The correct answer is to create an IAM role in Account B, trust Account A's AppRole to assume it with STS, and then access the bucket using temporary credentials. This approach eliminates long-lived keys by leveraging AWS Security Token Service (STS) to issue temporary, scoped credentials that the workload in Account A uses to authenticate to the S3 bucket in Account B. On the SAA-C03 exam, this scenario tests your understanding of cross-account access patterns and the principle of least privilege, often appearing as a scenario where a candidate mistakenly proposes sharing access keys or bucket policies with a principal in another account. A common trap is thinking a bucket policy alone suffices for cross-account access without an IAM role, but the role-based STS flow is required to avoid permanent keys. Memory tip: "Trust then Assume" — the trusting account (B) creates the role, and the trusted account (A) assumes it via STS for temporary access.
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.
Exhibit
Cross-account access attempt:
Account A:
- EC2 instance profile role: arn:aws:iam::111122223333:role/AppRole
- Identity policy allows s3:GetObject on arn:aws:s3:::shared-data-bucket/*
Account B:
- Bucket policy currently allows the account root principal only
- Application log shows: AccessDenied when calling GetObject on shared-data-bucket
- Security requirement: no static credentials; access must be revocable centrally
Based on the exhibit, what is the most appropriate fix so the workload in Account A can access the S3 bucket in Account B without using long-lived access keys?
Cross-account access attempt:
Account A:
- EC2 instance profile role: arn:aws:iam::111122223333:role/AppRole
- Identity policy allows s3:GetObject on arn:aws:s3:::shared-data-bucket/*
Account B:
- Bucket policy currently allows the account root principal only
- Application log shows: AccessDenied when calling GetObject on shared-data-bucket
- Security requirement: no static credentials; access must be revocable centrally
A
Create an IAM role in Account B, trust Account A's AppRole to assume it with STS, and then access the bucket using temporary credentials.
Assuming a role in the target account is a clean cross-account pattern that uses temporary credentials instead of static keys. The trust policy in Account B controls who may assume the role, and the role in B can then be given the exact S3 permissions needed. This is easy to revoke centrally by changing the trust relationship or role policy.
B
Attach AmazonS3FullAccess to the instance profile role in Account A and keep using the same direct access path.
Why wrong: This broadens permissions in the source account but does not solve the cross-account trust and resource authorization model cleanly.
C
Add an SCP to Account A that allows S3 actions against buckets in Account B.
Why wrong: SCPs restrict permissions within AWS Organizations but do not grant cross-account access to a bucket.
D
Enable S3 versioning on the bucket so cross-account requests are automatically trusted.
Why wrong: Versioning is useful for recovery, but it has nothing to do with authorization between accounts.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create an IAM role in Account B, trust Account A's AppRole to assume it with STS, and then access the bucket using temporary credentials.
Option A is correct because it uses AWS Security Token Service (STS) to allow the workload in Account A to assume an IAM role in Account B, obtaining temporary credentials that grant access to the S3 bucket. This eliminates the need for long-lived access keys and follows the principle of least privilege, as the role can be scoped to specific S3 actions and resources.
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.
✓
Create an IAM role in Account B, trust Account A's AppRole to assume it with STS, and then access the bucket using temporary credentials.
Why this is correct
Assuming a role in the target account is a clean cross-account pattern that uses temporary credentials instead of static keys. The trust policy in Account B controls who may assume the role, and the role in B can then be given the exact S3 permissions needed. This is easy to revoke centrally by changing the trust relationship or role policy.
Related concept
Read the scenario before looking for a memorised answer.
✗
Attach AmazonS3FullAccess to the instance profile role in Account A and keep using the same direct access path.
Why it's wrong here
This broadens permissions in the source account but does not solve the cross-account trust and resource authorization model cleanly.
✗
Add an SCP to Account A that allows S3 actions against buckets in Account B.
Why it's wrong here
SCPs restrict permissions within AWS Organizations but do not grant cross-account access to a bucket.
✗
Enable S3 versioning on the bucket so cross-account requests are automatically trusted.
Why it's wrong here
Versioning is useful for recovery, but it has nothing to do with authorization between accounts.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse SCPs with resource-based policies or assume that attaching a managed policy to an instance profile automatically grants cross-account access, overlooking the need for explicit trust and bucket policies in the target account.
Detailed technical explanation
How to think about this question
When the workload in Account A assumes the IAM role in Account B via STS, it receives temporary security credentials consisting of an access key ID, secret access key, and session token, which are valid for a configurable duration (default 1 hour, max 12 hours for roles). The role's trust policy must specify the IAM user or role in Account A as a trusted entity, and the S3 bucket policy in Account B must grant the role permissions (e.g., s3:GetObject) to the bucket. This pattern is commonly used in multi-account architectures where central logging or data lakes are hosted in a shared services account.
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.
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: Create an IAM role in Account B, trust Account A's AppRole to assume it with STS, and then access the bucket using temporary credentials. — Option A is correct because it uses AWS Security Token Service (STS) to allow the workload in Account A to assume an IAM role in Account B, obtaining temporary credentials that grant access to the S3 bucket. This eliminates the need for long-lived access keys and follows the principle of least privilege, as the role can be scoped to specific S3 actions and resources.
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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Question Discussion
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