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Question 357 of 1,040

Design Secure Architectures →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is to update the trust policy on the UploadRole in account B to allow sts:AssumeRole from the app’s IAM principal in account A. This is correct because cross-account access requires two distinct IAM components: a permissions policy granting the desired actions (like s3:PutObject) and a trust policy explicitly authorizing the external principal to assume the role. Without the trust relationship, the role exists but is locked to its own account, so any sts:AssumeRole call from account A is denied by default. On the SAA-C03 exam, this scenario tests your understanding that a trust policy is the gatekeeper for cross-account role assumption—a common trap is thinking the permissions policy alone suffices. Remember the two-policy rule: permissions say *what* you can do, trust says *who* can do it. Memory tip: “Trust first, then permissions—no trust, no access.”

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. 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.

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.

Question 1mediummultiple choice

Full question →

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.

Full breakdown with real-world context →

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, resulting in AccessDenied. Updating the trust policy directly establishes the cross-account trust relationship with least privilege, as it grants only the necessary assume-role capability.

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 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
Read the scenario before looking for a memorised answer.
✗
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 solve cross-account access, but without a trust policy on the IAM role, the app cannot assume the role to obtain the required permissions.

Detailed technical explanation

How to think about this question

Cross-account access via IAM roles relies on the AWS Security Token Service (STS) to issue temporary credentials. The trust policy on the role in account B must explicitly allow the sts:AssumeRole action from the app's IAM role or user ARN in account A, and the app must call sts:AssumeRole to receive temporary credentials. Without this trust policy, the role is invisible to account A, and any direct S3 PutObject call will fail because the app lacks the necessary permissions in account B.

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.

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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: 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, resulting in AccessDenied. Updating the trust policy directly establishes the cross-account trust relationship with least privilege, as it grants only the necessary assume-role capability.

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.

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?

Read the scenario before looking for a memorised answer.

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Same concept, more angles

1 more ways this is tested on SAA-C03

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. 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?

medium

A.Create IAM user access keys in account A and attach the UploadRole policy directly to those keys.
✓ B.Update the trust policy on UploadRole (account B) to allow sts:AssumeRole from the app’s IAM role or principal in account A.
C.Add s3:PutObject permissions to the bucket policy in account B for all principals in account A.
D.Attach an SCP (service control policy) in AWS Organizations to deny sts:AssumeRole unless the caller uses an MFA device.

Why B: 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.

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