust level. The <trust> element in machine.config sets the default trust level to Full.

If you want to restrict the actions that a given application can take, you can do so by adding a <location> tag to machine.config that specifies the path to that application and contains a <trust> element specifying the desired trust level, as shown in the following code snippet. Setting the allowOverride attribute to False will prevent the trust level from being overridden in the application's web.config file:

<location path="Application1" allowOverride="False">
   <system.web>
      <trust level="Low"/>
   </system.web>
</location>

As with web.config, the <location> tag in machine.config must be placed outside of the <system.web> tags, but must also appear after the <configSections> section, or an exception will be thrown.