CLF-C02 Security and Compliance Practice Question
A company runs a public-facing e-commerce website on Amazon EC2 instances behind an Application Load Balancer (ALB). The security team has discovered that attackers are attempting SQL injection attacks through the website's search feature. The company wants to use a managed AWS service to inspect incoming HTTP requests and block these malicious payloads before they reach the application. Which AWS service should the company use?
⚠ Common exam trap
Many candidates confuse AWS Shield (which protects against DDoS at Layer 3/4) with AWS WAF (which protects against application-layer attacks like SQL injection), leading them to choose Shield Standard instead of WAF.
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
✓
AWS WAF
AWS WAF is a managed web application firewall that allows you to create rules to inspect HTTP/HTTPS requests and block common attack patterns, such as SQL injection and cross-site scripting. By associating a WAF web ACL with the Application Load Balancer, the company can filter incoming traffic and block malicious payloads before they reach the EC2 instances.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
AWS Shield Standard
Why it's wrong here
AWS Shield Standard provides always-on protection against common DDoS attacks at the network and transport layer, but it does not inspect application-layer content like SQL injection payloads. It cannot block or filter specific HTTP requests.
When this WOULD be correct
A company wants to protect its EC2 instances from common DDoS attacks (e.g., SYN floods, UDP reflection) at no additional cost. AWS Shield Standard is automatically enabled and would be the correct answer.
- ✓
AWS WAF
Why this is correct
AWS WAF is a web application firewall that inspects HTTP and HTTPS requests and can block common threats such as SQL injection and cross-site scripting. It integrates directly with Application Load Balancers, Amazon CloudFront, and API Gateway, making it the correct service for this use case.
- ✗
Network ACLs
Why it's wrong here
Network ACLs are stateless, subnet-level filters that allow or deny traffic based solely on L3/L4 attributes such as source/destination IP, port, and protocol. They cannot inspect the payload of an HTTP request, so SQL injection strings embedded in a URI or body would pass through unnoticed. Additionally, because they are stateless, they require separate inbound and outbound rules and provide no session awareness, making them unsuitable for blocking application-layer attacks. To detect and block SQL injection or XSS, you need a web application firewall like AWS WAF that analyzes request content.
When this WOULD be correct
A company needs to block traffic from a specific IP range at the subnet boundary to reduce load on the application layer. Network ACLs would be the correct choice because they provide stateless filtering at the VPC subnet level.
- ✗
Amazon GuardDuty
Why it's wrong here
Amazon GuardDuty is a threat detection service that continuously monitors for malicious activity and unauthorized behavior using machine learning and threat intelligence. It can detect SQL injection attempts in logs, but it does not actively block the requests; it only generates alerts.
When this WOULD be correct
A company wants to detect potential security threats across AWS accounts and workloads by analyzing VPC Flow Logs, DNS logs, and CloudTrail events, and receive alerts about suspicious activity such as compromised instances or reconnaissance attempts.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The CLF-C02 exam frequently reuses these exact scenarios with slightly different constraints.
✓AWS WAFCorrect answer▾
Why this is correct
AWS WAF is a web application firewall that inspects HTTP and HTTPS requests and can block common threats such as SQL injection and cross-site scripting. It integrates directly with Application Load Balancers, Amazon CloudFront, and API Gateway, making it the correct service for this use case.
✗AWS Shield StandardWrong answer — click to see why▾
Why this is wrong here
AWS Shield Standard provides DDoS protection but does not inspect application-layer payloads like SQL injection strings; it only mitigates volumetric attacks.
★ When this WOULD be the correct answer
A company wants to protect its EC2 instances from common DDoS attacks (e.g., SYN floods, UDP reflection) at no additional cost. AWS Shield Standard is automatically enabled and would be the correct answer.
Why candidates choose this
Candidates may confuse 'security' broadly with 'attack protection' and assume Shield covers all attack types, including application-layer threats like SQL injection.
✗Network ACLsWrong answer — click to see why▾
Why this is wrong here
Network ACLs are stateless and operate at the subnet level, filtering traffic based on IP addresses, ports, and protocols. They cannot inspect application-layer payloads like SQL injection attempts.
★ When this WOULD be the correct answer
A company needs to block traffic from a specific IP range at the subnet boundary to reduce load on the application layer. Network ACLs would be the correct choice because they provide stateless filtering at the VPC subnet level.
Why candidates choose this
Candidates may confuse network-layer filtering with application-layer inspection, assuming that any security control at the network perimeter can block SQL injection attacks.
✗Amazon GuardDutyWrong answer — click to see why▾
Why this is wrong here
Amazon GuardDuty is a threat detection service that monitors for malicious activity and unauthorized behavior, but it does not actively inspect and block HTTP requests at the application layer like a web application firewall. It cannot prevent SQL injection attacks in real-time.
★ When this WOULD be the correct answer
A company wants to detect potential security threats across AWS accounts and workloads by analyzing VPC Flow Logs, DNS logs, and CloudTrail events, and receive alerts about suspicious activity such as compromised instances or reconnaissance attempts.
Why candidates choose this
Candidates may confuse GuardDuty's threat detection capabilities with active request filtering, assuming it can block attacks because it identifies malicious patterns, but it is a detection-only service without inline prevention.
Analysis generated from the official CLF-C02blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CLF-C02 practice question is part of Courseiva's free Amazon Web Services 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 CLF-C02 exam.