The answer is to use S3 VPC Endpoints with a bucket policy that only allows access from the VPC endpoint, combined with Systems Manager Session Manager instead of SSH. This works because the VPC endpoint forces all S3 traffic to stay within the AWS network, so even if an attacker compromises an EC2 instance and steals its IAM credentials, they cannot exfiltrate data over the public internet—the bucket policy explicitly denies any access that doesn’t originate from the endpoint. Meanwhile, Session Manager eliminates inbound SSH ports entirely, reducing the attack surface and ensuring that all administrative access is controlled through IAM, not keys or bastion hosts. On the SCS-C02 exam, this scenario tests your understanding of limiting blast radius through network segmentation and identity-based controls, not just detection tools like GuardDuty. A common trap is to focus on patching or least privilege alone, but the real key is preventing outbound data movement. Memory tip: “Endpoint for egress, Session for access.”
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 financial services company runs a critical application on Amazon EC2 instances in a VPC. The application processes sensitive financial data and must meet strict compliance requirements. The security team recently discovered that an EC2 instance was compromised due to an unpatched vulnerability. The attacker used the instance's IAM role to access an S3 bucket containing customer data and exfiltrated the data. The security team needs to prevent such incidents in the future. They have implemented the following controls:
- All EC2 instances are launched in private subnets.
- The IAM roles used by EC2 instances follow the principle of least privilege.
- Security groups restrict inbound and outbound traffic.
- AWS Systems Manager Patch Manager is used to patch instances.
- AWS CloudTrail is enabled and logs are sent to a centralized S3 bucket.
- Amazon GuardDuty is enabled.
Despite these controls, the team is concerned about the blast radius if an instance is compromised again. Which additional measure would MOST effectively limit the blast radius of a compromised EC2 instance?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "least"
Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use S3 VPC Endpoints with a bucket policy that only allows access from the VPC endpoint, and use Systems Manager Session Manager instead of SSH.
Option B is correct because using an S3 VPC endpoint with a bucket policy that restricts access exclusively to that endpoint ensures that compromised EC2 instances can only reach S3 through the VPC endpoint, preventing data exfiltration over the internet. Additionally, replacing SSH with Systems Manager Session Manager eliminates the need for open inbound SSH ports and provides fine-grained access control through IAM, reducing the attack surface and blast radius.
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.
✗
Enable VPC Flow Logs to monitor traffic to S3.
Why it's wrong here
Flow logs are detective and do not prevent data exfiltration.
✓
Use S3 VPC Endpoints with a bucket policy that only allows access from the VPC endpoint, and use Systems Manager Session Manager instead of SSH.
Why this is correct
This restricts S3 access to the VPC and reduces the attack surface for data exfiltration.
Clue confirmation
The clue word "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Deploy AWS WAF in front of the S3 bucket.
Why it's wrong here
AWS WAF is for web ACLs, not for restricting access from EC2.
✗
Create an AWS Config rule to detect S3 access from EC2 instances.
Why it's wrong here
Config rules are detective, not preventive.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may choose VPC Flow Logs (Option A) thinking it provides active protection, but it is only a monitoring tool that does not reduce the blast radius; the key is to implement network-level and access-level restrictions that prevent data exfiltration even if an instance is compromised.
Detailed technical explanation
How to think about this question
S3 VPC endpoints use AWS PrivateLink to route S3 traffic through the AWS network without traversing the internet, and when combined with a bucket policy that includes a condition like 'aws:SourceVpce', only traffic originating from that specific VPC endpoint is allowed. Systems Manager Session Manager establishes a secure, auditable shell session without opening inbound ports or managing SSH keys, and it can be further restricted using IAM policies to control which instances and commands are accessible. This layered approach ensures that even if an instance is compromised, the attacker cannot use its IAM role to exfiltrate data over the internet or pivot via SSH.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Infrastructure Security — This question tests Infrastructure Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use S3 VPC Endpoints with a bucket policy that only allows access from the VPC endpoint, and use Systems Manager Session Manager instead of SSH. — Option B is correct because using an S3 VPC endpoint with a bucket policy that restricts access exclusively to that endpoint ensures that compromised EC2 instances can only reach S3 through the VPC endpoint, preventing data exfiltration over the internet. Additionally, replacing SSH with Systems Manager Session Manager eliminates the need for open inbound SSH ports and provides fine-grained access control through IAM, reducing the attack surface and blast radius.
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.
Are there clue words in this question I should notice?
Yes — watch for: "least". You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
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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