Kubernetes must have a pod security policy set.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-242437	CNTR-K8-002010	SV-242437r712667_rule		High

Description
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.

Description

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.

STIG	Date
Kubernetes Security Technical Implementation Guide	2021-04-14

Details

Check Text ( C-45712r712665_chk )
On the Master Node, run the command: kubectl get podsecuritypolicy If there is no pod security policy configured, this is a finding. For any pod security policies listed, edit the policy with the command: kubectl edit podsecuritypolicy policyname (Note: "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 has a min set to "0" or the min is missing, this is a finding.

Check Text ( C-45712r712665_chk )

On the Master Node, run the command:

kubectl get podsecuritypolicy

If there is no pod security policy configured, this is a finding.

For any pod security policies listed, edit the policy with the command:

kubectl edit podsecuritypolicy policyname
(Note: "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 has a min set to "0" or the min is missing, this is a finding.

Fix Text (F-45670r717028_fix)
From the Master node, save 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, 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

Fix Text (F-45670r717028_fix)

From the Master node, save 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,
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