The answer is to modify the security group associated with the instance to remove all inbound and outbound rules. This approach is correct because security groups act as a virtual firewall at the instance level, and removing all rules instantly drops all traffic to and from that specific EC2 instance without stopping it, preserving volatile memory for forensic analysis. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of incident response isolation techniques, often presenting traps like detaching the instance (which stops it and loses memory data) or changing network ACLs (which affect the entire subnet, not just the compromised host). A common memory tip is to think of security groups as a surgical scalpel for instance-level isolation, whereas NACLs are a blunt axe for subnet-wide changes. Remember: to isolate a single instance while keeping it alive for forensics, always modify its security group, not the instance state or subnet rules.
SCS-C02 Threat Detection and Incident Response Practice Question
This SCS-C02 practice question tests your understanding of threat detection and incident response. 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 company has an incident response (IR) process that includes isolating compromised EC2 instances. During a security incident, the IR team needs to block all traffic to and from a compromised instance while preserving the instance for forensic analysis. Which approach should the team take?
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 associated with the instance to remove all inbound and outbound rules.
Modifying the security group to deny all traffic is the quickest way to isolate an instance while keeping it running. Detaching the instance stops it and may lose volatile data. Deleting the instance destroys evidence. Changing network ACLs affects the entire subnet, not just the instance.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Detach the instance from the Auto Scaling group and stop it.
Why it's wrong here
Stopping the instance may lose volatile memory evidence.
✓
Modify the security group associated with the instance to remove all inbound and outbound rules.
Why this is correct
This blocks all traffic to/from the instance while keeping it running for forensics.
Update the network ACL for the subnet to deny all traffic.
Why it's wrong here
This affects all instances in the subnet, not just the compromised one.
✗
Terminate the instance immediately.
Why it's wrong here
Terminating the instance destroys forensic evidence.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Threat Detection and Incident Response — This question tests Threat Detection and Incident Response — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Modify the security group associated with the instance to remove all inbound and outbound rules. — Modifying the security group to deny all traffic is the quickest way to isolate an instance while keeping it running. Detaching the instance stops it and may lose volatile data. Deleting the instance destroys evidence. Changing network ACLs affects the entire subnet, not just the instance.
What should I do if I get this SCS-C02 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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