In issue 1260 I discussed Microsoft’s “apicall” instruction that can invoke a large number of internal emulator apis and is exposed to remote attackers by default in all recent versions of Windows. I asked Microsoft if this was intentionally exposed, and they replied “The apicall instruction is exposed for multiple reasons”, so this is intentional.

https://bugs.chromium.org/p/project-zero/issues/detail?id=1282&desc=2