- A
Create IAM user access keys in account A and attach the UploadRole policy directly to those keys.
Why wrong: Using static access keys increases risk and bypasses role-based trust controls. It also does not leverage the existing role in account B. Attaching account B permissions directly to account A identities is typically not least-privilege for cross-account access.
- B
Update the trust policy on UploadRole (account B) to allow sts:AssumeRole from the app’s IAM role or principal in account A.
A cross-account role requires both an IAM permissions policy and a trust policy. The trust policy must allow the specific principal in account A to call sts:AssumeRole into account B’s role. With that trust in place, the app can obtain temporary credentials and then use the UploadRole permissions for s3:PutObject.
- C
Add s3:PutObject permissions to the bucket policy in account B for all principals in account A.
Why wrong: Bucket policies can grant access, but granting broadly to account A principals is harder to keep least-privileged. It also does not address that sts:AssumeRole must be authorized for the app to use the intended role. This option ignores the missing trust relationship root cause.
- D
Attach an SCP (service control policy) in AWS Organizations to deny sts:AssumeRole unless the caller uses an MFA device.
Why wrong: An SCP can restrict actions at the organization level, but it won’t fix the current AccessDenied stemming from missing trust. If MFA enforcement is needed, it should be reflected in an appropriate condition in the trust policy, not as the primary missing permission.
SAA-C03 Design Secure Architectures Practice Question
This SAA-C03 practice question tests your understanding of design secure architectures. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: cross-account access via IAM roles requires a trust policy.. 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.
Company A runs an internal app in account A. The app needs to upload objects to an S3 bucket in account B. When the app calls S3, it receives AccessDenied for s3:PutObject. The team already created an IAM role in account B named UploadRole with a policy allowing s3:PutObject. They did not yet set up any trust relationship. Which change most directly fixes the access problem with least privilege?
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 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
Update the trust policy on UploadRole (account B) to allow sts:AssumeRole from the app’s IAM role or principal in account A.
The app in account A needs to assume the UploadRole in account B to gain s3:PutObject permissions. Without a trust policy on UploadRole that allows sts:AssumeRole from the app's IAM principal in account A, the role cannot be assumed, and the S3 PutObject call fails with AccessDenied. Updating the trust policy is the most direct fix and follows least privilege by granting only the necessary cross-account role assumption.
Key principle: Cross-account access via IAM roles requires a trust policy.
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 IAM user access keys in account A and attach the UploadRole policy directly to those keys.
Why it's wrong here
Using static access keys increases risk and bypasses role-based trust controls. It also does not leverage the existing role in account B. Attaching account B permissions directly to account A identities is typically not least-privilege for cross-account access.
- ✓
Update the trust policy on UploadRole (account B) to allow sts:AssumeRole from the app’s IAM role or principal in account A.
Why this is correct
A cross-account role requires both an IAM permissions policy and a trust policy. The trust policy must allow the specific principal in account A to call sts:AssumeRole into account B’s role. With that trust in place, the app can obtain temporary credentials and then use the UploadRole permissions for s3:PutObject.
Clue confirmation
The clue word "least" in the question point toward this answer.
Related concept
Cross-account access via IAM roles requires a trust policy.
- ✗
Add s3:PutObject permissions to the bucket policy in account B for all principals in account A.
Why it's wrong here
Bucket policies can grant access, but granting broadly to account A principals is harder to keep least-privileged. It also does not address that sts:AssumeRole must be authorized for the app to use the intended role. This option ignores the missing trust relationship root cause.
- ✗
Attach an SCP (service control policy) in AWS Organizations to deny sts:AssumeRole unless the caller uses an MFA device.
Why it's wrong here
An SCP can restrict actions at the organization level, but it won’t fix the current AccessDenied stemming from missing trust. If MFA enforcement is needed, it should be reflected in an appropriate condition in the trust policy, not as the primary missing permission.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often think bucket policies alone can grant cross-account access without considering the need for role assumption and trust policies, leading them to choose Option C as a simpler but overly permissive solution.
Detailed technical explanation
How to think about this question
Under the hood, cross-account S3 access via IAM roles uses AWS Security Token Service (STS) to issue temporary credentials; the trust policy on the role in account B must explicitly list the IAM principal (user or role) from account A as a trusted entity. A common subtlety is that the app's IAM role in account A also needs an IAM policy allowing sts:AssumeRole on the UploadRole ARN, otherwise the assumption call itself fails. In real-world scenarios, forgetting to add both the trust policy and the permission policy on the caller side is a frequent cause of AccessDenied errors.
KKey Concepts to Remember
- Cross-account access via IAM roles requires a trust policy.
- A trust policy specifies which principals can assume the role.
- The `sts:AssumeRole` action is required for cross-account role assumption.
- Trust policies are resource-based policies attached to IAM roles.
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
Cross-account access via IAM roles requires a trust policy.
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 — Cross-account access via IAM roles requires a trust policy..
What is the correct answer to this question?
The correct answer is: Update the trust policy on UploadRole (account B) to allow sts:AssumeRole from the app’s IAM role or principal in account A. — The app in account A needs to assume the UploadRole in account B to gain s3:PutObject permissions. Without a trust policy on UploadRole that allows sts:AssumeRole from the app's IAM principal in account A, the role cannot be assumed, and the S3 PutObject call fails with AccessDenied. Updating the trust policy is the most direct fix and follows least privilege by granting only the necessary cross-account role assumption.
What should I do if I get this SAA-C03 question wrong?
Review cross-account access via IAM roles requires a trust policy., then practise related SAA-C03 questions on the same topic to reinforce the concept.
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?
Cross-account access via IAM roles requires a trust policy.
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Last reviewed: Jun 11, 2026
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