- A
ENV
ENV sets environment variables that can contain hardcoded secrets.
- B
EXPOSE
Why wrong: EXPOSE documents ports.
- C
RUN
Why wrong: RUN executes commands, but secrets are more likely in ENV or ARG.
- D
FROM
Why wrong: FROM specifies base image.
Question 602 of 997
Which Dockerfile Instruction Often Contains Hardcoded Secrets?
This CKS practice question tests your understanding of supply chain security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 security best practice for Dockerfiles is to avoid hardcoded secrets. Which Dockerfile instruction is MOST likely to contain a hardcoded secret?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"best"Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
✓
ENV
The ENV instruction in a Dockerfile is used to set environment variables, which are often used to store sensitive data like API keys, passwords, or tokens. Hardcoding secrets in ENV is a security risk because the values persist in the image layers and can be extracted by anyone with access to the image, violating the principle of least privilege and secret management best practices.
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.
- ✓
ENV
Why this is correct
ENV sets environment variables that can contain hardcoded secrets.
Clue confirmation
The clue words "best", "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
EXPOSE
Why it's wrong here
EXPOSE documents ports.
- ✗
RUN
Why it's wrong here
RUN executes commands, but secrets are more likely in ENV or ARG.
- ✗
FROM
Why it's wrong here
FROM specifies base image.
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common pitfall is assuming that RUN is the most likely instruction to contain secrets because it executes commands, but the trap is that ENV is the instruction where secrets are most commonly and persistently hardcoded as environment variables, making it the primary security concern in Dockerfiles.
Trap categories for this question
Command / output trap
RUN executes commands, but secrets are more likely in ENV or ARG.
Detailed technical explanation
How to think about this question
Under the hood, each Dockerfile instruction creates a new layer in the image. When a secret is set via ENV, it is stored in the image metadata and can be retrieved using `docker history` or by inspecting the image layers. A real-world scenario is a CI/CD pipeline that builds an image with a hardcoded database password in ENV; anyone pulling that image can extract the password, leading to a supply chain compromise. Best practice is to use Docker build secrets (e.g., `--secret` flag) or external secret stores like HashiCorp Vault.
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.
- →
Supply Chain Security — study guide chapter
Learn the concepts, then practise the questions
- →
Supply Chain Security practice questions
Targeted practice on this topic area only
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Certified Kubernetes Security Specialist CKS study guide
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FAQ
Questions learners often ask
What does this CKS question test?
Supply Chain Security — This question tests Supply Chain Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: ENV — The ENV instruction in a Dockerfile is used to set environment variables, which are often used to store sensitive data like API keys, passwords, or tokens. Hardcoding secrets in ENV is a security risk because the values persist in the image layers and can be extracted by anyone with access to the image, violating the principle of least privilege and secret management best practices.
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: "best", "most likely". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 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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