Depending on the deployment method, you have numerous ways to specify which security level to grant a CLR assembly. All of them demand that you specify one of three permission sets:
Safe. Assembly can perform local data access and computational tasks only.
External_Access. Assembly can perform local data access and computational tasks and also access the network, the file system, the registry, and environment variables. Although External_Access is less restrictive than Safe, it still safeguards server stability.
Unsafe. Assembly has unrestricted permissions and can even call unmanaged code. This setting can significantly compromise SQL Server security; only members of the sysadmin role can create (load) unsafe assemblies. Also note that ...