The answer is AWS WAF and AWS Shield Advanced used together. AWS WAF is a web application firewall that allows you to create custom rules to inspect HTTP(S) requests and block common exploits like SQL injection and cross-site scripting (XSS) at the application layer, and it integrates directly with an Application Load Balancer. AWS Shield Advanced complements this by providing enhanced, always-on detection and mitigation against large-scale DDoS attacks that could overwhelm the ALB or underlying EC2 instances. On the AWS Certified Security Specialty SCS-C02 exam, this pairing tests your understanding of layered defense: WAF handles application-layer threats (OWASP Top 10), while Shield Advanced handles volumetric network-layer attacks. A common trap is choosing CloudFront alone, which lacks built-in WAF rules without an attached web ACL, or NACLs, which operate at the subnet level and cannot inspect payload content. Memory tip: think "WAF for the words, Shield for the waves"—WAF filters malicious code in requests, Shield absorbs the flood of traffic.
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 company is deploying a web application on Amazon EC2 instances behind an Application Load Balancer (ALB). The security engineer needs to protect the application from common web exploits such as SQL injection and cross-site scripting. Which TWO services can be used together to achieve this? (Choose TWO.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
AWS Shield Advanced
Option A and D are correct. AWS WAF can be associated with ALB to filter web requests. AWS Shield Advanced provides enhanced protection against DDoS attacks. Option B is wrong because CloudFront itself does not provide WAF rules. Option C is wrong because NACLs are not designed for web application layer filtering. Option E is wrong because GuardDuty is for threat detection, not inline prevention.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Amazon GuardDuty
Why it's wrong here
GuardDuty is a threat detection service, not an inline prevention service.
✓
AWS Shield Advanced
Why this is correct
Shield Advanced provides advanced DDoS protection and integrates with WAF.
Related concept
Standard ACLs match source addresses.
✗
Network ACLs
Why it's wrong here
NACLs operate at the subnet level and do not inspect application layer traffic.
✓
AWS WAF
Why this is correct
WAF can be attached to ALB to inspect and filter web requests.
Related concept
Standard ACLs match source addresses.
✗
Amazon CloudFront
Why it's wrong here
CloudFront is a CDN; it can be used with WAF but not alone for filtering.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related SCS-C02 ACL questions on filtering logic and placement.
Infrastructure Security — This question tests Infrastructure Security — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: AWS Shield Advanced — Option A and D are correct. AWS WAF can be associated with ALB to filter web requests. AWS Shield Advanced provides enhanced protection against DDoS attacks. Option B is wrong because CloudFront itself does not provide WAF rules. Option C is wrong because NACLs are not designed for web application layer filtering. Option E is wrong because GuardDuty is for threat detection, not inline prevention.
What should I do if I get this SCS-C02 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related SCS-C02 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company runs a web application on Amazon EC2 instances behind an Application Load Balancer (ALB). The security team wants to protect the application from common web exploits such as SQL injection and cross-site scripting. Which AWS service should they use?
medium
A.AWS Network Firewall
✓ B.AWS WAF
C.AWS Firewall Manager
D.AWS Shield Advanced
Why B: AWS WAF is a web application firewall that can protect against common web exploits. Option A is correct. Option B is for network firewall. Option C is for DDoS protection at layer 3/4. Option D is for traffic inspection at the network level.
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This SCS-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 SCS-C02 exam.
Question Discussion
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