An upstream Kubernetes vulnerability (CVE-2019-11247) has been identified where the API server mistakenly allows access to a cluster-scoped custom resource, if the request is made as if the resource were namespaced. Authorisations for the resource accessed in this manner are enforced using roles and role bindings within the namespace. This means that a user with access only to a resource in one namespace could create, view updates or delete the cluster-scoped resource (according to their namespace role privileges).
Charmed Kubernetes has already been patched to mitigate against this vulnerability. Patched builds of the 1.13.8, 1.14.4 and 1.15.1 kube-apiserver snap have also been published.
The vulnerability, of medium severity, has also been patched in the following upstream version of Kubernetes – 1.13.9, 1.14.5 and 1.15.2. Users are encouraged to update to one of these versions now.
To mitigate against the vulnerability in an unpatched version, users should remove authorisation rules that grant access to cluster-scoped resources within namespaces. For example, RBAC roles and clusterroles intended to be referenced by rolebindings should not grant access to `resources:[*], apiGroups:[*]`, or grant access to cluster-scoped custom resources.