The answer is to create a snapshot of the EBS volumes and apply a restrictive security group that blocks all outbound traffic. This combination is correct because the snapshot preserves the forensic data on disk for later analysis, while the security group immediately stops the DDoS traffic at the network level without terminating the instance, which would destroy volatile memory evidence. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of incident response procedures, specifically the difference between network isolation via security groups and data preservation via snapshots. A common trap is to choose terminating the instance or detaching the volume, but both destroy critical forensic data or the running state. Remember the mnemonic “Snap and Block”: snapshot the disk, block the traffic.
SCS-C02 Threat Detection and Incident Response Practice Question
This SCS-C02 practice question tests your understanding of threat detection and incident response. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 team suspects that an attacker has compromised an EC2 instance and is using it to launch outbound DDoS attacks. The team needs to quickly isolate the instance while preserving forensic data. Which combination of actions should the team take? (Choose TWO.)
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 that blocks all outbound traffic.
Option A is correct because applying a restrictive security group that blocks all outbound traffic immediately stops the EC2 instance from sending any network packets, including DDoS traffic, without terminating the instance. This preserves the running state and allows forensic data collection from the instance's memory and disk. Security groups act as a stateful virtual firewall at the instance level, so blocking outbound traffic effectively isolates the instance from the network.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Apply a restrictive security group that blocks all outbound traffic.
Why this is correct
This isolates the instance by preventing outbound connections while allowing forensic access via inbound rules if needed.
Related concept
Read the scenario before looking for a memorised answer.
✗
Modify the network ACL for the subnet to deny all outbound traffic.
Why it's wrong here
NACL changes affect all instances in the subnet, not just the compromised one.
✓
Create a snapshot of the EBS volumes attached to the EC2 instance.
Why this is correct
Snapshots preserve the current state of the volumes for forensic analysis.
Related concept
Read the scenario before looking for a memorised answer.
✗
Detach the instance from the Auto Scaling group.
Why it's wrong here
Detaching does not block network traffic; the instance remains accessible.
✗
Terminate the EC2 instance immediately.
Why it's wrong here
Termination destroys evidence and prevents further investigation.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse network ACLs with security groups, thinking a subnet-level NACL change is equivalent to instance-level isolation, but NACLs affect all instances in the subnet and are stateless, making them unsuitable for targeted incident response.
Detailed technical explanation
How to think about this question
Security groups are stateful and evaluate outbound rules independently; blocking all outbound traffic at the security group level ensures that even if the instance is compromised with root-level access, it cannot bypass the hypervisor-enforced firewall. In contrast, network ACLs are stateless and require explicit rules for both inbound and outbound traffic, making them less granular for instance-level isolation. For forensic preservation, creating an EBS snapshot (Option C) captures the volume's data at a point in time, including deleted files that may still be recoverable, while the instance remains running for memory acquisition via tools like LiME or F-Response.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Threat Detection and Incident Response — This question tests Threat Detection and Incident Response — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Apply a restrictive security group that blocks all outbound traffic. — Option A is correct because applying a restrictive security group that blocks all outbound traffic immediately stops the EC2 instance from sending any network packets, including DDoS traffic, without terminating the instance. This preserves the running state and allows forensic data collection from the instance's memory and disk. Security groups act as a stateful virtual firewall at the instance level, so blocking outbound traffic effectively isolates the instance from the network.
What should I do if I get this SCS-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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