CVE-2021-25735

Access Restriction Bypass in kube-apiserver in k8s.io/kubernetes

A vulnerability in Kubernetes `kube-apiserver` could allow node updates to bypass a _Validating Admission Webhook_ and allow unauthorized node updates. The information that is provided to the admission controller could contain old configurations that overwrite values used for validation. Since the overwriting takes place before the validation, this could lead the admission controller to accept requests that should be blocked. The vulnerability can be exploited when an update action on node resources is performed and an admission controller is in place and configured to validate the action. Users are only affected by this vulnerability if they are running a _Validating Admission Webhook_ for Nodes that denies admission based partially on the old state of the Node object. It only impacts validating admission plugins that rely on old values in certain fields and does not impact calls from kubelets that go through the built-in NodeRestriction admission plugin.

Se ha detectado un problema de seguridad en kube-apiserver que podría permitir a las actualizaciones de los nodos omitir un Validating Admission Webhook. Los clusters sólo están afectados por esta vulnerabilidad si ejecutan un Validating Admission Webhook para nodos que deniega la admisión basándose, al menos parcialmente, en el estado antiguo del objeto Node. El Validating Admission Webhook no comprueba algunos campos anteriores.