- A
Configure containerd to use a default seccomp profile that blocks unprivileged user namespaces and restricts kernel modules loading, and apply it to all pods via a mutating admission webhook.
A default seccomp profile that blocks risky syscalls (e.g., those used for kernel module loading, user namespace creation) effectively prevents many container escapes without breaking most workloads. Applying it via a webhook ensures all pods use it.
- B
Enable user namespaces for all containers by setting the 'hostUsers: false' option in the pod spec, which maps container root to a non-root user on the host.
Why wrong: User namespace remapping is a strong security feature but is still in alpha in Kubernetes 1.22 and may not be available in the current cluster version. It also requires runtime support and can cause compatibility issues with host volumes.
- C
Remove the CAP_SYS_ADMIN and CAP_NET_ADMIN capabilities from all containers by setting a default PodSecurityPolicy that drops these capabilities.
Why wrong: While dropping dangerous capabilities is good, this only removes specific capabilities and does not prevent all container escape techniques. Some exploits may not require these capabilities.
- D
Enable AppArmor on all nodes and apply a custom profile that denies all mount and network-related system calls.
Why wrong: AppArmor can help, but a custom profile that denies all mount and network syscalls would likely break many legitimate workloads. Also, AppArmor is not as fine-grained as seccomp for syscall filtering.
CKS System Hardening Practice Question
This CKS practice question tests your understanding of system hardening. 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.
You are a security engineer at a company running a Kubernetes cluster in production. The cluster uses containerd as the container runtime and has been configured with Node Authorizer and NodeRestriction admission controller. Recently, a security audit revealed that several pods running as root have been compromised via container escape vulnerabilities. The audit report recommends hardening the nodes to reduce the attack surface. Specifically, you need to ensure that even if an attacker gains root access inside a container, they cannot execute privileged operations on the host node, such as loading kernel modules, modifying host network settings, or accessing host devices. The cluster runs on Ubuntu 20.04 nodes with Linux kernel 5.4. You have access to modify node-level configurations but must minimize performance impact and avoid breaking existing workloads that rely on standard Linux capabilities. Which of the following actions would most effectively mitigate these risks?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"minimum / minimize"Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
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
Configure containerd to use a default seccomp profile that blocks unprivileged user namespaces and restricts kernel modules loading, and apply it to all pods via a mutating admission webhook.
Option A is correct because seccomp (secure computing mode) can filter system calls at the kernel level, and by configuring containerd to use a default seccomp profile that blocks syscalls related to unprivileged user namespaces (e.g., `clone` with `CLONE_NEWUSER`) and kernel module loading (e.g., `init_module`, `finit_module`), you prevent container escapes from performing privileged host operations. This approach is runtime-level, applies globally without modifying pod specs, and minimizes performance impact since seccomp uses a BPF-based filter that adds negligible overhead.
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.
- ✓
Configure containerd to use a default seccomp profile that blocks unprivileged user namespaces and restricts kernel modules loading, and apply it to all pods via a mutating admission webhook.
Why this is correct
A default seccomp profile that blocks risky syscalls (e.g., those used for kernel module loading, user namespace creation) effectively prevents many container escapes without breaking most workloads. Applying it via a webhook ensures all pods use it.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Enable user namespaces for all containers by setting the 'hostUsers: false' option in the pod spec, which maps container root to a non-root user on the host.
Why it's wrong here
User namespace remapping is a strong security feature but is still in alpha in Kubernetes 1.22 and may not be available in the current cluster version. It also requires runtime support and can cause compatibility issues with host volumes.
- ✗
Remove the CAP_SYS_ADMIN and CAP_NET_ADMIN capabilities from all containers by setting a default PodSecurityPolicy that drops these capabilities.
Why it's wrong here
While dropping dangerous capabilities is good, this only removes specific capabilities and does not prevent all container escape techniques. Some exploits may not require these capabilities.
- ✗
Enable AppArmor on all nodes and apply a custom profile that denies all mount and network-related system calls.
Why it's wrong here
AppArmor can help, but a custom profile that denies all mount and network syscalls would likely break many legitimate workloads. Also, AppArmor is not as fine-grained as seccomp for syscall filtering.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CNCF often tests the misconception that dropping capabilities alone is sufficient for host-level hardening, but the trap here is that capabilities only restrict privileged operations that require them, while seccomp provides syscall-level filtering that can block escape vectors even when the container runs as root.
Detailed technical explanation
How to think about this question
Seccomp profiles in containerd are defined as JSON files that specify allowed or denied syscalls; the default profile in containerd 1.5+ blocks approximately 44 syscalls, including `keyctl`, `add_key`, and `request_key`, but does not block `init_module` or `clone` with `CLONE_NEWUSER` by default. A custom seccomp profile that blocks `init_module`, `finit_module`, `delete_module`, and `clone` with `CLONE_NEWUSER` (while allowing `clone` for normal process creation) effectively prevents kernel module loading and user namespace creation, which are common vectors for container escapes like CVE-2022-0185. In practice, this approach is used by security-hardened distributions such as Flatcar Container Linux and is recommended by the CIS Kubernetes Benchmark.
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 junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
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.
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FAQ
Questions learners often ask
What does this CKS question test?
System Hardening — This question tests System Hardening — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure containerd to use a default seccomp profile that blocks unprivileged user namespaces and restricts kernel modules loading, and apply it to all pods via a mutating admission webhook. — Option A is correct because seccomp (secure computing mode) can filter system calls at the kernel level, and by configuring containerd to use a default seccomp profile that blocks syscalls related to unprivileged user namespaces (e.g., `clone` with `CLONE_NEWUSER`) and kernel module loading (e.g., `init_module`, `finit_module`), you prevent container escapes from performing privileged host operations. This approach is runtime-level, applies globally without modifying pod specs, and minimizes performance impact since seccomp uses a BPF-based filter that adds negligible overhead.
What should I do if I get this CKS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jun 30, 2026
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.
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