The correct answer is an IAM role in Account A with a trust policy for Account B. This configuration works because cross-account S3 access using IAM role relies on the trusting account (Account A) creating a role that explicitly lists Account B as a trusted entity in its trust policy, which then allows a principal in Account B to assume that role via the AWS Security Token Service (STS). On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of the distinction between resource-based policies (like S3 bucket policies) and identity-based policies with trust relationships—a common trap is assuming a bucket policy alone suffices, but without the role’s trust policy and the sts:AssumeRole permission in Account B, the access chain breaks. Remember the key memory tip: the role lives in the account that owns the resource (Account A), not in the account that needs access.
SCS-C02 Identity and Access Management Practice Question
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 security engineer needs to grant cross-account access to an S3 bucket in Account A to a role in Account B. Which combination of IAM entities must be configured?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
IAM role in Account A with trust policy for Account B
Cross-account access requires an IAM role in the trusting account (Account A) with a trust policy that allows the trusted account (Account B) to assume it, and an IAM policy in Account B that allows the user or role to call sts:AssumeRole. Option C is correct. Option A is wrong because the bucket policy alone is not sufficient; the role must also allow the action. Option B is wrong because the role is in Account A, not Account B. Option D is wrong because an IAM user in Account B cannot directly access a role in Account A without assuming it.
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.
✗
Bucket policy in Account A and IAM user policy in Account B
Why it's wrong here
Bucket policy allows access, but Account B still needs a role to assume.
✗
IAM role in Account B with trust policy for Account A
Why it's wrong here
The role should be in Account A, not Account B.
✓
IAM role in Account A with trust policy for Account B
Why this is correct
The role in Account A trusts Account B to assume it.
Related concept
Static NAT maps one inside address to one outside address.
✗
IAM user in Account B with permissions to the bucket
Why it's wrong here
An IAM user cannot directly access resources in another account without assuming a role.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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.
Identity and Access Management — This question tests Identity and Access Management — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: IAM role in Account A with trust policy for Account B — Cross-account access requires an IAM role in the trusting account (Account A) with a trust policy that allows the trusted account (Account B) to assume it, and an IAM policy in Account B that allows the user or role to call sts:AssumeRole. Option C is correct. Option A is wrong because the bucket policy alone is not sufficient; the role must also allow the action. Option B is wrong because the role is in Account A, not Account B. Option D is wrong because an IAM user in Account B cannot directly access a role in Account A without assuming it.
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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Question Discussion
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