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.
Exhibit
Refer to the exhibit.
```
apiVersion: v1
kind: Pod
metadata:
name: test-pod
spec:
containers:
- name: test
image: alpine
securityContext:
runAsUser: 1000
runAsGroup: 3000
allowPrivilegeEscalation: false
capabilities:
drop: ["ALL"]
```
A pod manifest is shown. What security issue remains in this configuration?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The container has a writable root filesystem
Option B is correct because the pod manifest does not set `readOnlyRootFilesystem: true` in the container's security context. Without this setting, the container's root filesystem is writable by default, allowing an attacker who compromises the container to modify binaries, configuration files, or write malicious scripts to persistent storage, thereby increasing the attack surface and potentially enabling persistence or privilege escalation.
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.
✗
The container runs as root (user 0)
Why it's wrong here
runAsUser is set to 1000, not root.
✓
The container has a writable root filesystem
Why this is correct
There is no readOnlyRootFilesystem: true, so the root filesystem is writable, which is a security risk.
Related concept
Read the scenario before looking for a memorised answer.
✗
The container has dangerous capabilities
Why it's wrong here
All capabilities are dropped.
✗
The container can escalate privileges
Why it's wrong here
allowPrivilegeEscalation is set to false.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume the default security context is secure, but Cisco tests the specific omission of `readOnlyRootFilesystem: true` as a distinct hardening requirement, even when other settings like `runAsNonRoot: true` are present.
Detailed technical explanation
How to think about this question
The `readOnlyRootFilesystem` security context setting mounts the container's root filesystem as read-only, enforced by the kernel's mount namespace. Even with a writable rootfs, an attacker could use `chmod` or `echo` to overwrite critical files like `/etc/passwd` or inject a cron job; in real-world scenarios, this is a common vector for container escape via kernel exploits (e.g., CVE-2019-5736) that require writing to the host filesystem through a writable overlay. The default behavior in Docker and containerd is a writable rootfs, making this a frequent oversight in hardened configurations.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CKS question in full detail.
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: The container has a writable root filesystem — Option B is correct because the pod manifest does not set `readOnlyRootFilesystem: true` in the container's security context. Without this setting, the container's root filesystem is writable by default, allowing an attacker who compromises the container to modify binaries, configuration files, or write malicious scripts to persistent storage, thereby increasing the attack surface and potentially enabling persistence or privilege escalation.
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.
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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