GHSA-hwm2-4ph6-w6m5: Rancher's restricted PodSecurityPolicy does not prevent containers from running as a privileged user
ImpactThe `restricted` pod security policy (PSP), provided in Rancher versions from 2.0 up to and including 2.6.3, has a deviation from the [upstream](https://github.com/kubernetes/website/blob/6d22e08903d7dd44b049c4689fa882ae07f67de9/content/en/examples/policy/restricted-psp.yaml) `restricted` policy provided in Kubernetes, in which Rancher's PSP has `runAsUser` set to `runAsAny`, while upstream has `runAsUser` set to `MustRunAsNonRoot`. This allows containers to run as any user, including a privileged user (`root`), even when Rancher's `restricted` policy is enforced on a project or at cluster level.A new `restricted-noroot` PSP was created to  prevent pods from running as `root` when this policy is enforced. This new policy was introduced, instead of patching the current provided `restricted` policy, in order to avoid breaking users' workloads that are using the `restricted` PSP and that might be running as a privileged user.**Note**: Running containers as `root` increases the risk of a compromised container being used by a malicious actor as an attack platform to further exploit the user's environment. It is a security best practice to avoid running containers as a privileged user and to limit its usage to workloads where it is strictly necessary.PatchesPatched versions include release 2.6.4 and later versions. The existing `restricted` PSP in Rancher 2.6.4 was not modified and still allows containers to run as a privileged user, as explained above. This fix was not backported to previous releases.For Rancher 2.6.4 and later releases, users using the current `restricted` PSP and that want to prevent containers from running as `root`, are advised to migrate to the new `restricted-noroot` policy. Before doing this migration, it is necessary to verify if affected workloads are currently running as a privileged user and modify them accordingly to the users' own environment to run as a non-privileged user. A redeployment of the affected workload is necessary in order for the new PSP to take effect.WorkaroundsFor users running Rancher 2.6.3 and previous releases, which did not received this backport and that want to benefit from this fix, they can manually create a new `restricted-noroot` PSP on their clusters through Rancher UI. The template of the `restricted-noroot` policy provided in Rancher 2.6.4 is available in the [source code](https://github.com/rancher/rancher/blob/7410cef256c9ed22e8bf4609e5b2e9a1f63a0d05/pkg/data/management/podsecuritypolicytemplate_data.go#L101-L145). As a reminder, it is also necessary to manually verify and redeploy the running workload before enabling a more restricted pod security policy.ReferencesFor instructions on how to configure pod security policies using Rancher, please refer to the [documentation](https://rancher.com/docs/rancher/v2.6/en/admin-settings/pod-security-policies/) page. For more information on PSPs in Kubernetes, please refer to the Kubernetes [documentation](https://kubernetes.io/docs/concepts/policy/pod-security-policy/) ([permalink](https://github.com/kubernetes/website/blob/f5ec6b03db0925dc2b9cb9bbdc8135dcbeacbe0e/content/en/docs/concepts/policy/pod-security-policy.md)).**Important reminder:** Pod security policies are considered deprecated since Kubernetes v1.21, and will be removed in Kubernetes v1.25. Consult Kubernetes' [documentation](https://kubernetes.io/docs/tasks/configure-pod-container/migrate-from-psp/) ([permalink](https://github.com/kubernetes/website/blob/f5ec6b03db0925dc2b9cb9bbdc8135dcbeacbe0e/content/en/docs/tasks/configure-pod-container/migrate-from-psp.md)) regarding how to migrate from PodSecurityPolicy to Kubernetes' built-in PodSecurity Admission Controller. For the list of supported Kubernetes versions in Rancher, please consult our [support matrix](https://www.suse.com/suse-rancher/support-matrix/all-supported-versions/).For more informationIf you have any questions or comments about this advisory:Reach out to [SUSE Rancher Security team](https://github.com/rancher/rancher/security/policy) for security related inquiries.Open an issue in [Rancher](https://github.com/rancher/rancher/issues/new/choose) repository.Verify our [support matrix](https://www.suse.com/suse-rancher/support-matrix/all-supported-versions/) and [product support lifecycle](https://www.suse.com/lifecycle/).
CVSS v4.0: 7.1