Title

Rancher RKE2 must prevent nonprivileged users from executing privileged functions to include disabling, circumventing, or altering implemented security safeguards/countermeasures. (Cat II impact)

Discussion

Admission controllers intercept requests to the Kubernetes API before an object is instantiated. Enabling the admissions webhook allows for Kubernetes to apply policies against objects that are to be created, read, updated or deleted. Admissions controllers can be used for: - Prevent pod’s ability to run privileged containers - Prevent pod’s ability to use privileged escalation - Controlling pod’s access to volume types - Controlling pod’s access to host file system - Controlling pod’s usage of host networking objects and configuration Satisfies: SRG-APP-000340-CTR-000770, SRG-APP-000342-CTR-000775

Check Content

If using RKE2 v1.24 or older: On the Server Node, run the command: kubectl get podsecuritypolicy For any pod security policies listed, with the exception of system-unrestricted-psp (which is required for core Kubernetes functionality), edit the policy with the command: kubectl edit podsecuritypolicy policyname Where policyname is the name of the policy Review the runAsUser, supplementalGroups, and fsGroup sections of the policy. If any of these sections are missing, this is a finding. If the rule within the runAsUser section is not set to "MustRunAsNonRoot", this is a finding. If the ranges within the supplementalGroups section has min set to "0" or min is missing, this is a finding. If the ranges within the fsGroup section have a min set to "0" or the min is missing, this is a finding. If using RKE2 v1.25 or newer: On each controlplane node, validate that the file "/etc/rancher/rke2/rke2-pss.yaml" exists and the default configuration settings match the following: defaults: audit: restricted audit-version: latest enforce: restricted enforce-version: latest warn: restricted warn-version: latest If the configuration file differs from the above, this is a finding.

Fix Text

If using RKE2 v1.24 or older: On each Control Plane node, create the following policy to a file called restricted.yml. apiVersion: policy/v1beta1 kind: PodSecurityPolicy metadata: name: restricted annotations: seccomp.security.alpha.kubernetes.io/allowedProfileNames: 'docker/default,runtime/default' apparmor.security.beta.kubernetes.io/allowedProfileNames: 'runtime/default' seccomp.security.alpha.kubernetes.io/defaultProfileName: 'runtime/default' apparmor.security.beta.kubernetes.io/defaultProfileName: 'runtime/default' spec: privileged: false #Required to prevent escalations to root. allowPrivilegeEscalation: false #This is redundant with non-root + disallow privilege escalation, # but we can provide it for defense in depth. requiredDropCapabilities: - ALL # Allow core volume types. volumes: - 'configMap' - 'emptyDir' - 'projected' - 'secret' - 'downwardAPI' # Assume that persistentVolumes set up by the cluster admin are safe to use. - 'persistentVolumeClaim' hostNetwork: false hostIPC: false hostPID: false runAsUser: # Require the container to run without root privileges. rule: 'MustRunAsNonRoot' seLinux: # This policy assumes the nodes are using AppArmor rather than SELinux. rule: 'RunAsAny' supplementalGroups: rule: 'MustRunAs' ranges: # Forbid adding the root group. - min: 1 max: 65535 fsGroup: rule: 'MustRunAs' ranges: # Forbid adding the root group. - min: 1 max: 65535 readOnlyRootFilesystem: false To implement the policy, run the command: kubectl create -f restricted.yml" If using RKE v1.25 or newer: On each Control Plane node, create the file "/etc/rancher/rke2/rke2-pss.yaml" and add the following content: apiVersion: apiserver.config.k8s.io/v1 kind: AdmissionConfiguration plugins: - name: PodSecurity configuration: apiVersion: pod-security.admission.config.k8s.io/v1beta1 kind: PodSecurityConfiguration defaults: enforce: "restricted" enforce-version: "latest" audit: "restricted" audit-version: "latest" warn: "restricted" warn-version: "latest" exemptions: usernames: [] runtimeClasses: [] namespaces: [kube-system, cis-operator-system, tigera-operator] Ensure the namespace exemptions contain only namespaces requiring access to capabilities outside of the restricted settings above. Once the file is created, restart the Control Plane nodes with: systemctl restart rke2-server

Additional Identifiers

Rule ID: SV-254571r955082_rule

Vulnerability ID: V-254571

Group Title: SRG-APP-000340-CTR-000770

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