The correct answer is to restrict registry write access to the CI/CD service account and enable image signature verification via an admission controller in Kubernetes. This solution directly addresses the two root causes: by locking down registry write permissions, you prevent developers from pushing unsigned images outside the pipeline, and by implementing an admission controller—such as ImagePolicyWebhook or a tool like Cosign with OCI signatures—you enforce signature verification at the cluster level, ensuring only signed and scanned container images are deployed. On the CompTIA SecurityX CAS-004 exam, this scenario tests your understanding of defense-in-depth for CI/CD container image signing and scanning, where a common trap is focusing only on registry controls while ignoring Kubernetes-side enforcement. Remember that pipeline security requires both a gate at the registry (who can push) and a gate at the cluster (what can run). A useful memory tip is "Push lock, pull check"—restrict who pushes, then verify what gets pulled.
CAS-004 Security Engineering Practice Question
This CAS-004 practice question tests your understanding of security engineering. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company's development team uses a CI/CD pipeline hosted in a public cloud. The pipeline builds container images, pushes them to a private registry, and deploys them to a Kubernetes cluster. A security engineer must ensure that only signed and vulnerability-scanned images are deployed. The engineer has configured the registry to require signatures and the CI/CD pipeline to scan images. However, deployments are still failing because unsigned images are being pulled. The engineer discovers that developers can push images directly to the registry bypassing the CI/CD pipeline and that Kubernetes nodes can pull images without signature verification. Which of the following should the engineer implement to enforce image signing and scanning?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Restrict registry write access to the CI/CD service account and enable image signature verification via admission controller in Kubernetes.
Option C is correct because it addresses both root causes: restricting registry write access to only the CI/CD service account prevents developers from bypassing the pipeline, and enabling image signature verification via an admission controller (e.g., using Kubernetes ImagePolicyWebhook or a tool like Cosign with OCI signatures) ensures that only signed and scanned images are allowed to run in the cluster. This combination enforces the security policy at both the registry and the cluster level, closing the gaps identified in the scenario.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Implement a manual approval step in the pipeline for each deployment.
Why it's wrong here
Manual approval does not enforce signing or prevent direct registry pushes.
✗
Use network policies to block all outbound traffic from developer workstations to the container registry.
Why it's wrong here
Does not enforce signature verification and may break legitimate access.
✓
Restrict registry write access to the CI/CD service account and enable image signature verification via admission controller in Kubernetes.
Why this is correct
Restricts pushes to authorized accounts and verifies signatures at deployment time.
Related concept
Read the scenario before looking for a memorised answer.
✗
Configure the CI/CD pipeline to perform vulnerability scanning after every build.
Why it's wrong here
Scanning does not prevent unsigned images from being deployed.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often focus only on the CI/CD pipeline (e.g., scanning or approvals) and overlook the need to restrict direct registry access and enforce signature verification at the cluster level, which are the two distinct vulnerabilities described in the scenario.
Detailed technical explanation
How to think about this question
Under the hood, image signing typically uses cryptographic signatures (e.g., with Cosign or Notary) stored as OCI artifacts in the registry, and Kubernetes admission controllers like ImagePolicyWebhook or OPA Gatekeeper can validate these signatures before admitting a pod. A subtle behavior is that the admission controller must be configured to reject unsigned images by default, and the registry must enforce that only signed images are accepted (e.g., via tag immutability or signature verification hooks). In a real-world scenario, a misconfigured admission controller that only logs violations instead of rejecting them would still allow unsigned images to run, which is why the 'enforce' aspect is critical.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security Engineering — This question tests Security Engineering — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Restrict registry write access to the CI/CD service account and enable image signature verification via admission controller in Kubernetes. — Option C is correct because it addresses both root causes: restricting registry write access to only the CI/CD service account prevents developers from bypassing the pipeline, and enabling image signature verification via an admission controller (e.g., using Kubernetes ImagePolicyWebhook or a tool like Cosign with OCI signatures) ensures that only signed and scanned images are allowed to run in the cluster. This combination enforces the security policy at both the registry and the cluster level, closing the gaps identified in the scenario.
What should I do if I get this CAS-004 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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