Is it even possible to make a 100% standards conforming parser that is not vulnerable to at least DoS attacks? (Automatically fetching XSDs e.g. sounds nice in

Is it even possible to make a 100% standards conforming parser that is not vulnerable to at least DoS attacks? (Automatically fetching XSDs e.g. sounds nice in practice, until you realize that it means your server will make HTTP requests to user-supplied URLs, so most parsers come with an option to disable it, which may or may not break documents relying on it.)