* 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:

- Fixed an issue where the API server did not send impersonated UID to authentication webhooks. ([#116681](https://github.com/kubernetes/kubernetes/pull/116681), [@stlaz](https://github.com/stlaz)) [SIG API Machinery and Auth]

### 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: Authorization webhooks now report the following metrics:
  - apiserver_authorization_webhook_evaluations_total
  - apiserver_authorization_webhook_duration_seconds

- APIServerTracing now collects spans from outgoing requests to admission webhooks. ([#103601](https://github.com/kubernetes/kubernetes/pull/103601), [@dashpole](https://github.com/dashpole)) [SIG API Machinery]
- Add a namespace label for all `apiserver_admission_* metrics`.

* [alpha] Adding admissionregistration API group which enables dynamic registration of initializers and external admission webhooks. ([#46294](https://github.com/kubernetes/kubernetes/pull/46294), [@caesarxuchao](https://github.com/caesarxuchao))


### **Application Deployment**
#### StatefulSet

- Added the ability to host webhooks in the cloud controller manager. ([#108838](https://github.com/kubernetes/kubernetes/pull/108838), [@nckturner](https://github.com/nckturner))

    * Before, when users run admission webhook as an addon pod, after they remove the webhook, kube-addon-manager won't cleanup the webhook configuration `MutatingWebhookConfiguration`/`ValidationWebhookConfiguration`, because those resources are not prune-whitelisted. Cluster will go into a bad state that no pod can be admitted.

- Kube-apiserver: timeouts configured for authorization webhooks in the --authorization-config file are now honored, and webhook timeouts are accurately reflected in webhook metrics with result=timeout ([#125552](https://github.com/kubernetes/kubernetes/pull/125552), [@liggitt](https://github.com/liggitt)) [SIG API Machinery, Auth and Testing]

- Added a new metric `webhook_fail_open_count` to monitor webhooks that fail to open. ([#107171](https://github.com/kubernetes/kubernetes/pull/107171), [@ltagliamonte-dd](https://github.com/ltagliamonte-dd))