- A
Enable multi-factor authentication for all users
Why wrong: MFA helps but is not an immediate response to an active attack.
- B
Block the source IP address in the security group
Blocking the source IP stops the attack without disrupting legitimate traffic.
- C
Remove the instance from the auto-scaling group
Why wrong: This does not address the immediate attack.
- D
Disable the SSH service on the instance
Why wrong: Disabling SSH may affect legitimate access; blocking the attacker is more precise.
Question 55 of 1,000
CS0-003 Security Operations Practice Question
This CS0-003 practice question tests your understanding of security operations. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 SOC analyst is investigating an alert from AWS GuardDuty that indicates 'UnauthorizedAccess:EC2/SSHBruteForce'. The analyst reviews CloudTrail logs and sees multiple failed SSH login attempts from a single IP address. What initial triage action should the analyst take?
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
✓
Block the source IP address in the security group
The best initial action is to block the source IP address at the security group or network ACL to stop the brute force attack, then investigate further.
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.
- ✗
Enable multi-factor authentication for all users
Why it's wrong here
MFA helps but is not an immediate response to an active attack.
- ✓
Block the source IP address in the security group
Why this is correct
Blocking the source IP stops the attack without disrupting legitimate traffic.
Related concept
Standard ACLs match source addresses.
- ✗
Remove the instance from the auto-scaling group
Why it's wrong here
This does not address the immediate attack.
- ✗
Disable the SSH service on the instance
Why it's wrong here
Disabling SSH may affect legitimate access; blocking the attacker is more precise.
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.
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 security analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. 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. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
Visual reference
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 CS0-003 ACL questions on filtering logic and placement.
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FAQ
Questions learners often ask
What does this CS0-003 question test?
Security Operations — This question tests Security Operations — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Block the source IP address in the security group — The best initial action is to block the source IP address at the security group or network ACL to stop the brute force attack, then investigate further.
What should I do if I get this CS0-003 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 CS0-003 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Last reviewed: Jul 4, 2026
This CS0-003 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 CS0-003 exam.
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