The answer is to revoke the IAM role permissions for the compromised EC2 instance. This is the most effective immediate step because the instance is making unauthorized API calls to S3 using the permissions granted by its attached IAM role; by removing those S3 permissions from the role, you cut off the instance’s ability to access the bucket without terminating or stopping the instance, preserving application availability. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of the principle of least privilege and the difference between network-level controls (like security groups) and identity-based controls—a common trap is confusing network isolation with API access control, since security groups do not block API calls made via the AWS API. Remember: when a compromised EC2 instance is making unauthorized API calls, the fastest containment is to kill the role’s permissions, not the instance. Memory tip: “API calls need IAM, not a security group jam.”
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. 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 healthcare company runs a HIPAA-compliant application on AWS. The application consists of an Application Load Balancer (ALB) in front of a fleet of EC2 instances behind an Auto Scaling group. The EC2 instances store sensitive patient data in an S3 bucket encrypted with SSE-KMS. The security team recently enabled AWS CloudTrail and Amazon GuardDuty. During a routine audit, they notice that an EC2 instance is making repeated API calls to the S3 bucket from an IP address outside the corporate network. The security team suspects the instance is compromised. What is the MOST effective immediate step to contain the potential breach while maintaining availability of the application?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Revoke the IAM role attached to the instance by removing the S3 permissions from the role.
Option C is correct because revoking the instance's IAM role permissions will immediately stop its access to S3 without terminating the instance. Option A is wrong because terminating the instance reduces capacity. Option B is wrong because removing the security group may affect network connectivity but does not stop API calls. Option D is wrong because stopping the instance may disrupt the application but is less granular than revoking permissions.
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.
✓
Revoke the IAM role attached to the instance by removing the S3 permissions from the role.
Why this is correct
This instantly stops the instance's ability to access S3 while keeping the instance running for forensic analysis.
Related concept
Static NAT maps one inside address to one outside address.
✗
Remove the security group that allows outbound traffic from the instance.
Why it's wrong here
This would block all outbound traffic, including legitimate health checks and updates.
✗
Stop the EC2 instance and detach it from the Auto Scaling group.
Why it's wrong here
Stopping the instance removes it from service, but revoking permissions is faster and less disruptive.
✗
Terminate the EC2 instance immediately.
Why it's wrong here
Termination reduces capacity and may cause application disruption; revocation of permissions is more targeted.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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.
Infrastructure Security — This question tests Infrastructure Security — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Revoke the IAM role attached to the instance by removing the S3 permissions from the role. — Option C is correct because revoking the instance's IAM role permissions will immediately stop its access to S3 without terminating the instance. Option A is wrong because terminating the instance reduces capacity. Option B is wrong because removing the security group may affect network connectivity but does not stop API calls. Option D is wrong because stopping the instance may disrupt the application but is less granular than revoking permissions.
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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