Certified Kubernetes Security Specialist CKS Exam Questions

A service account provides an identity for processes that run in a Pod. Answer: See the Explanation below: When you (a human) access the cluster (for example, using kubectl), you are authenticated by the api server as a particular User Account (currently this is usually admin, unless your cluster administrator has customized your cluster). Processes in containers inside pods can also contact the apiserver. When they do, they are authenticated as a particular Service Account (for example, default). When you create a pod, if you do not specify a service account, it is automatically assigned the default service account in the same namespace. If you get the raw js on or yaml for a pod you have created (for example, kubectl get pods/ -o yaml), you can see the spec.service Account Name field has been automatically set. You can access the API from inside a pod using automatically mounted service account credentials, as described in Accessing the Cluster. The API permissions of the service account depend on the authorization plugin and policy in use. In version 1.6+, you can opt out of automounting API credentials for a service account by setting automount Service Account Token: false on the service account: api Version: v1 kind: Service Account metadata: name: build-robot automount Service Account Token: false ... In version 1.6+, you can also opt out of automounting API credentials for a particular pod: apiVersion: v1 kind: Pod metadata: 

name: my-pod

spec:

serviceAccountName: build-robot

automountServiceAccountToken: false

...

The pod spec takes precedence over the service account if both specify

a automountServiceAccountToken value.

Kubernetes auditing provides a security-relevant chronological set of records about a cluster. Kubeapiserver performs auditing. Each request on each stage of its execution generates an event, which is then pre-processed according to a certain policy and written to a backend. The policy determines what’s recorded and the backends persist the records. You might want to configure the audit log as part of compliance with the CIS (Center for Internet Security) Kubernetes Benchmark controls. The audit log can be enabled by default using the following configuration in cluster.yml: services: kube-api: audit_log: enabled: true When the audit log is enabled, you should be able to see the default values at /etc/kubernetes/auditpolicy.yaml The log backend writes audit events to a file in JSONlines format. You can configure the log audit backend using the following kube-apiserver flags: --audit-log-path specifies the log file path that log backend uses to write audit events. Not specifying this flag disables log backend. - means standard out --audit-log-maxage defined the maximum number of days to retain old audit log files --audit-log-maxbackup defines the maximum number of audit log files to retain --audit-log-maxsize defines the maximum size in megabytes of the audit log file before it gets rotated If your cluster's control plane runs the kube-apiserver as a Pod, remember to mount the hostPath to the location of the policy file and log file, so that audit records are persisted. For example: --audit-policy-file=/etc/kubernetes/audit-policy.yaml \ --audit-log-path=/var/log/audit.log 

API server: Ensure the --authorization-mode argument includes RBAC Turn on Role Based Access Control. Role Based Access Control (RBAC) allows fine-grained control over the operationsthat different entities can perform on different objects in the cluster. It is recommended to use the RBAC authorization mode. Fix - Buildtime Kubernetes apiVersion: v1 kind: Pod metadata: creationTimestamp: null labels: component: kube-apiserver tier: control-plane name: kube-apiserver 

namespace: kube-system

spec:

containers:

- command:

+ - kube-apiserver

+ - --authorization-mode=RBAC,Node

image: gcr.io/google_containers/kube-apiserver-amd64:v1.6.0

livenessProbe:

failureThreshold: 8

httpGet:

host: 127.0.0.1

path: /healthz

port: 6443

scheme: HTTPS

initialDelaySeconds: 15

timeoutSeconds: 15

name: kube-apiserver-should-pass

resources:

requests:

cpu: 250m

volumeMounts:

-mountPath: /etc/kubernetes/

name: k8s

readOnly: true

-mountPath: /etc/ssl/certs

name: certs

-mountPath: /etc/pki

name: pki

hostNetwork: true

volumes:

- hostPath:

path: /etc/kubernetes

name: k8s

- hostPath:

path: /etc/ssl/certs

name: certs

- hostPath:

path: /etc/pki

name: pki

Ensure the --authorization-mode argument includes Node

Remediation: Edit the API server pod specification file /etc/kubernetes/manifests/kubeapiserver.yaml on the master node and set the --authorization-mode parameter to a value that

includes Node.

--authorization-mode=Node,RBAC

Audit:

/bin/ps -ef | grep kube-apiserver | grep -v grep

Expected result:

'Node,RBAC' has 'Node'

Ensure that the --profiling argument is set to false

Remediation: Edit the APIserver pod specification file /etc/kubernetes/manifests/kubeapiserver.yaml on the master node and set the below parameter.

--profiling=false

Audit:

/bin/ps -ef | grep kube-apiserver | grep -v grep

Expected result:

'false' is equal to 'false'

Fix all of the following violations that were found against the Kubelet:-

Ensure the --anonymous-auth argument is set to false.

Remediation: If using a Kubelet config file, edit the file to set authentication: anonymous: enabled

to false. If using executable arguments, edit the kubelet service

file /etc/systemd/system/kubelet.service.d/10-kubeadm.conf on each worker node and set the

below parameter in KUBELET_SYSTEM_PODS_ARGS variable.

