Medium trust is the default trust level in ASP.NET. It prevents applications from accessing shared system resources and eliminates the potential for application interference.
Trust level refers to permissions set in the Web.config file (see web-config) that dictate what operations can and cannot be performed by Web applications. ASP.NET 3.5 and 4.0 shared hosting servers use the default Medium trust level with the addition of OleDbPermission, OdbcPermission, and a less-restrictive WebPermission.
Applications operating under a Medium trust level have no registry access, no access to the Windows event log, and cannot use ReflectionPermission (but can use Reflection). Such applications can communicate only with a defined range of network addresses and file system access is limited to the application's virtual directory hierarchy.
Using a Medium trust level prevents applications from accessing shared system resources and eliminates the potential for application interference. Adding OleDbPermission and OdbcPermission allows applications to use those data providers to access databases. WebPermission is modified to allow outbound http and https traffic.
