How to sandbox an assembly or C# source file

Question

We want to provide some programmability features to our clients, so we allow them to write their own code, but they must not have access to system features, like

File.Delete( "test.txt" );

We partially accomplished this by not allowing global or local using statements.

But the users still would be able to access all .NET features by writing fully qualified names, like:

System.IO.File.Delete( "test.txt" );

Do you know of ways to restrict certain source files, or complete assemblies, from accessing system functions?

Answer 1

If you are using .net framework (not net core or net5+) you could run the user's code in a separate AppDomain with restricted permissions.

Just a few hints (there are a lot of other permissions you can set):

var setup = new AppDomainSetup();

var perm = new PermissionSet(PermissionState.None);

perm.AddPermission(
       new SecurityPermission(SecurityPermissionFlag.Execution));

perm.AddPermission(
       new FileIOPermission(FileIOPermissionAccess.Read, "PathToReadOnlyFolder"));

var userCodeDomain = AppDomain.CreateDomain("UserCodeDomain", null, setup, perm);