The correct answer is to implement client certificate authentication on AWS IoT Core and revoke any unregistered client IDs because the attack exploits weak MQTT authentication, allowing an adversary to inject malicious data by spoofing sensor client IDs. In MQTT, the broker typically trusts any client that presents a valid client ID unless certificate-based mutual TLS is enforced; without it, an attacker can publish arbitrary payloads to topics, which then flow into S3 and DynamoDB as unauthorized PUT and write spikes. On the Certified Ethical Hacker CEH exam, this scenario tests your understanding of IoT attack surfaces and the principle of device identity verification—a common trap is to focus on network-layer fixes like VPN hardening when the real vulnerability is at the application layer. Remember the mnemonic “MQTT Must Trust TLS” to recall that MQTT brokers require client certificates to secure IoT sensors against unauthorized data injection.
CEH Wireless, IoT and Cloud Security Practice Question
This CEH practice question tests your understanding of wireless, iot and cloud security. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 the security lead for a multinational corporation that uses a hybrid cloud architecture with AWS and on-premises data centers. The company recently deployed a fleet of IoT sensors in a remote factory to monitor equipment. These sensors communicate via MQTT to an AWS IoT Core endpoint, which forwards data to an S3 bucket and a DynamoDB table. The factory network is isolated but has a site-to-site VPN to the corporate HQ. Over the past week, the S3 bucket has experienced an unusual number of PUT requests from an IP address that resolves to a known malicious host. The DynamoDB table shows write spikes at odd hours. The MQTT broker logs indicate that some sensors are publishing data with invalid client IDs. Meanwhile, the VPN logs show no anomalies. You need to identify the likely attack vector and recommend a course of action. Which of the following is the BEST course of action?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Implement client certificate authentication on AWS IoT Core and revoke any unregistered client IDs.
Option B is correct because the attack exploits weak authentication on MQTT connections to AWS IoT Core. By implementing client certificate authentication, you ensure only registered devices with valid X.509 certificates can publish data, directly blocking the malicious PUT requests and write spikes. Revoking unregistered client IDs eliminates the invalid client IDs observed in the MQTT broker logs, closing the primary attack vector without disrupting legitimate sensor traffic.
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.
✗
Disable the site-to-site VPN and require all traffic to go through a bastion host.
Why it's wrong here
The VPN is not the source; this would disrupt legitimate traffic.
✓
Implement client certificate authentication on AWS IoT Core and revoke any unregistered client IDs.
Why this is correct
This ensures only authenticated sensors can publish, blocking the malicious PUT requests.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Move the S3 bucket and DynamoDB table to the on-premises data center to reduce cloud exposure.
Why it's wrong here
This is a drastic change and does not address the root cause of unauthenticated publishes.
✗
Replace all IoT sensors with new ones that have firmware-level encryption.
Why it's wrong here
The sensors themselves are not compromised; the issue is at the cloud endpoint.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates focus on network-level controls (VPN, bastion hosts) or data relocation, missing that the attack exploits weak IoT device authentication at the application layer, which requires identity-based controls like client certificates.
Detailed technical explanation
How to think about this question
AWS IoT Core supports mutual TLS authentication where each device presents a unique X.509 certificate; the broker verifies the certificate against a registered CA. MQTT client IDs are used for session state, but without certificate-based auth, any client can claim any ID, enabling spoofing. In real-world attacks, adversaries often scan for open MQTT ports (1883 or 8883) and publish malicious payloads to trigger cloud-side processing, as seen in the S3 PUT and DynamoDB write spikes.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CEH question in full detail.
Wireless, IoT and Cloud Security — This question tests Wireless, IoT and Cloud Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Implement client certificate authentication on AWS IoT Core and revoke any unregistered client IDs. — Option B is correct because the attack exploits weak authentication on MQTT connections to AWS IoT Core. By implementing client certificate authentication, you ensure only registered devices with valid X.509 certificates can publish data, directly blocking the malicious PUT requests and write spikes. Revoking unregistered client IDs eliminates the invalid client IDs observed in the MQTT broker logs, closing the primary attack vector without disrupting legitimate sensor traffic.
What should I do if I get this CEH 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". 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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