- A
Add a bucket policy in Account A that allows the Account B role to perform s3:GetObject on the required prefix.
Cross-account S3 access requires a resource-based permission on the bucket. The bucket policy must explicitly allow the external role to read the needed prefix, otherwise the bucket owner blocks the request even if the role's identity policy allows it.
- B
Add the Account B role to the KMS key policy in Account A with permission to use kms:Decrypt.
Because the objects use SSE-KMS, S3 must be able to decrypt them with the customer managed key. The external role needs authorization in the KMS key policy, or the decrypt step fails even when S3 access is allowed.
- C
Attach an IAM policy in Account B that grants s3:* on the bucket and its objects.
Why wrong: An identity policy in Account B alone cannot authorize access to a bucket in another account. S3 also requires a matching resource policy or equivalent cross-account trust, and broad s3:* is unnecessary for least privilege.
- D
Create an S3 gateway endpoint in Account B so the application can reach the bucket privately.
Why wrong: A gateway endpoint can improve private connectivity, but it does not solve missing authorization. The AccessDenied error here is caused by cross-account permission and KMS policy gaps, not by the network path.
- E
Add an SCP in Account A that allows the Account B role to bypass KMS encryption checks.
Why wrong: Service control policies do not grant access to a specific external role and cannot bypass KMS authorization. SCPs only set guardrails for accounts and OUs; they do not replace bucket or key policies.
Quick Answer
The answer is that you must add a bucket policy in Account A granting s3:GetObject to the Account B role, and add that same role to the KMS key policy in Account A with kms:Decrypt permission. This is required because cross-account S3 KMS encrypted bucket access demands two separate authorization layers: the S3 bucket policy controls access to the object itself, while the KMS key policy controls decryption of the customer managed key. Even if the application role in Account B has an identity policy allowing the read, Account A’s bucket is private by default, and the KMS key policy does not automatically trust external principals. On the SAA-C03 exam, this scenario tests your understanding of cross-account resource-based policies versus identity-based policies, and the common trap is forgetting that KMS encryption adds a second permission boundary. A useful memory tip is “bucket policy for the object, key policy for the lock”—both must explicitly name the foreign role.
SAA-C03 Design Secure Architectures Practice Question
This SAA-C03 practice question tests your understanding of design secure architectures. 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 reporting application in Account B must read files from an S3 bucket in Account A. The bucket contains objects encrypted with a customer managed KMS key in Account A. The application role in Account B already has an identity policy allowing s3:GetObject on the bucket prefix, but requests still fail with AccessDenied. Which two changes are required for the application to read the objects? Select two.
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
Add a bucket policy in Account A that allows the Account B role to perform s3:GetObject on the required prefix.
Option A is correct because cross-account S3 access requires the destination account (Account A) to explicitly grant access via a bucket policy that allows the source account's role (Account B) to perform s3:GetObject on the specified prefix. Without this bucket policy, the S3 service in Account A will deny the request, even if the IAM identity policy in Account B permits the action. Option B is correct because the objects are encrypted with a customer managed KMS key in Account A; the application role in Account B must be added to the KMS key policy with kms:Decrypt permission to decrypt the objects during retrieval. Both the S3 bucket policy and the KMS key policy are required for cross-account encrypted access.
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.
- ✓
Add a bucket policy in Account A that allows the Account B role to perform s3:GetObject on the required prefix.
Why this is correct
Cross-account S3 access requires a resource-based permission on the bucket. The bucket policy must explicitly allow the external role to read the needed prefix, otherwise the bucket owner blocks the request even if the role's identity policy allows it.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Add the Account B role to the KMS key policy in Account A with permission to use kms:Decrypt.
Why this is correct
Because the objects use SSE-KMS, S3 must be able to decrypt them with the customer managed key. The external role needs authorization in the KMS key policy, or the decrypt step fails even when S3 access is allowed.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Attach an IAM policy in Account B that grants s3:* on the bucket and its objects.
Why it's wrong here
An identity policy in Account B alone cannot authorize access to a bucket in another account. S3 also requires a matching resource policy or equivalent cross-account trust, and broad s3:* is unnecessary for least privilege.
- ✗
Create an S3 gateway endpoint in Account B so the application can reach the bucket privately.
Why it's wrong here
A gateway endpoint can improve private connectivity, but it does not solve missing authorization. The AccessDenied error here is caused by cross-account permission and KMS policy gaps, not by the network path.
- ✗
Add an SCP in Account A that allows the Account B role to bypass KMS encryption checks.
Why it's wrong here
Service control policies do not grant access to a specific external role and cannot bypass KMS authorization. SCPs only set guardrails for accounts and OUs; they do not replace bucket or key policies.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume a cross-account IAM role with s3:GetObject permission is sufficient, overlooking that S3 bucket policies and KMS key policies are separate authorization layers that must explicitly allow the external principal, especially when objects are encrypted with a customer managed KMS key.
Detailed technical explanation
How to think about this question
Under the hood, cross-account S3 access with SSE-KMS requires a two-step authorization: the bucket policy must allow the s3:GetObject action for the external principal, and the KMS key policy must allow kms:Decrypt for that same principal. The IAM role in Account B must also have an identity policy allowing both actions, but the bucket and key policies are the gatekeepers in the source account. A real-world scenario is a data lake where Account A stores encrypted data and Account B runs analytics; forgetting the KMS key policy update is a common cause of persistent AccessDenied errors even after the bucket policy is correctly configured.
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
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FAQ
Questions learners often ask
What does this SAA-C03 question test?
Design Secure Architectures — This question tests Design Secure Architectures — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Add a bucket policy in Account A that allows the Account B role to perform s3:GetObject on the required prefix. — Option A is correct because cross-account S3 access requires the destination account (Account A) to explicitly grant access via a bucket policy that allows the source account's role (Account B) to perform s3:GetObject on the specified prefix. Without this bucket policy, the S3 service in Account A will deny the request, even if the IAM identity policy in Account B permits the action. Option B is correct because the objects are encrypted with a customer managed KMS key in Account A; the application role in Account B must be added to the KMS key policy with kms:Decrypt permission to decrypt the objects during retrieval. Both the S3 bucket policy and the KMS key policy are required for cross-account encrypted access.
What should I do if I get this SAA-C03 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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