Quick Answer
The answer is that the developer is not providing the required external ID when calling sts:AssumeRole. A cross-account role trust policy can include a condition that mandates an external ID, often used to prevent the confused deputy problem by requiring a unique identifier from the trusting account. Even if the trust policy allows the dev account and the developer’s IAM policy permits sts:AssumeRole, the call will fail if the external ID is missing from the CLI command or SDK request. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of how external IDs enforce a three-way trust—between the trusting account, the trusted account, and the external party. A common trap is assuming that account-level trust alone is sufficient, but the external ID acts as an additional gate. Memory tip: think of the external ID as a secret handshake—without it, the role door stays locked.
This SCS-C02 practice question tests your understanding of identity and access management. 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.
A company uses cross-account roles to allow developers in the 'dev' account to access resources in the 'prod' account. The trust policy in 'prod' allows the 'dev' account to assume the role. The developers have an IAM policy that allows sts:AssumeRole on the role ARN. However, when a developer tries to assume the role via the AWS CLI, they get an error that the role cannot be assumed. The developer can list the role using IAM. What is the MOST likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
The developer's IAM policy does not include sts:AssumeRole.
Why wrong: The policy includes it.
The developer is not providing the required external ID when calling sts:AssumeRole.
External ID is required if the trust policy specifies it.
The developer must use MFA to assume the role.
Why wrong: MFA not required unless specified.
The role ARN specified in the policy is incorrect.
Why wrong: The role exists and can be listed.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The developer is not providing the required external ID when calling sts:AssumeRole.
Option A is correct. The trust policy must allow the specific IAM entity (user or role) or the entire account. If the trust policy allows the account, it should work. But if the trust policy requires an external ID and the developer does not provide it, the assumption will fail. Option B is wrong because the developer's policy allows the action. Option C is wrong because the role exists. Option D is wrong because the developer is not using MFA unless required.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
The developer's IAM policy does not include sts:AssumeRole.
Why it's wrong here
The policy includes it.
The developer is not providing the required external ID when calling sts:AssumeRole.
Why this is correct
External ID is required if the trust policy specifies it.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
The developer must use MFA to assume the role.
Why it's wrong here
MFA not required unless specified.
The role ARN specified in the policy is incorrect.
Why it's wrong here
The role exists and can be listed.
Common exam traps
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Identify which SCS-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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FAQ
Identity and Access Management — This question tests Identity and Access Management — Read the scenario before looking for a memorised answer..
The correct answer is: The developer is not providing the required external ID when calling sts:AssumeRole. — Option A is correct. The trust policy must allow the specific IAM entity (user or role) or the entire account. If the trust policy allows the account, it should work. But if the trust policy requires an external ID and the developer does not provide it, the assumption will fail. Option B is wrong because the developer's policy allows the action. Option C is wrong because the role exists. Option D is wrong because the developer is not using MFA unless required.
Identify which SCS-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 20, 2026
This SCS-C02 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 SCS-C02 exam.
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