Improving Web Application Security: Threats and - CGISecurity

226 Part III: Building Secure Web ApplicationsTable 9.1 Restrictions Imposed by the ASP.NET Trust LevelsASP.NETTrust Level Main RestrictionsFullUnrestricted permissions. Applications can access any resource that is subject tooperating system security. All privileged operations are supported.HighNot able to call unmanaged codeNot able to call serviced componentsNot able to write to the event logNot able to access Microsoft Message Queuing queuesNot able to access OLE DB data sourcesMediumLowMinimalIn addition to the above, file access is restricted to the current application directoryand registry access is not permitted.In addition to the above, the application is not able to connect to SQL Server andcode cannot call CodeAccessPermission.Assert (no assertion security permission).Only the execute permission is available.Locking the Trust LevelIf a Web server administrator wants to use code access security to ensure applicationisolation and restrict access to system level resources, the administrator must be ableto define security policy at the machine level and prevent individual applicationsfrom overriding it.Application service providers or anyone responsible for running multiple Webapplications on the same server should lock the trust level for all Web applications.To do this, enclose the element in Machine.config within a tag,and set the allowOverride attribute to false, as shown in the following example.You can also use a path attribute on the element to apply a configurationto a specific site or Web application that cannot be overridden. For more informationabout the element, see Chapter 19, “Securing Your ASP.NET Applicationand Web Services.”