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Design Secure Architectures →hardMultiple ChoiceObjective-mapped

SAA-C03 Design Secure Architectures Practice Question

This SAA-C03 practice question tests your understanding of design secure architectures. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.

Exhibit

Current trust policy in Account A:
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {"AWS": "arn:aws:iam::444455556666:root"},
      "Action": "sts:AssumeRole"
    }
  ]
}

CloudTrail entry from Account A:
{
  "eventSource": "sts.amazonaws.com",
  "eventName": "AssumeRole",
  "userIdentity": {
    "type": "AssumedRole",
    "arn": "arn:aws:sts::444455556666:assumed-role/OtherRole/automation"
  },
  "errorCode": "AccessDenied"
}

Based on the exhibit, a workload in Account B must assume a role in Account A. Security requires that only the specific role arn:aws:iam::444455556666:role/PipelineExecRole can assume it, and only when the caller supplies the external ID acct-b-prod-7788. Which change best satisfies the requirement with the least privilege?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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 1hardmultiple choice

Full question →

Exhibit

Current trust policy in Account A:
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {"AWS": "arn:aws:iam::444455556666:root"},
      "Action": "sts:AssumeRole"
    }
  ]
}

CloudTrail entry from Account A:
{
  "eventSource": "sts.amazonaws.com",
  "eventName": "AssumeRole",
  "userIdentity": {
    "type": "AssumedRole",
    "arn": "arn:aws:sts::444455556666:assumed-role/OtherRole/automation"
  },
  "errorCode": "AccessDenied"
}

A
Keep the root principal and add an aws:PrincipalTag condition in the trust policy to require the tag acct-b-prod-7788.
Why wrong: Principal tags can help with authorization, but they do not ensure that only one exact role in Account B can call STS. Any principal that can supply the tag might still satisfy the condition. This does not provide the required caller-specific trust boundary.
B
Replace the principal with arn:aws:iam::444455556666:role/PipelineExecRole and add a StringEquals condition on sts:ExternalId = acct-b-prod-7788.
This change directly restricts trust to one named role in Account B and adds a confused-deputy defense with the external ID. The role trust policy is the correct place to control who can assume the role, and the external ID ensures only the expected caller can complete the STS request.
C
Attach a permission boundary to the role in Account A so that only PipelineExecRole can use it.
Why wrong: Permission boundaries limit the maximum permissions a role can have after it is assumed, but they do not control who is trusted to assume the role. The trust policy, not the permission boundary, determines which external principal can call sts:AssumeRole.
D
Add an SCP in Account B that allows sts:AssumeRole only for PipelineExecRole.
Why wrong: An SCP can constrain identities in Account B, but it cannot by itself grant trust on the role in Account A. The trust policy in Account A must still explicitly allow the correct principal and should include the external ID condition for secure cross-account access.

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

✓

Replace the principal with arn:aws:iam::444455556666:role/PipelineExecRole and add a StringEquals condition on sts:ExternalId = acct-b-prod-7788.

Option B is correct because it explicitly restricts the trust policy principal to the specific IAM role ARN `arn:aws:iam::444455556666:role/PipelineExecRole` and adds a `StringEquals` condition on `sts:ExternalId` set to `acct-b-prod-7788`. This satisfies the security requirement by ensuring only that exact role can assume the role in Account A, and only when the correct external ID is provided, following the principle of least privilege.

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.

✗
Keep the root principal and add an aws:PrincipalTag condition in the trust policy to require the tag acct-b-prod-7788.
Why it's wrong here
Principal tags can help with authorization, but they do not ensure that only one exact role in Account B can call STS. Any principal that can supply the tag might still satisfy the condition. This does not provide the required caller-specific trust boundary.
✓
Replace the principal with arn:aws:iam::444455556666:role/PipelineExecRole and add a StringEquals condition on sts:ExternalId = acct-b-prod-7788.
Why this is correct
This change directly restricts trust to one named role in Account B and adds a confused-deputy defense with the external ID. The role trust policy is the correct place to control who can assume the role, and the external ID ensures only the expected caller can complete the STS request.
Clue confirmation
The clue words "best", "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Attach a permission boundary to the role in Account A so that only PipelineExecRole can use it.
Why it's wrong here
Permission boundaries limit the maximum permissions a role can have after it is assumed, but they do not control who is trusted to assume the role. The trust policy, not the permission boundary, determines which external principal can call sts:AssumeRole.
✗
Add an SCP in Account B that allows sts:AssumeRole only for PipelineExecRole.
Why it's wrong here
An SCP can constrain identities in Account B, but it cannot by itself grant trust on the role in Account A. The trust policy in Account A must still explicitly allow the correct principal and should include the external ID condition for secure cross-account access.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often confuse the trust policy's `Principal` element with permission boundaries or SCPs, mistakenly thinking those can restrict who can assume a role, when in fact only the trust policy controls the assumption, and the external ID condition is required to prevent confused deputy attacks.

Detailed technical explanation

How to think about this question

The `sts:ExternalId` condition is a critical security measure for cross-account role assumption, especially when the trusting account (Account A) needs to verify the purpose of the request from a third party (Account B). Under the hood, AWS evaluates the trust policy's `Principal` element first to determine if the caller is allowed, then checks all conditions, including `sts:ExternalId`, which must match exactly and is case-sensitive. In real-world scenarios, this prevents the confused deputy problem where an attacker in Account B could trick Account A into granting access by reusing a role ARN without the intended context.

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 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

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: Replace the principal with arn:aws:iam::444455556666:role/PipelineExecRole and add a StringEquals condition on sts:ExternalId = acct-b-prod-7788. — Option B is correct because it explicitly restricts the trust policy principal to the specific IAM role ARN `arn:aws:iam::444455556666:role/PipelineExecRole` and adds a `StringEquals` condition on `sts:ExternalId` set to `acct-b-prod-7788`. This satisfies the security requirement by ensuring only that exact role can assume the role in Account A, and only when the correct external ID is provided, following the principle of least privilege.

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: "best", "least". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Last reviewed: Jun 11, 2026

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