The correct answer is a bucket policy in Account A granting s3:GetObject to Account B combined with an IAM policy in Account B allowing s3:GetObject. This combination works because cross-account S3 bucket access requires a two-way authorization: the resource-based policy (the bucket policy) must explicitly grant the target account or its users access to the bucket, and the accessing account must have an identity-based policy that permits the same action. Without the IAM policy in Account B, even if the bucket policy allows access, users in Account B have no permission to perform the GetObject action. On the AWS Certified Security Specialty SCS-C02 exam, this concept tests your understanding of the shared responsibility model for cross-account permissions and often appears as a trap where one policy is missing. A common mistake is assuming a bucket policy alone is sufficient, but the accessing account’s IAM policy is mandatory. Memory tip: think of it as a “handshake” — the bucket policy opens the door, and the IAM policy gives the user the key to walk through.
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. 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 company wants to allow cross-account access to an S3 bucket. The bucket owner (Account A) wants to grant read-only access to users in Account B. Which combination of policies is required?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A bucket policy in Account A granting s3:GetObject to Account B and an IAM policy in Account B allowing s3:GetObject
Option A is correct because cross-account access requires both a bucket policy granting access and an IAM policy in the accessing account allowing the action. Option B is wrong because an IAM role in Account A would require users to assume the role. Option C is wrong because a bucket ACL is not the recommended method and does not work with IAM policies alone. Option D is wrong because the accessing account must have an IAM policy to allow the action.
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.
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A bucket ACL in Account A granting READ access to Account B
Why it's wrong here
ACLs are legacy and do not integrate with IAM policies effectively for cross-account.
✓
A bucket policy in Account A granting s3:GetObject to Account B and an IAM policy in Account B allowing s3:GetObject
Why this is correct
Both policies are needed: the bucket policy allows cross-account access, and the IAM policy allows the user to perform the action.
Related concept
Static NAT maps one inside address to one outside address.
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An IAM policy in Account A that allows s3:GetObject
Why it's wrong here
The bucket policy is needed in Account A; the IAM policy is needed in Account B.
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An IAM role in Account B that grants s3:GetObject to Account A
Why it's wrong here
The IAM role should be in Account A for cross-account access.
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.
Infrastructure Security — This question tests Infrastructure Security — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: A bucket policy in Account A granting s3:GetObject to Account B and an IAM policy in Account B allowing s3:GetObject — Option A is correct because cross-account access requires both a bucket policy granting access and an IAM policy in the accessing account allowing the action. Option B is wrong because an IAM role in Account A would require users to assume the role. Option C is wrong because a bucket ACL is not the recommended method and does not work with IAM policies alone. Option D is wrong because the accessing account must have an IAM policy to allow the action.
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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