The answer is that the Deny statement in the S3 bucket policy overrides the Allow from the IAM role, blocking the EC2 instance’s access. This happens because when an IAM role grants an Allow for s3:GetObject, but the bucket policy includes a Deny with the condition aws:SourceIp matching the instance’s IP range (10.0.0.0/8), the explicit Deny always takes precedence—even over a broader Allow. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of the evaluation logic where bucket policy Deny statements are absolute, regardless of identity-based permissions. A common trap is assuming the IAM role’s Allow is sufficient, but bucket policies act as a separate authorization layer. Remember the key rule: an explicit Deny in any policy (resource or identity) wins over any Allow. For a quick memory tip, think “Deny is the final veto”—once a Deny matches, no Allow can save the request.
SCS-C02 Identity and Access Management Practice Question
This SCS-C02 practice question tests your understanding of identity and access management. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 security engineer is troubleshooting an issue where an EC2 instance cannot access an S3 bucket even though the IAM role attached to the instance has an Allow policy for s3:GetObject. The S3 bucket policy includes a Deny statement with the condition 'aws:SourceIp': ['10.0.0.0/8']. What is the likely cause of the failure?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Deny statement in the bucket policy is blocking the request because the EC2 instance’s IP falls within the 10.0.0.0/8 range.
Option A is correct because the Deny in the bucket policy overrides the Allow from the IAM role. Even though the role allows the action, the bucket policy denies it based on the source IP. Option B is wrong because roles can access S3. Option C is irrelevant. Option D is not the cause.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The IAM role’s permissions boundary is blocking the action.
Why it's wrong here
No permissions boundary mentioned.
✗
The IAM role does not have an STS trust policy.
Why it's wrong here
EC2 instances automatically assume roles without needing STS trust policy.
✗
The S3 bucket is in a different region.
Why it's wrong here
Cross-region access is allowed unless explicitly denied.
✓
The Deny statement in the bucket policy is blocking the request because the EC2 instance’s IP falls within the 10.0.0.0/8 range.
Why this is correct
The bucket policy denies all requests from the private IP range, including the EC2 instance.
Related concept
Standard ACLs match source addresses.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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 ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related SCS-C02 ACL questions on filtering logic and placement.
Identity and Access Management — This question tests Identity and Access Management — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The Deny statement in the bucket policy is blocking the request because the EC2 instance’s IP falls within the 10.0.0.0/8 range. — Option A is correct because the Deny in the bucket policy overrides the Allow from the IAM role. Even though the role allows the action, the bucket policy denies it based on the source IP. Option B is wrong because roles can access S3. Option C is irrelevant. Option D is not the cause.
What should I do if I get this SCS-C02 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related SCS-C02 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Question Discussion
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