CS0-003 Security Operations Practice Question
A security analyst is investigating an alert from AWS GuardDuty that indicates an EC2 instance is communicating with a known malicious IP address on port 4444. The analyst checks the VPC Flow Logs and confirms the traffic. Which of the following is the most appropriate immediate action?
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
✓
Apply a restrictive security group to isolate the instance
Isolating the EC2 instance by applying a restrictive security group stops the malicious communication and allows further investigation.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Create a new IAM role for the instance
Why it's wrong here
Modifying or replacing the IAM role associated with an EC2 instance only alters its AWS API permissions via the Instance Metadata Service. It does not block active network connections, stop outbound malicious traffic, or isolate the instance's network interface from the internet.
- ✓
Apply a restrictive security group to isolate the instance
Why this is correct
Applying an isolation security group with no inbound or outbound rules immediately cuts off network communication at the hypervisor level. This effectively contains the threat and prevents further data exfiltration or command-and-control traffic while preserving the volatile memory and disk state of the EC2 instance for forensic analysis.
- ✗
Terminate the EC2 instance immediately
Why it's wrong here
Terminating the EC2 instance permanently deletes volatile RAM and, depending on the EBS volume configuration, may also delete the root storage volume. This action destroys critical forensic evidence, such as running processes, network connections, and memory artifacts, which are essential for a thorough incident investigation.
- ✗
Update the route table to blackhole the traffic
Why it's wrong here
Modifying a VPC route table to blackhole traffic affects the entire subnet associated with that route table, potentially disrupting legitimate business traffic for other healthy instances. Additionally, route tables cannot easily filter traffic to specific malicious external IPs without complex configurations, making it an imprecise and disruptive containment method compared to security group isolation.
Go deeper
Related to this question
Learn chapter
NetFlow and Traffic Flow Analysis
Key term
Alert
An alert is a notification that something unusual or potentially harmful has happened in a computer system or network.
Key term
VPC Flow Logs
A feature that captures information about the IP traffic going to and from network interfaces in a Virtual Private Cloud (VPC).
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CS0-004 practice question is part of Courseiva's free CompTIA 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 CS0-004 exam.