Kubernetes requires an authentication mechanism to enforce users’ privileges. One method of authentication, bearer tokens, are opaque strings used to associate a user with their having successfully authenticated previously. Any user with possession of this token may masquerade as the original user (the “bearer”) without further authentication.

Within Kubernetes, the bearer token is captured within the hyperkube kube-apiserver system logs at high verbosity levels (--v 10). A malicious user with access to the system logs on such a system could masquerade as any user who has previously logged into the system.