--anonymous-auth=false

Based on yoursystem, restart the kubeletservice. For example:

systemctl daemon-reload

systemctl restart kubelet.service

Audit:

/bin/ps -fC kubelet

Audit Config:

/bin/cat /var/lib/kubelet/config.yaml

Expected result:

'false' is equal to 'false'

2) Ensure that the --authorization-mode argument is set to Webhook.

Audit

dockerinspect kubelet | jq -e '.[0].Args[] | match("--authorization-mode=Webhook").string'

Returned Value: --authorization-mode=Webhook

Fix all of the following violations that were found against the ETCD:-

a. Ensure that the --auto-tls argument is not set to true

Do not use self-signed certificates for TLS. etcd is a highly-available key value store used by

Kubernetes deployments for persistent storage of all of its REST API objects. These objects are

sensitive in nature and should not be available to unauthenticated clients. You should enable the

client authentication via valid certificates to secure the access to the etcd service.

Fix - Buildtime

Kubernetes

apiVersion: v1

kind: Pod

metadata:

annotations:

scheduler.alpha.kubernetes.io/critical-pod: ""

Expected result:

'Node,RBAC' has 'Node'

Ensure that the --profiling argument is set to false

Remediation: Edit the APIserver pod specification file /etc/kubernetes/manifests/kubeapiserver.yaml on the master node and set the below parameter.

--profiling=false

Audit:

/bin/ps -ef | grep kube-apiserver | grep -v grep

Expected result:

'false' is equal to 'false'

Fix all of the following violations that were found against the Kubelet:-

Ensure the --anonymous-auth argument is set to false.

Remediation: If using a Kubelet config file, edit the file to set authentication: anonymous: enabled

to false. If using executable arguments, edit the kubelet service

file /etc/systemd/system/kubelet.service.d/10-kubeadm.conf on each worker node and set the

below parameter in KUBELET_SYSTEM_PODS_ARGS variable.

--anonymous-auth=false

Based on yoursystem, restart the kubeletservice. For example:

systemctl daemon-reload

systemctl restart kubelet.service

Audit:

/bin/ps -fC kubelet

Audit Config:

/bin/cat /var/lib/kubelet/config.yaml

Expected result:

'false' is equal to 'false'

2) Ensure that the --authorization-mode argument is set to Webhook.

Audit

dockerinspect kubelet | jq -e '.[0].Args[] | match("--authorization-mode=Webhook").string'

Returned Value: --authorization-mode=Webhook

Fix all of the following violations that were found against the ETCD:-

a. Ensure that the --auto-tls argument is not set to true

Do not use self-signed certificates for TLS. etcd is a highly-available key value store used by

Kubernetes deployments for persistent storage of all of its REST API objects. These objects are

sensitive in nature and should not be available to unauthenticated clients. You should enable the

client authentication via valid certificates to secure the access to the etcd service.

Fix - Buildtime

Kubernetes

apiVersion: v1

kind: Pod

metadata:

annotations:

scheduler.alpha.kubernetes.io/critical-pod: ""

Create a PSP that will prevent the creation of privileged pods in the namespace.

$ cat clusterrole-use-privileged.yaml

---

apiVersion: rbac.authorization.k8s.io/v1

kind: ClusterRole

metadata:

name: use-privileged-psp

rules:

- apiGroups: ['policy']

resources: ['podsecuritypolicies']

verbs: ['use']

resourceNames:

- default-psp

---

apiVersion: rbac.authorization.k8s.io/v1

kind: RoleBinding

metadata:

name: privileged-role-bind

namespace: psp-test

roleRef:

apiGroup: rbac.authorization.k8s.io

kind: ClusterRole

name: use-privileged-psp

subjects:

- kind: ServiceAccount

name: privileged-sa

$ kubectl -n psp-test apply -f clusterrole-use-privileged.yaml

After a few moments, the privileged Pod should be created.

Create a new PodSecurityPolicy named prevent-privileged-policy which prevents the creation of

privileged pods.

apiVersion: policy/v1beta1

kind: PodSecurityPolicy

metadata:

name: example

spec:

privileged: false # Don't allow privileged pods!

# The rest fills in some required fields.

seLinux:

rule: RunAsAny

supplementalGroups:

rule: RunAsAny

runAsUser:

rule: RunAsAny

fsGroup:

rule: RunAsAny

volumes:

- '*'

And create it with kubectl:

kubectl-admin create -f example-psp.yaml

Now, as the unprivileged user, try to create a simple pod:

kubectl-user create -f- <<EOF

apiVersion: v1

kind: Pod

metadata:

name: pause

spec:

containers:

- name: pause

image: k8s.gcr.io/pause

EOF

The output is similar to this:

Error from server (Forbidden): error when creating "STDIN": pods "pause" is forbidden: unable to

validate against any pod security policy: []

Create a new ServiceAccount named psp-sa in the namespace default.

