The answer is to create an Amazon EventBridge rule that triggers an AWS Lambda function to remove the instance from the security group. This approach works because GuardDuty sends its findings as events to EventBridge, and a Lambda function subscribed to that event can programmatically modify the security group’s inbound rules to isolate the compromised EC2 instance. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of the GuardDuty-to-EventBridge-to-Lambda pipeline as the standard serverless remediation pattern. A common trap is assuming GuardDuty has native remediation actions—it does not—or thinking AWS Config can react to GuardDuty findings, which it cannot. While Systems Manager Automation is possible, it requires a pre-built runbook and adds unnecessary complexity for a simple security group removal. Memory tip: think of the "GEL" pipeline—GuardDuty sends findings to EventBridge, which triggers Lambda to isolate the instance.
SCS-C02 Security Logging and Monitoring Practice Question
This SCS-C02 practice question tests your understanding of security logging and monitoring. 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 and wants to automatically isolate a compromised EC2 instance by removing it from the security group. Which approach should be used?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create an Amazon EventBridge rule that triggers an AWS Lambda function to remove the instance from the security group.
GuardDuty can send findings to EventBridge, which triggers a Lambda function to modify the security group. Option A is wrong because GuardDuty does not have native remediation actions. Option C is wrong because Systems Manager Automation is possible but requires a runbook. Option D is wrong because AWS Config does not react to GuardDuty findings.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Set up an AWS Config rule to detect the finding and remediate.
Why it's wrong here
AWS Config evaluates resource configurations, not GuardDuty findings.
✗
Configure GuardDuty to directly modify the security group.
Why it's wrong here
GuardDuty does not have the capability to modify resources directly.
✓
Create an Amazon EventBridge rule that triggers an AWS Lambda function to remove the instance from the security group.
Why this is correct
EventBridge can capture GuardDuty findings and invoke Lambda for automated remediation.
Related concept
Static NAT maps one inside address to one outside address.
✗
Use AWS Systems Manager Automation to automatically modify the security group based on GuardDuty findings.
Why it's wrong here
This is possible but requires custom configuration; EventBridge with Lambda is simpler.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SCS-C02 NAT questions on configuration and troubleshooting.
Security Logging and Monitoring — This question tests Security Logging and Monitoring — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Create an Amazon EventBridge rule that triggers an AWS Lambda function to remove the instance from the security group. — GuardDuty can send findings to EventBridge, which triggers a Lambda function to modify the security group. Option A is wrong because GuardDuty does not have native remediation actions. Option C is wrong because Systems Manager Automation is possible but requires a runbook. Option D is wrong because AWS Config does not react to GuardDuty findings.
What should I do if I get this SCS-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SCS-C02 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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