CNTR-K8-002010 - Kubernetes must have a pod security policy set.

Information

Enabling the admissions webhook allows for Kubernetes to apply policies against objects that are to be created, read, updated, or deleted. By applying a pod security policy, control can be given to not allow images to be instantiated that run as the root user. If pods run as the root user, the pod then has root privileges to the host system and all the resources it has. An attacker can use this to attack the Kubernetes cluster. By implementing a policy that does not allow root or privileged pods, the pod users are limited in what the pod can do and access.

NOTE: Nessus has not performed this check. Please review the benchmark to ensure target compliance.

Solution

From the Master node, save the following policy to a file called restricted.yml.

apiVersion: policy/v1beta1
kind: PodSecurityPolicy
metadata:
name: restricted
annotations:
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

See Also

https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_Kubernetes_V1R6_STIG.zip

Item Details

Category: ACCESS CONTROL

References: 800-53|AC-6(8), CAT|I, CCI|CCI-002233, Rule-ID|SV-242437r821610_rule, STIG-ID|CNTR-K8-002010, Vuln-ID|V-242437

Plugin: Unix

Control ID: 12e8fd9ac6bd455c1d6fb66f11c75f7c39e237e8eda321b2fe9581d2eb544f81