AWS Certified Security – Specialty (SCS-C02) — Question 184

A company operates a web application that runs on Amazon EC2 instances. The application listens on port 80 and port 443. The company uses an Application Load Balancer (ALB) with AWS WAF to terminate SSL and to forward traffic to the application instances only on port 80.

The ALB is in public subnets that are associated with a network ACL that is named NACL1. The application instances are in dedicated private subnets that are associated with a network ACL that is named NACL2. An Amazon RDS for PostgreSQL DB instance that uses port 5432 is in a dedicated private subnet that is associated with a network ACL that is named NACL3. All the network ACLs currently allow all inbound and outbound traffic.

Which set of network ACL changes will increase the security of the application while ensuring functionality?

Answer options

• A. Make the following changes to NACL3: • Add a rule that allows inbound traffic on port 5432 from NACL2. • Add a rule that allows outbound traffic on ports 1024-65536 to NACL2. • Remove the default rules that allow all inbound and outbound traffic.
• B. Make the following changes to NACL3: • Add a rule that allows inbound traffic on port 5432 from the Cl DR blocks of the application instance subnets. • Add a rule that allows outbound traffic on ports 1024-65536 to the application instance subnets. • Remove the default rules that allow all inbound and outbound traffic.
• C. Make the following changes to NACL2: • Add a rule that allows outbound traffic on port 5432 to the CIDR blocks of the RDS subnets. • Remove the default rules that allow all inbound and outbound traffic.
• D. Make the following changes to NACL2: • Add a rule that allows inbound traffic on port 5432 from the CIDR blocks of the RDS subnets. • Add a rule that allows outbound traffic on port 5432 to the RDS subnets.

Correct answer: B

Explanation

Option B is correct because it specifies allowing inbound traffic on port 5432 from the application instances, which is essential for the RDS to communicate with those instances, while restricting unnecessary traffic. The other options either do not provide the required inbound access for the instances or do not adequately secure the traffic by removing all default permissions.