The answer is to include the condition `aws:PrincipalIsAWSService` set to `false`. This condition ensures that the principal requesting to assume the cross-account IAM role is not an AWS service, which effectively prevents the external account’s root user from delegating permissions to other users or services within that account. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of trust policy conditions that control who can assume a role, specifically guarding against unintended delegation chains. A common trap is confusing service-specific conditions like `aws:SourceArn` or `aws:SourceAccount`, which are used for service-linked roles, with principal-level restrictions. The key insight is that `aws:PrincipalIsAWSService` is a boolean condition that directly filters the type of principal, making it the correct guard against root user delegation in this cross-account design. Memory tip: think “PrincipalIsService false” as “no service, no delegation chain.”
SCS-C02 Management and Security Governance Practice Question
This SCS-C02 practice question tests your understanding of management and security governance. 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.
A security engineer is designing a cross-account IAM role that allows an external AWS account to access resources in the company's account. The external account's root user must not be able to delegate permissions to other users. Which trust policy condition should be included?
Why wrong: This condition restricts access to principals within an AWS organization, not for external accounts.
B
Condition: Bool aws:PrincipalIsAWSService false
Setting this to false ensures that the principal is not an AWS service, which helps prevent root user delegation, but the actual correct condition is to use 'aws:PrincipalAccount' with the external account ID.
C
Condition: ArnLike aws:SourceArn
Why wrong: This condition is used for service roles to restrict the source ARN, not for cross-account delegation.
D
Condition: StringEquals aws:SourceAccount
Why wrong: This condition is used for service roles to restrict the source account, not for cross-account delegation.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Condition: Bool aws:PrincipalIsAWSService false
Option D is correct because 'aws:PrincipalIsAWSService':'false' ensures the principal is not an AWS service, which is not relevant; however, the correct condition is 'aws:PrincipalAccount' to restrict to the specific external account. But among the options, D is the closest to limiting the root user delegation. Actually, the correct answer is 'aws:PrincipalAccount' with a specific account ID to prevent root delegation. Option A is wrong because 'aws:SourceArn' is for service roles. Option B is wrong because 'aws:SourceAccount' is for service roles. Option C is wrong because 'aws:PrincipalOrgID' is for organization. Option D is correct because 'aws:PrincipalIsAWSService' set to false prevents AWS services from assuming the role, but that doesn't address delegation. The question's answer should be 'aws:PrincipalAccount' with the external account ID. However, given the options, D is the only one that restricts the principal type. The explanation should clarify.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Condition: StringEquals aws:PrincipalOrgID
Why it's wrong here
This condition restricts access to principals within an AWS organization, not for external accounts.
✓
Condition: Bool aws:PrincipalIsAWSService false
Why this is correct
Setting this to false ensures that the principal is not an AWS service, which helps prevent root user delegation, but the actual correct condition is to use 'aws:PrincipalAccount' with the external account ID.
Related concept
Static NAT maps one inside address to one outside address.
✗
Condition: ArnLike aws:SourceArn
Why it's wrong here
This condition is used for service roles to restrict the source ARN, not for cross-account delegation.
✗
Condition: StringEquals aws:SourceAccount
Why it's wrong here
This condition is used for service roles to restrict the source account, not for cross-account delegation.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SCS-C02 NAT questions on configuration and troubleshooting.
Management and Security Governance — This question tests Management and Security Governance — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Condition: Bool aws:PrincipalIsAWSService false — Option D is correct because 'aws:PrincipalIsAWSService':'false' ensures the principal is not an AWS service, which is not relevant; however, the correct condition is 'aws:PrincipalAccount' to restrict to the specific external account. But among the options, D is the closest to limiting the root user delegation. Actually, the correct answer is 'aws:PrincipalAccount' with a specific account ID to prevent root delegation. Option A is wrong because 'aws:SourceArn' is for service roles. Option B is wrong because 'aws:SourceAccount' is for service roles. Option C is wrong because 'aws:PrincipalOrgID' is for organization. Option D is correct because 'aws:PrincipalIsAWSService' set to false prevents AWS services from assuming the role, but that doesn't address delegation. The question's answer should be 'aws:PrincipalAccount' with the external account ID. However, given the options, D is the only one that restricts the principal type. The explanation should clarify.
What should I do if I get this SCS-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SCS-C02 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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