The Kubernetes kube-apiserver in versions v1.6-v1.15, and versions prior to v1.16.13, v1.17.9 and v1.18.6 are vulnerable to an unvalidated redirect on proxied upgrade requests that could allow an attacker to escalate privileges from a node compromise to a full cluster compromise.
https://security.netapp.com/advisory/ntap-20200810-0004/
https://groups.google.com/d/msg/kubernetes-security-announce/JAIGG5yNROs/19nHQ5wkBwAJ