- A
A bucket ACL in Account A granting READ access to Account B
Why wrong: ACLs are legacy and do not integrate with IAM policies effectively for cross-account.
- B
A bucket policy in Account A granting s3:GetObject to Account B and an IAM policy in Account B allowing s3:GetObject
Both policies are needed: the bucket policy allows cross-account access, and the IAM policy allows the user to perform the action.
- C
An IAM policy in Account A that allows s3:GetObject
Why wrong: The bucket policy is needed in Account A; the IAM policy is needed in Account B.
- D
An IAM role in Account B that grants s3:GetObject to Account A
Why wrong: The IAM role should be in Account A for cross-account access.
Question 772 of 1,748
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. 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 company wants to allow cross-account access to an S3 bucket. The bucket owner (Account A) wants to grant read-only access to users in Account B. Which combination of policies is required?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A bucket policy in Account A granting s3:GetObject to Account B and an IAM policy in Account B allowing s3:GetObject
Option B is correct because cross-account access to S3 requires a resource-based policy (bucket policy) in the account that owns the bucket (Account A) granting the desired permissions to the principal in Account B, and an identity-based policy (IAM policy) in the accessing account (Account B) that allows the user or role to perform the action (s3:GetObject). Option A is incorrect because bucket ACLs are legacy and do not provide the same level of control; they cannot grant access to accounts in a way that works with IAM policies alone. Option C is incorrect because an IAM policy in Account A would only grant permissions to entities within Account A, not to users in Account B. Option D is incorrect because an IAM role in Account B would allow Account A to access Account B's resources, not the reverse; the role would need to be in Account A to be assumed by Account B users.
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.
- ✗
A bucket ACL in Account A granting READ access to Account B
Why it's wrong here
ACLs are legacy and do not integrate with IAM policies effectively for cross-account.
- ✓
A bucket policy in Account A granting s3:GetObject to Account B and an IAM policy in Account B allowing s3:GetObject
Why this is correct
Both policies are needed: the bucket policy allows cross-account access, and the IAM policy allows the user to perform the action.
Related concept
Standard ACLs match source addresses.
- ✗
An IAM policy in Account A that allows s3:GetObject
Why it's wrong here
The bucket policy is needed in Account A; the IAM policy is needed in Account B.
- ✗
An IAM role in Account B that grants s3:GetObject to Account A
Why it's wrong here
The IAM role should be in Account A for cross-account access.
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.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
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.
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FAQ
Questions learners often ask
What does this SCS-C02 question test?
Infrastructure Security — This question tests Infrastructure Security — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: A bucket policy in Account A granting s3:GetObject to Account B and an IAM policy in Account B allowing s3:GetObject — Option B is correct because cross-account access to S3 requires a resource-based policy (bucket policy) in the account that owns the bucket (Account A) granting the desired permissions to the principal in Account B, and an identity-based policy (IAM policy) in the accessing account (Account B) that allows the user or role to perform the action (s3:GetObject). Option A is incorrect because bucket ACLs are legacy and do not provide the same level of control; they cannot grant access to accounts in a way that works with IAM policies alone. Option C is incorrect because an IAM policy in Account A would only grant permissions to entities within Account A, not to users in Account B. Option D is incorrect because an IAM role in Account B would allow Account A to access Account B's resources, not the reverse; the role would need to be in Account A to be assumed by Account B users.
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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Last reviewed: Jun 20, 2026
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