AWS Certified Security – Specialty — Question 236

A company deployed an Amazon EC2 instance to a VPC on AWS. A recent alert indicates that the EC2 instance is receiving a suspicious number of requests over an open TCP port from an external source. The TCP port remains open for long periods of time.
The company's security team needs to stop all activity to this port from the external source to ensure that the EC2 instance is not being compromised. The application must remain available to other users.
Which solution will meet these requirements?

Answer options

• A. Update the network ACL that is attached to the subnet that is associated with the EC2 instance. Add a Deny statement for the port and the source IP addresses.
• B. Update the elastic network interface security group that is attached to the EC2 instance to remove the port from the inbound rule list.
• C. Update the elastic network interface security group that is attached to the EC2 instance by adding a Deny entry in the inbound list for the port and the source IP addresses.
• D. Create a new network ACL for the subnet. Deny all traffic from the EC2 instance to prevent data from being removed.

Correct answer: A

Explanation

The correct answer is A because modifying the network ACL allows for a specific Deny rule to block traffic from the external source on that port while maintaining overall access for other users. Option B incorrectly suggests removing the port from the security group, which could impact other legitimate traffic. Option C is invalid since security groups do not support Deny rules, and D would unnecessarily block all traffic from the EC2 instance, which is not the desired outcome.