CS0-003 Security Operations Practice Question
An analyst is investigating an alert from AWS GuardDuty that indicates an EC2 instance is communicating with a known malicious IP address. The analyst checks the VPC Flow Logs and confirms the communication. What is the next best step in the investigation?
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
✓
Isolate the EC2 instance from the network.
Since the EC2 instance is compromised, isolating it (e.g., by modifying security groups or stopping the instance) prevents further malicious activity while preserving evidence.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Run a vulnerability scan on the instance.
Why it's wrong here
Running a vulnerability scan is a detective control designed to identify security weaknesses, not an active containment measure. Initiating a scan during an active compromise consumes valuable time and system resources without stopping the ongoing malicious outbound communication. Containment must always precede vulnerability assessment in the incident response lifecycle.
- ✗
Ignore the alert because GuardDuty often produces false positives.
Why it's wrong here
Dismissing a GuardDuty alert regarding communication with a known malicious IP address violates standard incident response triage procedures. While false positives can occur, high-severity threat intelligence matches require immediate validation and containment. Ignoring such alerts leaves the cloud environment vulnerable to data exfiltration, lateral movement, or further compromise.
- ✓
Isolate the EC2 instance from the network.
Why this is correct
Isolating the EC2 instance by modifying its security groups to block all inbound and outbound traffic is the primary containment step. This action immediately halts malicious command-and-control (C2) communication or data exfiltration. Crucially, network isolation preserves the volatile memory (RAM) and disk state of the running instance for subsequent forensic analysis.
- ✗
Delete the EC2 instance immediately.
Why it's wrong here
Terminating the EC2 instance immediately is an overreaction that permanently destroys critical forensic evidence, such as volatile memory contents, active network connections, and temporary log files. Without this data, root-cause analysis is impossible, preventing the organization from identifying how the breach occurred. Proper containment must preserve the system state for investigation before eradication.
Go deeper
Related to this question
Learn chapter
Splunk SPL Queries for Security Analysts
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.