SAA-C03 Design Secure Architectures Practice Question
A security analyst needs to let an external vendor (AWS account 555566667777) read data from a set of internal resources in your AWS account. You created an IAM role called VendorReadRole with a policy that allows the required API calls. However, when the vendor tries to access, CloudTrail shows the call fails at AssumeRole with: "Not authorized to perform: sts:AssumeRole".
What is the most appropriate fix?
⚠ Common exam trap
Many candidates confuse the role's permissions policy (which defines what the role can do after being assumed) with the trust policy (which defines who can assume the role), and mistakenly think attaching permissions to the external user or modifying the permissions policy will fix the AssumeRole authorization failure.
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 an allow statement for the vendor in the role’s trust policy to permit sts:AssumeRole from the vendor account (and include any required ExternalId condition).
The error 'Not authorized to perform: sts:AssumeRole' indicates that the role's trust policy does not grant the external AWS account (555566667777) permission to assume the role. The trust policy must include an Allow statement with the sts:AssumeRole action, specifying the external account as the principal, and optionally an ExternalId condition to prevent the confused deputy problem. This is the required configuration for cross-account IAM role access.
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 an allow statement for the vendor in the role’s trust policy to permit sts:AssumeRole from the vendor account (and include any required ExternalId condition).
Why this is correct
AssumeRole is blocked unless the role trust policy allows the vendor principal. The role’s permissions policy alone cannot permit assumption.
- ✗
Attach the same allow policy to the vendor account’s existing IAM user so the user can call sts:AssumeRole directly into your role.
Why it's wrong here
Even if the vendor user can call sts:AssumeRole, your role still must trust that principal. Without trust, the AssumeRole request is denied.
- ✗
Replace the AssumeRole call with GetCallerIdentity so the vendor can infer permissions without assuming the role.
Why it's wrong here
GetCallerIdentity does not grant access to the internal resources. The vendor still needs a trusted identity and proper permissions.
- ✗
Enable MFA on the vendor’s IAM user and require MFA for your role using condition keys in the permissions policy.
Why it's wrong here
MFA requirements affect the authorization flow but do not solve the root cause. The trust policy must first allow the vendor to assume the role.
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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.