*   Webhook admission now takes a config file that describes how to authenticate to webhook servers ([#54414](https://github.com/kubernetes/kubernetes/pull/54414),[ @deads2k](https://github.com/deads2k))

    * can be overridden by explicitly specifying the scope values as
    * comma-separated string in the "users[*].config.scopes" field in the
    * KUBECONFIG file.
* kube-apiserver is changed to use SSH tunnels for webhook iff the webhook is not directly routable from apiserver's network environment. ([#58644](https://github.com/kubernetes/kubernetes/pull/58644), [@yguo0905](https://github.com/yguo0905))

- `apiserver_admission_webhook_admission_duration_seconds` buckets have been expanded, 25s is now the largest bucket size to match the webhook default timeout. ([#115802](https://github.com/kubernetes/kubernetes/pull/115802), [@logicalhan](https://github.com/logicalhan)) [SIG API Machinery and Instrumentation]

- `discovery.k8s.io/v1beta1`...

* The webhook admission plugin now works even if the API server and the nodes are in two separate networks,for example, in GKE.
The webhook admission plugin now lets the webhook author use the DNS name of the service as the CommonName when generating the server cert for the webhook.
Action required:

### CVE-2021-25735: Validating Admission Webhook does not observe some previous fields

A security issue was discovered in kube-apiserver that could allow node
updates to bypass a Validating Admission Webhook. You are only affected
by this vulnerability if you run a Validating Admission Webhook for Nodes
that denies admission based at least partially on the old state of the
Node object.

- Kube-apiserver adds two new alpha metrics `conversion_webhook_request_total` and `conversion_webhook_duration_seconds` that allow users to monitor requests to CRD conversion webhooks, split by result, and failure_type (In case of failure). ([#118292](https://github.com/kubernetes/kubernetes/pull/118292), [@cchapla](https://github.com/cchapla))...

* Fix public IP not found issues for VMSS nodes ([#80703](https://github.com/kubernetes/kubernetes/pull/80703), [@feiskyer](https://github.com/feiskyer))
* Resolves a bug that prevented sending a multi-version custom resource to an admission webhook. ([#79495](https://github.com/kubernetes/kubernetes/pull/79495), [@liggitt](https://github.com/liggitt))

- Introduces a new metric: `admission_webhook_request_total` with the following labels: name (string) - the webhook name, type (string) - the admission type, operation (string) - the requested verb, code (int) - the HTTP status code, rejected (bool) - whether the request was rejected, namespace (string) - the namespace of the...

### CVE-2021-25735: Validating Admission Webhook does not observe some previous fields

A security issue was discovered in kube-apiserver that could allow node
updates to bypass a Validating Admission Webhook. You are only affected
by this vulnerability if you run a Validating Admission Webhook for Nodes
that denies admission based at least partially on the old state of the
Node object.