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Data Protection →mediumMultiple ChoiceObjective-mapped

SCS-C02 Data Protection Practice Question

This SCS-C02 practice question tests your understanding of data protection. 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 company uses AWS Shield Advanced to protect its web application against DDoS attacks. The application runs behind an Application Load Balancer (ALB) and uses Amazon CloudFront as a CDN. The security team notices that some requests are bypassing CloudFront and hitting the ALB directly. They want to ensure that all traffic goes through CloudFront to benefit from DDoS protection and to enforce encryption in transit. The ALB has a public DNS name and is accessible from the internet. What should the security team do to restrict direct access to the ALB while allowing CloudFront traffic?

A
Use a network ACL to restrict inbound traffic to only CloudFront's IP addresses.
Why wrong: Using a network ACL to restrict inbound traffic to only CloudFront's IP addresses is insufficient because NACLs are stateless and cannot inspect HTTP headers. Additionally, CloudFront's IP ranges change over time, requiring constant updates.
B
Configure CloudFront to add a custom header to requests, and configure the ALB's security group to allow traffic only from CloudFront's IP addresses and that contains the custom header.
This is the correct approach. CloudFront adds a custom header, the ALB's security group restricts by IP, and the ALB's listener rule verifies the header. This ensures only CloudFront-originated requests reach the ALB.
C
Deploy AWS WAF on the ALB with a rule that blocks requests that do not originate from CloudFront.
Why wrong: Deploying AWS WAF on the ALB with a rule that blocks requests not originating from CloudFront is not sufficient because WAF operates at the application layer, and the ALB still accepts connections from the internet. An attacker could bypass WAF by directly connecting to the ALB's IP.
D
Create a security group rule that allows traffic only from CloudFront's IP addresses and denies all other traffic.
Why wrong: Creating a security group rule that allows traffic only from CloudFront's IP addresses is not enough because security groups cannot validate HTTP headers. An attacker could spoof CloudFront IPs or use a different CloudFront distribution to bypass.

Full breakdown with real-world context →

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

✓

Configure CloudFront to add a custom header to requests, and configure the ALB's security group to allow traffic only from CloudFront's IP addresses and that contains the custom header.

Option B is the correct answer. To restrict direct access to the ALB while allowing CloudFront traffic, the security team should configure CloudFront to add a custom header (e.g., X-Origin-Verify) to all requests forwarded to the ALB. Then, configure the ALB's security group to allow inbound traffic only from CloudFront's IP addresses, and configure the ALB's listener rule to require the presence of the custom header. This two-layer approach ensures that only requests originating from CloudFront and containing the expected header are accepted. Option A is incorrect because network ACLs are stateless and cannot inspect HTTP headers; they only filter at the network layer. Option C is incorrect because AWS WAF alone cannot prevent direct connections to the ALB at the network level; it only inspects application-layer traffic after the connection is established. Option D is incorrect because a security group rule allowing only CloudFront's IP addresses does not verify the request originated from CloudFront—an attacker could spoof an IP or use a CloudFront origin feature to bypass.

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.

✗
Use a network ACL to restrict inbound traffic to only CloudFront's IP addresses.
Why it's wrong here
Using a network ACL to restrict inbound traffic to only CloudFront's IP addresses is insufficient because NACLs are stateless and cannot inspect HTTP headers. Additionally, CloudFront's IP ranges change over time, requiring constant updates.
✓
Configure CloudFront to add a custom header to requests, and configure the ALB's security group to allow traffic only from CloudFront's IP addresses and that contains the custom header.
Why this is correct
This is the correct approach. CloudFront adds a custom header, the ALB's security group restricts by IP, and the ALB's listener rule verifies the header. This ensures only CloudFront-originated requests reach the ALB.
Related concept
Standard ACLs match source addresses.
✗
Deploy AWS WAF on the ALB with a rule that blocks requests that do not originate from CloudFront.
Why it's wrong here
Deploying AWS WAF on the ALB with a rule that blocks requests not originating from CloudFront is not sufficient because WAF operates at the application layer, and the ALB still accepts connections from the internet. An attacker could bypass WAF by directly connecting to the ALB's IP.
✗
Create a security group rule that allows traffic only from CloudFront's IP addresses and denies all other traffic.
Why it's wrong here
Creating a security group rule that allows traffic only from CloudFront's IP addresses is not enough because security groups cannot validate HTTP headers. An attacker could spoof CloudFront IPs or use a different CloudFront distribution to bypass.

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.

Visual reference

Quick reference

OSI Model Reference

Layer	Name	PDU	Key Protocols / Devices
7	Application	Data	HTTP, HTTPS, DNS, SMTP, FTP, SSH
6	Presentation	Data	TLS / SSL, JPEG, ASCII encoding
5	Session	Data	NetBIOS, RPC, SIP
4	Transport	Segment / Datagram	TCP, UDP
3	Network	Packet	IP, ICMP, OSPF — Routers
2	Data Link	Frame	Ethernet, Wi-Fi, PPP — Switches, Bridges
1	Physical	Bits	Cables, NICs, Hubs, Repeaters

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.

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FAQ

Questions learners often ask

What does this SCS-C02 question test?

Data Protection — This question tests Data Protection — Standard ACLs match source addresses..

What is the correct answer to this question?

The correct answer is: Configure CloudFront to add a custom header to requests, and configure the ALB's security group to allow traffic only from CloudFront's IP addresses and that contains the custom header. — Option B is the correct answer. To restrict direct access to the ALB while allowing CloudFront traffic, the security team should configure CloudFront to add a custom header (e.g., X-Origin-Verify) to all requests forwarded to the ALB. Then, configure the ALB's security group to allow inbound traffic only from CloudFront's IP addresses, and configure the ALB's listener rule to require the presence of the custom header. This two-layer approach ensures that only requests originating from CloudFront and containing the expected header are accepted. Option A is incorrect because network ACLs are stateless and cannot inspect HTTP headers; they only filter at the network layer. Option C is incorrect because AWS WAF alone cannot prevent direct connections to the ALB at the network level; it only inspects application-layer traffic after the connection is established. Option D is incorrect because a security group rule allowing only CloudFront's IP addresses does not verify the request originated from CloudFront—an attacker could spoof an IP or use a CloudFront origin feature to bypass.

What should I do if I get this SCS-C02 question wrong?

What is the key concept behind this question?

Standard ACLs match source addresses.

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