Quick Answer
The answer is AWS WAF. This service is the correct choice because it operates at the application layer (Layer 7) of the OSI model, allowing it to inspect HTTP/HTTPS requests for malicious patterns like SQL injection and cross-site scripting, while also providing geo-matching rules to block or allow traffic from specific countries. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of where different security services apply—AWS Shield Advanced handles volumetric DDoS attacks, not application-layer exploits, and both Network ACLs and Security Groups lack the deep packet inspection needed for web-specific threats. A common trap is confusing WAF with Shield Advanced, so remember: WAF is for web exploits and geo-blocking, Shield is for DDoS. Memory tip: "WAF watches the web, Shield stops the flood."
This SCS-C02 practice question tests your understanding of infrastructure security. 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 startup is building a web application on AWS. They have an Application Load Balancer (ALB) in front of EC2 instances in an Auto Scaling group. They want to protect the application from common web exploits like SQL injection and cross-site scripting. They also need to allow only traffic from certain geographic regions. Which AWS service should they use to achieve these requirements?
AWS WAF
WAF can block SQL injection, XSS, and geo-match rules.
AWS Shield Advanced
Why wrong: Shield Advanced provides DDoS protection, not application layer filtering.
Security groups on the ALB
Why wrong: Security groups are stateful but operate at network layer, not application layer.
Network ACLs on the ALB subnets
Why wrong: NACLs are stateless and operate at layer 3/4, not application layer.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
AWS WAF
Option B is correct because AWS WAF can block SQL injection, XSS, and geo-based requests. Option A is wrong because AWS Shield Advanced is for DDoS protection. Option C is wrong because Network ACLs are stateless and cannot inspect application layer. Option D is wrong because Security Groups are stateful but cannot inspect application layer.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
AWS WAF
Why this is correct
WAF can block SQL injection, XSS, and geo-match rules.
Related concept
CIDR notation defines the prefix length.
AWS Shield Advanced
Why it's wrong here
Shield Advanced provides DDoS protection, not application layer filtering.
Security groups on the ALB
Why it's wrong here
Security groups are stateful but operate at network layer, not application layer.
Network ACLs on the ALB subnets
Why it's wrong here
NACLs are stateless and operate at layer 3/4, not application layer.
Common exam traps
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Infrastructure Security — This question tests Infrastructure Security — CIDR notation defines the prefix length..
The correct answer is: AWS WAF — Option B is correct because AWS WAF can block SQL injection, XSS, and geo-based requests. Option A is wrong because AWS Shield Advanced is for DDoS protection. Option C is wrong because Network ACLs are stateless and cannot inspect application layer. Option D is wrong because Security Groups are stateful but cannot inspect application layer.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
CIDR notation defines the prefix length.
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Last reviewed: Jun 20, 2026
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.
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