$ cat clusterrole-use-privileged.yaml

---

apiVersion: rbac.authorization.k8s.io/v1

kind: ClusterRole

metadata:

name: use-privileged-psp

rules:

- apiGroups: ['policy']

resources: ['podsecuritypolicies']

verbs: ['use']

resourceNames:

- default-psp

---

apiVersion: rbac.authorization.k8s.io/v1

kind: RoleBinding

metadata:

name: privileged-role-bind

namespace: psp-test

roleRef:

apiGroup: rbac.authorization.k8s.io

kind: ClusterRole

name: use-privileged-psp

subjects:

- kind: ServiceAccount

name: privileged-sa

$ kubectl -n psp-test apply -f clusterrole-use-privileged.yaml

After a few moments, the privileged Pod should be created.

Create a new ClusterRole named prevent-role, which uses the newly created Pod Security Policy

prevent-privileged-policy.

apiVersion: policy/v1beta1

kind: PodSecurityPolicy

metadata:

name: example

spec:

privileged: false # Don't allow privileged pods!

# The rest fills in some required fields.

seLinux:

rule: RunAsAny

supplementalGroups:

rule: RunAsAny

runAsUser:

rule: RunAsAny

fsGroup:

rule: RunAsAny

volumes:

- '*'

And create it with kubectl:

kubectl-admin create -f example-psp.yaml

Now, as the unprivileged user, try to create a simple pod:

kubectl-user create -f- <<EOF

apiVersion: v1

kind: Pod

metadata:

name: pause

spec:

containers:

- name: pause

image: k8s.gcr.io/pause

EOF

The output is similar to this:

Error from server (Forbidden): error when creating "STDIN": pods "pause" is forbidden: unable to

validate against any pod security policy: []

Create a new ClusterRoleBinding named prevent-role-binding, which binds the created ClusterRole

prevent-role to the created SA psp-sa.

apiVersion: rbac.authorization.k8s.io/v1

# This role binding allows "jane" to read pods in the "default" namespace.

# You need to already have a Role named "pod-reader" in that namespace.

kind: RoleBinding

metadata:

name: read-pods

namespace: default

subjects:

# You can specify more than one "subject"

- kind: User

name: jane # "name" is case sensitive

apiGroup: rbac.authorization.k8s.io

roleRef:

# "roleRef" specifies the binding to a Role / ClusterRole

kind: Role #this must be Role or ClusterRole

name: pod-reader # this must match the name of the Role or ClusterRole you wish to bind to

apiGroup: rbac.authorization.k8s.io

apiVersion: rbac.authorization.k8s.io/v1

kind: Role

metadata:

namespace: default

name: pod-reader

rules:

- apiGroups: [""] # "" indicates the core API group

resources: ["pods"]

verbs: ["get", "watch", "list"]

1) Connect to the correct host

ssh cks000028

sudo -i

2) Use the right kubeconfig (safe in exam)

export KUBECONFIG=/etc/kubernetes/admin.conf

3) Open the provided Deployment manifest

vi /home/candidate/finer-sunbeam/lamp-deployment.yaml

4) Edit ONLY the Pod template security settings (add/modify these fields)

Inside:

spec: - > template: - > spec:

4.1 Set container to run as user 20000

Add (or change) under the container securityContext::

securityContext:

runAsUser: 20000

4.2 Make root filesystem read-only

In the SAME container securityContext: ensure:

readOnlyRootFilesystem: true

4.3 Forbid privilege escalation

In the SAME container securityContext: ensure:

allowPrivilegeEscalation: false

✅ The container section should look like this (example — keep your existing image/ports/etc):

spec:

template:

spec:

containers:

- name: < your-container-name >

image: < unchanged >

securityContext:

runAsUser: 20000

readOnlyRootFilesystem: true

allowPrivilegeEscalation: false

If there are multiple containers , apply the same securityContext to each container .

Save and exit:

wq

5) Apply the manifest (updates Deployment - > recreates Pods)

kubectl -n lamp apply -f /home/candidate/finer-sunbeam/lamp-deployment.yaml

6) Wait for rollout

kubectl -n lamp rollout status deployment/lamp-deployment

7) Verify the security settings are live

7.1 Check the Pod is running

kubectl -n lamp get pods -l app=lamp -o wide

(if label differs, just kubectl -n lamp get pods)

7.2 Verify the three fields on a running Pod

Pick the Pod name and run:

POD=$(kubectl -n lamp get pods -o jsonpath= ' {.items[0].metadata.name} ' )

kubectl -n lamp get pod $POD -o jsonpath= ' {.spec.containers[0].securityContext.runAsUser}{ " \n " }{.spec.containers[0].securityContext.readOnlyRootFilesystem}{ " \n " }{.spec.containers[0].securityContext.allowPrivilegeEscalation}{ " \n " } '

Expected output:

20000

true

false

If the pod fails after readOnlyRootFilesystem=true

Don’t change the requirement (task demands it). Usually the app needs writable dirs via volumes, but the task doesn’t ask for that—so only adjust if the manifest already has volumes and just needs these securityContext fields.