- `Kubelet` no longer creates certain legacy iptables rules by default.
  It is possible that this will cause problems with some third-party components
  that improperly depended on those rules. If this affects you, you can run

- The kube-proxy `sync_proxy_rules_iptables_total` metric has now reverted back
  to its pre-1.27 behavior of tracking the total number of iptables rules that
  kube-proxy is responsible for, rather than only counting the number of rules
  that it re-synced on the last sync. The new `sync_proxy_rules_iptables_last`

* Fix issue where masquerade rules are flushed in GCE k8s clusters. ([#56729](https://github.com/kubernetes/kubernetes/pull/56729), [@dnardo](https://github.com/dnardo))
* kubelet: Fix bug where `runAsUser: MustRunAsNonRoot` strategy didn't reject a pod with a non-numeric `USER`. ([#56708](https://github.com/kubernetes/kubernetes/pull/56708), [@php-coder](https://github.com/php-coder))

- In "large" clusters, kube-proxy in iptables mode will now sometimes
  leave unused rules in iptables for a while (up to `--iptables-sync-period`)
  before deleting them. This improves performance by not requiring it to
  check for stale rules on every sync. (In smaller clusters, it will still
  remove unused rules immediately once they are no longer used.)

- kubeadm: Added better handling of errors during unmount when calling `kubeadm reset`. When failing to unmount directories under `/var/run/kubelet`, kubeadm will now throw an error instead of showing a warning and continuing to clean up said directory. In such situations, it is better for you to inspect the problem and resolve it manually. Then, you can call `kubeadm reset` again to complete the cleanup.

## Changelog since v1.26.8

## Changes by Kind

### API Change

- Fixed a bug where CEL expressions in CRD validation rules would incorrectly compute a high estimated cost for functions that return strings, lists or maps.

- Fixes a race condition in the iptables mode of kube-proxy in 1.27 and later
  that could result in some updates getting lost (e.g., when a service gets a
  new endpoint, the rules for the new endpoint might not be added until
  much later). ([#122756](https://github.com/kubernetes/kubernetes/pull/122756), [@hakman](https://github.com/hakman)) [SIG Network]