Where can I read about the bug? And what is the bug? If there is no authenticationData it is authenticated by default or what?
Link to the patch fixing it: https://github.com/kubernetes/kubernetes/commit/7fef0a4f6a44...
Of course, we'd already fixed other issues like Kubelet listening on a secondary debug port with no authentication. Those problems stemmed from its origins as a make-it-possible hacker project and it took a while to pivot it to something usable in an enterprise.
If there is no authenticationData then the if !Ok is never run and the code continues execution as it were authenticated.