SAA-C03 Design Secure Architectures Practice Question
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?
⚠ Common exam trap
Watch out — 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.
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.
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.
- ✗
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.
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 |
Go deeper
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SAA-C03 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SAA-C03 exam.