Linux Foundation CKS : Certified Kubernetes Security Specialist (CKS)

Correct Answer:

See the Explanation belowExplanation:
1. For Dockerfile: Fix the image version & user name in Dockerfile
2. For mydeployment.yaml : Fix security contexts
Explanation:
[desk@cli] $ vim /home/cert_masters/Dockerfile
FROM ubuntu:latest # Remove this
FROM ubuntu:18.04 # Add this
USER root # Remove this
USER nobody # Add this
RUN apt get install -y lsof=4.72 wget=1.17.1 nginx=4.2
ENV ENVIRONMENT=testing
USER root # Remove this
USER nobody # Add this
CMD ["nginx -d"]

[desk@cli] $ vim /home/cert_masters/mydeployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
creationTimestamp: null
labels:
app: kafka
name: kafka
spec:
replicas: 1
selector:
matchLabels:
app: kafka
strategy: {}
template:
metadata:
creationTimestamp: null
labels:
app: kafka
spec:
containers:
- image: bitnami/kafka
name: kafka
volumeMounts:
- name: kafka-vol
mountPath: /var/lib/kafka
securityContext:
{"capabilities":{"add":["NET_ADMIN"],"drop":["all"]},"privileged": True,"readOnlyRootFilesystem": False, "runAsUser": 65535} # Delete This
{"capabilities":{"add":["NET_ADMIN"],"drop":["all"]},"privileged": False,"readOnlyRootFilesystem": True, "runAsUser": 65535} # Add This resources: {} volumes:
- name: kafka-vol
emptyDir: {}
status: {}
Pictorial View:
[desk@cli] $ vim /home/cert_masters/mydeployment.yaml

Correct Answer:

You can create a "default" isolation policy for a namespace by creating a NetworkPolicy that selects all pods but does not allow any ingress traffic to those pods.
---
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
name: default-deny-ingress
spec:
podSelector: {}
policyTypes:
- Ingress
You can create a "default" egress isolation policy for a namespace by creating a NetworkPolicy that selects all pods but does not allow any egress traffic from those pods.
---
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
name: allow-all-egress
spec:
podSelector: {}
egress:
- {}
policyTypes:
- Egress
Default deny all ingress and all egress traffic
You can create a "default" policy for a namespace which prevents all ingress AND egress traffic by creating the following NetworkPolicy in that namespace.
---
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
name: default-deny-all
spec:
podSelector: {}
policyTypes:
- Ingress
- Egress
This ensures that even pods that aren't selected by any other NetworkPolicy will not be allowed ingress or egress traffic.

Correct Answer:

