CS0-003 Vulnerability Management Practice Question
This CS0-003 practice question tests your understanding of vulnerability management. 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.
A mid-sized e-commerce company uses a multi-cloud environment with AWS and Azure. The vulnerability management team performs monthly authenticated scans using a commercial scanner. During the last scan, a critical remote code execution vulnerability (CVE-2023-XXXX) was identified on an EC2 instance running a legacy application. The application owner states that the instance cannot be patched immediately because the patch would break compatibility with a third-party API. The instance has direct internet access and handles PCI data. The CISO wants to reduce risk to an acceptable level within 48 hours. Which course of action should the analyst recommend?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "immediately / without restart"
Why it matters: Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Place the EC2 instance behind a web application firewall (WAF) and restrict inbound access to known IPs using security groups.
Option A is correct because placing the EC2 instance behind a WAF and restricting inbound access to known IPs via security groups provides immediate, compensating controls that reduce the attack surface for the critical RCE vulnerability. Since the instance cannot be patched within 48 hours, this network-layer isolation (WAF filtering malicious payloads, security groups limiting source IPs) aligns with the CISO's risk reduction requirement while maintaining business operations and PCI compliance.
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.
✓
Place the EC2 instance behind a web application firewall (WAF) and restrict inbound access to known IPs using security groups.
Why this is correct
A WAF can mitigate the specific RCE vector, and network restrictions reduce exposure.
Clue confirmation
The clue word "immediately / without restart" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Decommission the instance and remove the legacy application from service immediately.
Why it's wrong here
This would halt PCI data processing, causing business disruption without a migration plan.
✗
Apply the vendor-recommended patch after testing in a dev environment within two weeks.
Why it's wrong here
Two weeks is too slow for a critical vulnerability with PCI data exposure.
✗
Disable TLS 1.0 and enable TLS 1.2 on the instance to reduce the attack surface.
Why it's wrong here
This does not address the RCE vulnerability; it's a separate SSL issue.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the concept that compensating controls (like WAF + security group restrictions) are acceptable for immediate risk reduction when patching is not feasible, and candidates mistakenly choose a delayed patch (Option C) or an irrelevant security fix (Option D) instead of the correct network-layer mitigation.
Detailed technical explanation
How to think about this question
A WAF (e.g., AWS WAF) can inspect HTTP/HTTPS traffic for known RCE payloads (e.g., OWASP CRS rules) and block them before they reach the EC2 instance, while security groups act as a stateful firewall at the instance level, restricting inbound traffic to only trusted IP ranges (e.g., corporate VPN or partner IPs). This layered defense is a classic compensating control under PCI DSS Requirement 6.2, which allows virtual patching via WAF when a vendor patch cannot be applied immediately. In real-world scenarios, organizations often use AWS WAF with rate-based rules and IP sets to block malicious sources while maintaining API compatibility.
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 developer is choosing between AES-256 (symmetric) and RSA-2048 (asymmetric) for encrypting a large file that will be sent to a partner. Symmetric encryption is fast but requires key exchange; asymmetric is slower but solves the key distribution problem. A hybrid approach — encrypt the file with AES, encrypt the AES key with RSA — is standard. Questions like this test whether you understand when each approach applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CS0-003 question in full detail.
Vulnerability Management — This question tests Vulnerability Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Place the EC2 instance behind a web application firewall (WAF) and restrict inbound access to known IPs using security groups. — Option A is correct because placing the EC2 instance behind a WAF and restricting inbound access to known IPs via security groups provides immediate, compensating controls that reduce the attack surface for the critical RCE vulnerability. Since the instance cannot be patched within 48 hours, this network-layer isolation (WAF filtering malicious payloads, security groups limiting source IPs) aligns with the CISO's risk reduction requirement while maintaining business operations and PCI compliance.
What should I do if I get this CS0-003 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: "immediately / without restart". Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.
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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