The correct answer is to analyze both EC2 instance OS logs (such as /var/log/secure or /var/log/auth.log) and CloudTrail logs for API calls that launched the instance. OS logs capture the actual commands executed on the compromised instance, which is essential for tracing the source of the outbound DDoS attack, while CloudTrail logs reveal who launched the instance and what IAM permissions were used, providing the broader context of the compromise. On the AWS Certified Security Specialty SCS-C02 exam, this question tests your ability to distinguish between logs that record OS-level activity versus API-level activity—a common trap is to choose VPC Flow Logs, which only show network traffic patterns, not commands. Remember the memory tip: "OS for commands, CloudTrail for calls" to quickly recall that OS logs capture what happened inside the instance, and CloudTrail captures who authorized the instance to exist.
SCS-C02 Security Logging and Monitoring Practice Question
This SCS-C02 practice question tests your understanding of security logging and monitoring. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 security engineer is investigating a potential security incident involving an EC2 instance that was used to launch an outbound DDoS attack. The engineer needs to determine the source of the attack and the commands executed on the instance. Which logs should be analyzed?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
EC2 instance OS logs (e.g., /var/log/secure) and CloudTrail logs for API calls that launched the instance
Option A is correct because EC2 instance logs (OS logs) capture commands executed on the instance. Option B is wrong because VPC Flow Logs only show network traffic, not commands. Option C is wrong because CloudTrail logs API calls, not OS commands. Option D is wrong because S3 access logs track S3 access, not EC2 activity.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
VPC Flow Logs and Network ACL logs
Why it's wrong here
VPC Flow Logs show network traffic but not commands; Network ACL logs do not exist.
✓
EC2 instance OS logs (e.g., /var/log/secure) and CloudTrail logs for API calls that launched the instance
Why this is correct
OS logs show commands executed; CloudTrail shows who launched the instance.
Related concept
Standard ACLs match source addresses.
✗
S3 server access logs and CloudWatch Logs
Why it's wrong here
S3 logs are irrelevant; CloudWatch Logs may contain OS logs but not by default.
✗
AWS CloudTrail and AWS Config history
Why it's wrong here
CloudTrail shows API calls but not commands; Config shows configuration changes.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Trap categories for this question
Command / output trap
VPC Flow Logs show network traffic but not commands; Network ACL logs do not exist.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related SCS-C02 ACL questions on filtering logic and placement.
Security Logging and Monitoring — This question tests Security Logging and Monitoring — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: EC2 instance OS logs (e.g., /var/log/secure) and CloudTrail logs for API calls that launched the instance — Option A is correct because EC2 instance logs (OS logs) capture commands executed on the instance. Option B is wrong because VPC Flow Logs only show network traffic, not commands. Option C is wrong because CloudTrail logs API calls, not OS commands. Option D is wrong because S3 access logs track S3 access, not EC2 activity.
What should I do if I get this SCS-C02 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related SCS-C02 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Question Discussion
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