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Question 1,685 of 1,740

Security and Compliance →hardMultiple ChoiceObjective-mapped

Quick Answer

The correct answer is to switch the WAF web ACL to count mode while tuning the rules, and implement an IAM policy to restrict database access to specific AWS services using the aws:SourceArn condition key. Counting mode is the essential technique to handle WAF SQL injection false positives because it logs and metrics requests that would be blocked without actually blocking them, allowing the security team to analyze traffic patterns and fine-tune rule sensitivity before enforcing the block. This directly addresses the 403 errors for legitimate requests while maintaining protection. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of WAF rule tuning workflows and defense-in-depth for RDS, often appearing as a trap where candidates mistakenly disable rules entirely or add unnecessary infrastructure. A common memory tip is "Count before you cut"—always use counting mode to validate WAF rules before switching to block mode, and pair it with IAM condition keys to lock down database access to only approved services.

DOP-C02 Security and Compliance Practice Question

This DOP-C02 practice question tests your understanding of security and compliance. 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 runs a web application on Amazon ECS with Fargate launch type behind an Application Load Balancer (ALB). The application uses an RDS MySQL database. The security team performed a penetration test and discovered that the application is vulnerable to SQL injection. The development team has deployed a WAF web ACL to the ALB that includes rules to block SQL injection attacks. However, after the deployment, the application started returning 403 errors for legitimate requests, and the security team needs to investigate. The team also wants to ensure that only approved AWS services can access the RDS database. The current security groups are configured with a rule that allows inbound traffic from the ALB security group to the RDS database on port 3306. Which combination of actions should the security team take to resolve the issue and improve the security posture?

Question 1hardmultiple choice

Study the full ACL explanation →

A
Disable the WAF rules that are causing false positives and add network ACLs to block all traffic to the database except from the ALB.
Why wrong: Disabling WAF rules removes protection; network ACLs are stateless and less effective than security groups.
B
Remove the WAF web ACL and rely on security group ingress rules that allow all traffic from the VPC CIDR to the database.
Why wrong: Allowing all VPC traffic to the database is insecure and does not protect against SQL injection.
C
Switch the WAF web ACL to count mode and add a second ALB in front of the database to filter traffic.
Why wrong: A second ALB is unnecessary and adds latency; count mode alone does not block attacks.
D
Switch the WAF web ACL to count mode while tuning the rules, and implement an IAM policy to restrict database access to specific AWS services using the aws:SourceArn condition key.
Count mode allows safe tuning; IAM policies can restrict access to the database from approved services.

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

✓

Switch the WAF web ACL to count mode while tuning the rules, and implement an IAM policy to restrict database access to specific AWS services using the aws:SourceArn condition key.

Option C is correct because counting mode allows the team to see which requests would be blocked without actually blocking them, allowing fine-tuning of the WAF rules. Also, using an IAM policy with condition keys to restrict access to the database from only approved services (like Lambda or specific EC2 instances) adds a layer of defense. Option A is incorrect because disabling the WAF rule is not a security best practice; it would leave the application vulnerable. Option B is incorrect because adding a second ALB does not solve the problem and increases complexity. Option D is incorrect because allowing all traffic to the database from the VPC defeats the purpose of security groups and increases the attack surface.

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

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
Disable the WAF rules that are causing false positives and add network ACLs to block all traffic to the database except from the ALB.
Why it's wrong here
Disabling WAF rules removes protection; network ACLs are stateless and less effective than security groups.
✗
Remove the WAF web ACL and rely on security group ingress rules that allow all traffic from the VPC CIDR to the database.
Why it's wrong here
Allowing all VPC traffic to the database is insecure and does not protect against SQL injection.
✗
Switch the WAF web ACL to count mode and add a second ALB in front of the database to filter traffic.
Why it's wrong here
A second ALB is unnecessary and adds latency; count mode alone does not block attacks.
✓
Switch the WAF web ACL to count mode while tuning the rules, and implement an IAM policy to restrict database access to specific AWS services using the aws:SourceArn condition key.
Why this is correct
Count mode allows safe tuning; IAM policies can restrict access to the database from approved services.
Related concept
CIDR notation defines the prefix length.

Common exam traps

Common exam trap: usable hosts are not the same as total addresses

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

How to think about this question

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.

KKey Concepts to Remember

CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.

TExam Day Tips

Write the block size before choosing the subnet.
Check whether the question asks for hosts, subnets or a specific address range.
Do not confuse /24, /25, /26 and /27 host counts.

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

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 block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DOP-C02 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this DOP-C02 question test?

Security and Compliance — This question tests Security and Compliance — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: Switch the WAF web ACL to count mode while tuning the rules, and implement an IAM policy to restrict database access to specific AWS services using the aws:SourceArn condition key. — Option C is correct because counting mode allows the team to see which requests would be blocked without actually blocking them, allowing fine-tuning of the WAF rules. Also, using an IAM policy with condition keys to restrict access to the database from only approved services (like Lambda or specific EC2 instances) adds a layer of defense. Option A is incorrect because disabling the WAF rule is not a security best practice; it would leave the application vulnerable. Option B is incorrect because adding a second ALB does not solve the problem and increases complexity. Option D is incorrect because allowing all traffic to the database from the VPC defeats the purpose of security groups and increases the attack surface.

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

What is the key concept behind this question?

CIDR notation defines the prefix length.

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