- A
Stop the EC2 instance and launch a new one in a different subnet.
Why wrong: Stopping the EC2 instance and launching a new one in a different subnet is disruptive and does not address the root cause; the new instance would still be vulnerable to the same attackers if the security group is not updated.
- B
Modify the security group of the EC2 instance to deny inbound SSH from the attacking IPs.
Modifying the security group to deny inbound SSH from the attacking IPs directly blocks the SSH brute force attempts at the instance level. Since the instance uses a security group that can be applied to all instances in the Auto Scaling group, this approach is effective and persistent.
- C
Create a network ACL rule on the subnet to deny inbound traffic from the attacking IPs.
Why wrong: Creating a network ACL rule to deny inbound traffic from the attacking IPs would block traffic at the subnet level, affecting all instances in the subnet. However, network ACLs are stateless and require separate inbound and outbound rules, making them less granular and harder to manage than security groups for this use case.
- D
Configure AWS WAF on the ALB to block the attacking IPs using an IP set rule.
Why wrong: AWS WAF on an ALB only inspects HTTP/HTTPS traffic, not SSH traffic. SSH traffic goes directly to the instance's public IP and does not pass through the ALB. Therefore, WAF cannot block SSH brute force attempts.
SCS-C02 Security Group Practice Question
This SCS-C02 practice question tests your understanding of security logging and monitoring. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: security Group. 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 company uses Amazon GuardDuty to monitor for threats. The security team receives a high-severity finding: 'UnauthorizedAccess:EC2/SSHBruteForce'. The finding indicates a single EC2 instance with a public IP is receiving SSH connection attempts from multiple external IPs. The instance is part of an Auto Scaling group and is fronted by an Application Load Balancer (ALB). The security team wants to block the attacking IPs without disrupting legitimate traffic. What is the MOST effective approach?
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
Modify the security group of the EC2 instance to deny inbound SSH from the attacking IPs.
Option B is correct because modifying the security group of the EC2 instance to deny inbound SSH from the attacking IPs directly blocks the SSH brute force attempts at the instance level. Since the instance is part of an Auto Scaling group, security group modifications will apply to all instances launched with that security group, and updates are immediate. Option D (AWS WAF on ALB) is ineffective because WAF only inspects HTTP/HTTPS traffic at Layer 7, while SSH traffic operates at Layer 4 and does not pass through the ALB; the ALB only handles HTTP/HTTPS, not SSH. The attackers are targeting the instance's public IP directly over SSH, not through the ALB. Therefore, WAF cannot block SSH traffic. Option A (stop instance) is disruptive and unnecessary. Option C (network ACL) would block traffic at the subnet level but would affect all instances in the subnet and is less granular than a security group.
Key principle: Security Group
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Stop the EC2 instance and launch a new one in a different subnet.
Why it's wrong here
Stopping the EC2 instance and launching a new one in a different subnet is disruptive and does not address the root cause; the new instance would still be vulnerable to the same attackers if the security group is not updated.
- ✓
Modify the security group of the EC2 instance to deny inbound SSH from the attacking IPs.
Why this is correct
Modifying the security group to deny inbound SSH from the attacking IPs directly blocks the SSH brute force attempts at the instance level. Since the instance uses a security group that can be applied to all instances in the Auto Scaling group, this approach is effective and persistent.
Related concept
Security Group
- ✗
Create a network ACL rule on the subnet to deny inbound traffic from the attacking IPs.
Why it's wrong here
Creating a network ACL rule to deny inbound traffic from the attacking IPs would block traffic at the subnet level, affecting all instances in the subnet. However, network ACLs are stateless and require separate inbound and outbound rules, making them less granular and harder to manage than security groups for this use case.
- ✗
Configure AWS WAF on the ALB to block the attacking IPs using an IP set rule.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap is that candidates assume AWS WAF can block any type of traffic when attached to an ALB, but WAF only inspects HTTP/HTTPS requests at Layer 7, not SSH traffic at Layer 4. The correct approach is to use a security group to block SSH at the instance level.
Detailed technical explanation
How to think about this question
AWS WAF uses IP set rules to match source IP addresses against a list of IPs to block or allow, and when attached to an ALB, it inspects HTTP/HTTPS requests at the application layer (Layer 7). However, SSH brute force operates at Layer 4 (TCP port 22) and typically does not traverse the ALB; the ALB only forwards HTTP/HTTPS traffic. In this scenario, the SSH brute force attempts are directed at the EC2 instance's public IP, not the ALB's DNS name, so WAF on the ALB would not block SSH traffic. The most effective approach would actually be to use a combination of security group rules to block the attacking IPs at the instance level (if SSH is allowed from specific IPs) or use AWS Network Firewall or a third-party solution to inspect and block SSH traffic at the VPC level. The exam trap is that candidates assume WAF can block all traffic types, but WAF only works for HTTP/HTTPS traffic on an ALB.
KKey Concepts to Remember
- Security Group
- AWS WAF
- Network ACL
- Auto Scaling Group
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Security Group
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review security Group, then practise related SCS-C02 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this SCS-C02 question test?
Security Logging and Monitoring — This question tests Security Logging and Monitoring — Security Group.
What is the correct answer to this question?
The correct answer is: Modify the security group of the EC2 instance to deny inbound SSH from the attacking IPs. — Option B is correct because modifying the security group of the EC2 instance to deny inbound SSH from the attacking IPs directly blocks the SSH brute force attempts at the instance level. Since the instance is part of an Auto Scaling group, security group modifications will apply to all instances launched with that security group, and updates are immediate. Option D (AWS WAF on ALB) is ineffective because WAF only inspects HTTP/HTTPS traffic at Layer 7, while SSH traffic operates at Layer 4 and does not pass through the ALB; the ALB only handles HTTP/HTTPS, not SSH. The attackers are targeting the instance's public IP directly over SSH, not through the ALB. Therefore, WAF cannot block SSH traffic. Option A (stop instance) is disruptive and unnecessary. Option C (network ACL) would block traffic at the subnet level but would affect all instances in the subnet and is less granular than a security group.
What should I do if I get this SCS-C02 question wrong?
Review security Group, then practise related SCS-C02 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Security Group
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Last reviewed: Jul 4, 2026
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