Given a sane language and a sane exposed API, it's not difficult to limit what the remote code can do. It's just that bolting a software-based isolation layer (

Given a sane language and a sane exposed API, it's not difficult to limit what the remote code can do. It's just that bolting a software-based isolation layer ("sandbox") on top of something existing can be expected to yield a few holes in the process. If I were to use anything existing, it would be something like Lua. Just strip away the standard library API and replace it with something strictly under your control.