CKS System Hardening Practice Question
A security engineer wants to enforce that all containers in a namespace run without any unnecessary Linux capabilities, dropping all capabilities by default and only adding back what is needed. Which Pod Security Standard should be applied to that namespace using PodSecurity admission?
⚠ Common exam trap
CNCF often tests the misconception that 'Baseline' is sufficient for strict capability control, but Baseline only blocks known dangerous capabilities (e.g., `CAP_SYS_ADMIN`) and does not require dropping all capabilities, so candidates must recognize that only Restricted enforces a full drop-all policy.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Restricted
The Restricted Pod Security Standard is the most stringent profile, which enforces dropping all capabilities by default and only allowing those explicitly required. It sets `securityContext.capabilities.drop: ["ALL"]` and restricts `allowedCapabilities` to an empty set, ensuring containers run with minimal Linux capabilities. This directly matches the requirement to drop all capabilities and add back only what is needed.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Privileged
Why it's wrong here
The privileged level is the most permissive Pod Security Standard: it permits privileged containers, host namespace sharing, and grants every Linux capability to processes. It imposes no requirement to drop capabilities, run as a non-root user, or disable privilege escalation. Choosing this option would place pods in a maximally unrestricted security context, directly contradicting the security engineer's goal of a minimal capability set.
- ✗
Custom
Why it's wrong here
Pod Security Standards define exactly three built-in levels — privileged, baseline, and restricted — so 'Custom' is not a valid PSS level. While organizations can create custom admission policies beyond the standards, the question specifically asks which Pod Security Standard enforces dropping all capabilities. Since no such custom level exists in the PSS framework, this response cannot satisfy the requirement.
- ✗
Baseline
Why it's wrong here
The baseline level is a moderately restrictive policy that prevents known privilege escalations by forbidding privileged containers and host namespace sharing, but it intentionally allows each container to retain the runtime's default Linux capability set. It does not require dropping ALL capabilities, nor does it enforce allowPrivilegeEscalation: false. Therefore, baseline only partially hardens the environment and fails the explicit requirement to start from an empty capability set.
- ✓
Restricted
Why this is correct
The restricted level is the Pod Security Standard that directly fulfills the requirement: it mandates that every container set securityContext.capabilities.drop to ALL and permits adding back only the NET_BIND_SERVICE capability when required, such as for binding to low-numbered ports. It also enforces runAsNonRoot, a non-zero runAsUser, allowPrivilegeEscalation: false, and the RuntimeDefault seccomp profile. This capability-denylist-plus-allowlist approach matches the security engineer's intent to eliminate all non-essential capabilities.
Go deeper
Related to this question
Learn chapter
Supply Chain Security: Policy Enforcement and Admission Controllers
Key term
Admission Controllers
Admission controllers are plugins that intercept and process requests to the Kubernetes API server after authentication and authorization, but before the request is persisted, allowing policies to be enforced on objects being created, modified, or deleted.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CKS practice question is part of Courseiva's free CNCF certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CKS exam.