The correct actions are to restrict the security group to known IPs, move the instance to a private subnet with a NAT gateway, and use AWS Systems Manager Session Manager instead of SSH. These three steps directly remediate a GuardDuty port probe unprotected port finding by eliminating the public attack surface: the security group change blocks unauthorized inbound traffic, the private subnet removes the public IP exposure, and Session Manager replaces SSH with a secure, keyless access method that operates through the AWS API. On the AWS Certified Security Specialty SCS-C02 exam, this question tests your ability to apply layered defense for EC2 instances, not just suppress alerts—a common trap is choosing GuardDuty suppression, which only hides the finding without fixing the vulnerability. Remember the three-layer mnemonic: Lock, Hide, Replace—lock the security group, hide the instance in a private subnet, and replace SSH with Session Manager.
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 uses Amazon GuardDuty to monitor its AWS environment. The security team has received a GuardDuty finding of type 'Recon:EC2/PortProbeUnprotectedPort'. The finding indicates that an EC2 instance has an open SSH port that is being probed from the internet. The team wants to reduce the attack surface and prevent future probes. Which THREE actions should the team take? (Choose THREE.)
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 to allow SSH only from specific IP addresses.
Options A, C, and D are correct: changing the security group to restrict SSH access to known IPs, placing the instance in a private subnet with a NATgateway, and using Systems Manager Session Manager instead of SSH. Option B is wrong because terminating the instance is not necessary if it can be secured. Option E is wrong because GuardDuty suppression is for false positives, not for fixing actual vulnerabilities.
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.
✗
Suppress the GuardDuty finding to reduce noise.
Why it's wrong here
Suppression does not fix the underlying issue; it only hides the finding.
✓
Modify the security group to allow SSH only from specific IP addresses.
Why this is correct
Restricting SSH access reduces the attack surface.
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 to allow SSH only from specific IP addresses. — Options A, C, and D are correct: changing the security group to restrict SSH access to known IPs, placing the instance in a private subnet with a NAT gateway, and using Systems Manager Session Manager instead of SSH. Option B is wrong because terminating the instance is not necessary if it can be secured. Option E is wrong because GuardDuty suppression is for false positives, not for fixing actual vulnerabilities.
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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