See the Explanation below for complete solution
Explanation:
Below is the CKS exam style "do-this-exactly" runbook for Q3. It includes the minimal discovery commands (so you don't guess filenames), then the exact lines/blocks to set.
QUESTION 3 - ImagePolicyWebhook (Validating Admission) - Exam Steps
0) SSH + root
ssh cks000002
sudo -i
1) Identify the provided config files (no guessing)
ls -la /etc/kubernetes/bouncer
You are looking for files typically named like:
admission_configuration.yaml (AdmissionConfiguration)
imagepolicywebhook.yaml (ImagePolicyWebhookConfiguration) OR the ImagePolicyWebhook config embedded inside the AdmissionConfiguration kubeconfig (webhook kubeconfig) If unsure which is which, quick peek:
grep -R "ImagePolicyWebhook" -n /etc/kubernetes/bouncer
grep -R "AdmissionConfiguration" -n /etc/kubernetes/bouncer
grep -R "kubeconfig" -n /etc/kubernetes/bouncer
PART A - Reconfigure API Server to enable required admission plugin(s)
2) Edit API server static pod manifest
vi /etc/kubernetes/manifests/kube-apiserver.yaml
2.1 Enable the admission plugin ImagePolicyWebhook
Find the line starting with:
- --enable-admission-plugins=
Ensure ImagePolicyWebhook is included in that comma list.
Example (your list may differ; just add ImagePolicyWebhook):
- --enable-admission-plugins=NodeRestriction,ImagePolicyWebhook
If the flag does not exist, add one line under command::
- --enable-admission-plugins=ImagePolicyWebhook
2.2 Point API server to the provided AdmissionConfiguration
In the same file, ensure this flag exists (use the file in /etc/kubernetes/bouncer that contains AdmissionConfiguration):
- --admission-control-config-file=/etc/kubernetes/bouncer/admission_configuration.yaml If your file is named differently, use the real filename you found in step 1, but keep the flag name exactly --admission-control-config-file.
Save/exit:
:wq
Static pod will restart automatically (kubelet watches the manifest).
Optional quick watch:
docker ps | grep kube-apiserver
# or:
crictl ps | grep kube-apiserver
PART B - Configure ImagePolicyWebhook to deny images on backend failure
3) Edit the ImagePolicyWebhook config
One of these is true on your cluster:
Option 1 (most common in these tasks): ImagePolicyWebhook config is a standalone file Edit the file in /etc/kubernetes/bouncer that contains kind: ImagePolicyWebhookConfiguration:
grep -R "kind: ImagePolicyWebhookConfiguration" -n /etc/kubernetes/bouncer vi /etc/kubernetes/bouncer/<THE_FILE_YOU_FOUND>.yaml Set (or ensure) exactly:
defaultAllow: false
Option 2: ImagePolicyWebhook config is embedded inside AdmissionConfiguration Edit the AdmissionConfiguration file:
vi /etc/kubernetes/bouncer/admission_configuration.yaml
Find the plugin section for ImagePolicyWebhook and ensure the config includes:
defaultAllow: false
✅ Save/exit:
:wq
PART C - Point backend configuration to https://smooth-yak.local/review
4) Edit the webhook kubeconfig to use the scanner endpoint
Find the kubeconfig file referenced by the ImagePolicyWebhook config.
Search for kubeConfigFile:
grep -R "kubeConfigFile" -n /etc/kubernetes/bouncer
Open that kubeconfig path (example name below; yours may differ):
vi /etc/kubernetes/bouncer/kubeconfig
In kubeconfig, set the cluster server exactly:
clusters:
- cluster:
server: https://smooth-yak.local/review
✅ Save/exit:
:wq
PART D - Restart effect (make sure API server picks up config)
Because you already edited /etc/kubernetes/manifests/kube-apiserver.yaml, the API server restarted.
To be safe (and fast), force a restart by "touching" the manifest (no content change needed):
touch /etc/kubernetes/manifests/kube-apiserver.yaml
PART E - Test: apply vulnerable workload and confirm it is denied
5) Use admin kubeconfig (because old kubectl config may break)
export KUBECONFIG=/etc/kubernetes/admin.conf
kubectl get nodes
6) Deploy the test resource (should be DENIED)
kubectl apply -f /home/candidate/vulnerable.yaml
Expected: admission error/denied message.
If it already exists:
kubectl delete -f /home/candidate/vulnerable.yaml
kubectl apply -f /home/candidate/vulnerable.yaml
PART F - Verify the scanner was called (log check)
7) Check scanner access log
tail -n 50 /var/log/nginx/access_log
You should see requests hitting /review.
Quick "what to check if it doesn't deny"
Run these in order:
Confirm API server flags:
grep -n "enable-admission-plugins" /etc/kubernetes/manifests/kube-apiserver.yaml grep -n "admission-control-config-file" /etc/kubernetes/manifests/kube-apiserver.yaml Confirm deny-on-failure:
grep -R "defaultAllow" -n /etc/kubernetes/bouncer
Must show:
defaultAllow: false
Confirm endpoint:
grep -R "server: https://smooth-yak.local/review" -n /etc/kubernetes/bouncer API server logs (docker runtime):
docker ps | grep kube-apiserver
docker logs $(docker ps -q --filter name=kube-apiserver) --tail 80
If you paste the output of:
ls -/etc/kubernetes/bouncer
grep -R "kind: AdmissionConfiguration" -n /etc/kubernetes/bouncer
grep -R "ImagePolicyWebhook" -n /etc/kubernetes/bouncer

Correct Answer:

See the Explanation belowExplanation:

Correct Answer:

FROM debian:latest
MAINTAINER [email protected]
# 1 - RUN
RUN apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -yq apt-utils RUN DEBIAN_FRONTEND=noninteractive apt-get install -yq htop RUN apt-get clean
# 2 - CMD
#CMD ["htop"]
#CMD ["ls", "-l"]
# 3 - WORKDIR and ENV
WORKDIR /root
ENV DZ version1
$ docker image build -t bogodevops/demo .
Sending build context to Docker daemon 3.072kB
Step 1/7 : FROM debian:latest
---> be2868bebaba
Step 2/7 : MAINTAINER [email protected]
---> Using cache
---> e2eef476b3fd
Step 3/7 : RUN apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -yq apt-utils
---> Using cache
---> 32fd044c1356
Step 4/7 : RUN DEBIAN_FRONTEND=noninteractive apt-get install -yq htop
---> Using cache
---> 0a5b514a209e
Step 5/7 : RUN apt-get clean
---> Using cache
---> 5d1578a47c17
Step 6/7 : WORKDIR /root
---> Using cache
---> 6b1c70e87675
Step 7/7 : ENV DZ version1
---> Using cache
---> cd195168c5c7
Successfully built cd195168c5c7
Successfully tagged bogodevops/demo:latest