Quick Answer
The answer is to use an S3 bucket policy that grants access to the other account. This is the best practice for cross-account S3 access because the bucket policy allows the resource owner to explicitly authorize an external AWS account ID in the Principal element, centralizing permission management without requiring the target account to create an IAM role. On the AWS Certified Security Specialty SCS-C02 exam, this concept tests your understanding of resource-based policies versus identity-based policies; a common trap is assuming an IAM role is always required, but the bucket policy is simpler and more direct for S3 cross-account access. Remember that IAM roles are better for cross-account access to services other than S3, while bucket policies are the native, recommended method for S3 itself. Memory tip: “Bucket policy for bucket access, IAM role for other roles.”
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 company wants to grant cross-account access to an S3 bucket. What is the best practice for managing permissions?
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.
Use an IAM role in the target account
Why wrong: IAM roles are for temporary access, not bucket-level.
Use S3 ACLs with the other account ID
Why wrong: ACLs do not support cross-account by default.
Use an S3 bucket policy that grants access to the other account
Bucket policy can grant cross-account access directly.
Use an SCP to allow access
Why wrong: SCPs are at the organization level.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Use an S3 bucket policy that grants access to the other account
Option C is correct because an S3 bucket policy can explicitly grant cross-account access by specifying the other AWS account ID as the principal in the policy's Principal element. This allows the bucket owner to centrally manage permissions without requiring the target account to create an IAM role, and it works seamlessly with IAM user or role permissions in the external account. It is the recommended best practice for cross-account S3 access as per AWS documentation.
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.
Use an IAM role in the target account
Why it's wrong here
IAM roles are for temporary access, not bucket-level.
Use S3 ACLs with the other account ID
Why it's wrong here
ACLs do not support cross-account by default.
Use an S3 bucket policy that grants access to the other account
Why this is correct
Bucket policy can grant cross-account access directly.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Use an SCP to allow access
Why it's wrong here
SCPs are at the organization level.
Common exam traps
The trap here is that candidates often confuse cross-account access patterns and incorrectly choose IAM roles (Option A) because they think roles are always the best practice, but for S3 buckets, a bucket policy is simpler and more direct for granting access to an entire account.
Detailed technical explanation
Under the hood, an S3 bucket policy is evaluated as a resource-based policy that allows the bucket owner to delegate access to principals in other accounts. The external account's IAM user or role must still have an IAM policy that allows the s3:GetObject or s3:PutObject action, creating a two-step authorization process. A real-world scenario is when a company needs to share log files with a partner account; the bucket policy specifies the partner's account ID, and the partner's IAM users have policies that permit the S3 actions, ensuring secure and auditable access.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Management and Security Governance — This question tests Management and Security Governance — Read the scenario before looking for a memorised answer..
The correct answer is: Use an S3 bucket policy that grants access to the other account — Option C is correct because an S3 bucket policy can explicitly grant cross-account access by specifying the other AWS account ID as the principal in the policy's Principal element. This allows the bucket owner to centrally manage permissions without requiring the target account to create an IAM role, and it works seamlessly with IAM user or role permissions in the external account. It is the recommended best practice for cross-account S3 access as per AWS documentation.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "best". 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.
Read the scenario before looking for a memorised answer.
About these practice questions
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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company wants to grant cross-account access to an S3 bucket owned by Account A to a user in Account B. The bucket policy in Account A allows access from Account B. What additional configuration is required?
easyWhy A: Option B is correct because cross-account access requires both a resource-based policy (bucket policy) and an identity-based policy (IAM user/role policy) in the trusted account. Option A is wrong because the IAM role is not needed, but the user must have permissions. Option C is wrong because SCPs affect all accounts in an organization but are not required. Option D is wrong because the user's permissions are needed.
Variation 2. A security engineer is designing a cross-account access policy. The engineer has an S3 bucket in Account A and wants to grant read access to a user in Account B. Which combination of policies is required?
mediumWhy D: Option D is correct because both a bucket policy in Account A allowing the user and an IAM policy in Account B granting s3:GetObject are required. Option A is wrong because bucket policy alone is insufficient. Option B is wrong because IAM policy alone is insufficient. Option C is wrong because ACLs are legacy and less secure.
Variation 3. A security engineer needs to grant cross-account read access to an S3 bucket in Account A to a user in Account B. What is the correct combination of actions?
easyWhy D: Cross-account S3 access requires both a bucket policy in the resource account (Account A) that explicitly grants the cross-account principal (the user in Account B) the s3:GetObject action, and an IAM policy attached to the user in Account B that allows the same action. This two-way authorization is necessary because the bucket policy controls access to the S3 resource, while the IAM policy controls the user's permissions to initiate the request. Without both, the request will be denied by either the resource-based policy or the identity-based policy.
Last reviewed: Jun 24, 2026
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