How Secure Is WebAssembly?

The story with WebAssembly is that the binary can only do what you give it access to. So, if you think about like a normal Ruby program that you run on your Web server, you've got a Rails server, you install a gem. If that gem decides it wants to access the internet, it probably can. You can't really do much about it. It just goes and does it. With WebAssembly, you tell each binary that you run what it's allowed to access by providing it functions that it calls.