Yes, assuming there's no flaws in the interpreter. But they're all moving full steam ahead in the browsers right now, so imagine it's deemed as safe as javascript. The current push is to divvy up the permissions of certain resources such as sockets and filesystem (browser code don't have filesystem access) and make an API to ensure that modules don't overstep their granted permissions. It'll probably look a lot like node and npm, where you could add a module to your source and know that it can't access things it shouldn't. Pretty exciting stuff. It's a true merger of all languages together under one runtime.

That's true, but that's a class of exploits that is mostly impossible anyway (except in an embedded environment). Most systems that have an MMU ensure that no page is both writeable and executable, meaning you can't inject code. This forces attackers to use ROP.