The answer is eavesdropping on all MQTT communications. This is correct because MQTT without TLS transmits data in plaintext, and subscribing to the wildcard topic ‘#’ captures every message published to the broker, allowing a tester to passively intercept all traffic. On the Certified Ethical Hacker CEH exam, this scenario tests your understanding of IoT protocol vulnerabilities and the difference between passive and active attacks—a common trap is confusing eavesdropping with replay or injection, but since no TLS encryption is present, the tester simply listens without altering data. Remember: no TLS means no confidentiality, so the wildcard ‘#’ is a passive listener’s best friend.
CEH Practice Question: Advanced Topics: Wireless, Cloud, IoT, Cryptography
This CEH practice question tests your understanding of advanced topics: wireless, cloud, iot, cryptography. 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.
An IoT device uses the MQTT protocol without TLS. A security tester connects to the broker and subscribes to all topics using '#'. What is the tester MOST likely able to accomplish?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Eavesdrop on all MQTT communications
MQTT without encryption allows anyone to subscribe to topics. Subscribing to '#' captures all messages, leading to interception of sensitive data. This is a passive eavesdropping attack, not active manipulation like replay or injection.
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.
✗
Perform a denial of service on the broker
Why it's wrong here
Subscribing alone does not cause DoS; a flood of subscriptions might, but that's not described.
✓
Eavesdrop on all MQTT communications
Why this is correct
By subscribing to '#' (wildcard), the tester receives all messages published to the broker, enabling full eavesdropping.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Inject malicious control commands
Why it's wrong here
Injection requires publishing to a topic with proper credentials; subscribing only allows reading.
✗
Replay previously captured messages
Why it's wrong here
Replay requires capturing and re-sending messages, but the immediate action is just subscribing; replay is a separate step.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 practitioner preparing for the CEH exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CEH question in full detail.
Identify which CEH exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Advanced Topics: Wireless, Cloud, IoT, Cryptography — This question tests Advanced Topics: Wireless, Cloud, IoT, Cryptography — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Eavesdrop on all MQTT communications — MQTT without encryption allows anyone to subscribe to topics. Subscribing to '#' captures all messages, leading to interception of sensitive data. This is a passive eavesdropping attack, not active manipulation like replay or injection.
What should I do if I get this CEH question wrong?
Identify which CEH exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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