Quick Answer
The answer is that the IAM user in the other account lacks the necessary identity-based permissions. This is because cross-account S3 access requires a two-step authorization: the target account’s bucket policy must grant access to the external user, and the external user’s own IAM policy must explicitly allow the S3 action, such as s3:GetObject, on that bucket. Without both policies aligned, the request is denied by the requesting account’s IAM evaluation, even if the bucket policy appears permissive. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of the shared responsibility model for cross-account access, often appearing as a trick where candidates focus only on the bucket policy. A common trap is assuming a resource-based policy alone is sufficient, but identity-based policies in the source account are equally mandatory. Remember the two-key rule: the bucket policy unlocks the door from the target side, but the IAM user policy must turn the key from the source side.
This DEA-C01 practice question tests your understanding of data security and 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 data engineer notices that an S3 bucket policy allows access to a user from another AWS account, but the access is being denied. What could be the reason?
The bucket policy does not include KMS permissions
Why wrong: KMS is not required for S3 access.
The other account's IAM user does not have permissions to access the bucket
Cross-account access requires IAM permissions in the other account.
S3 does not support cross-account access
Why wrong: S3 supports cross-account access via bucket policies.
The bucket is in a different region
Why wrong: Cross-region access is allowed.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The other account's IAM user does not have permissions to access the bucket
For cross-account S3 access to succeed, both the bucket policy (resource-based policy) and the IAM user policy (identity-based policy) in the other account must grant the necessary permissions. Option B is correct because even if the bucket policy allows access from the other account, the IAM user in that account must have an explicit IAM policy that permits the S3 action (e.g., s3:GetObject) on the bucket. Without this, the request is denied by the other account's own IAM evaluation.
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.
The bucket policy does not include KMS permissions
Why it's wrong here
KMS is not required for S3 access.
The other account's IAM user does not have permissions to access the bucket
Why this is correct
Cross-account access requires IAM permissions in the other account.
Related concept
Read the scenario before looking for a memorised answer.
S3 does not support cross-account access
Why it's wrong here
S3 supports cross-account access via bucket policies.
The bucket is in a different region
Why it's wrong here
Cross-region access is allowed.
Common exam traps
The trap here is that candidates assume a bucket policy alone is sufficient for cross-account access, forgetting that the requesting account's IAM user must also have explicit permissions, which is a classic AWS cross-account authorization nuance.
Detailed technical explanation
Under the hood, AWS evaluates both the bucket policy and the requester's IAM policy in a union model: the request is allowed only if both policies grant the action (unless the bucket policy explicitly allows anonymous access). A common real-world scenario is when a data engineer sets a bucket policy allowing 'Principal': { 'AWS': 'arn:aws:iam::OTHER-ACCOUNT-ID:root' } but forgets that the IAM user in the other account needs an inline or managed policy like 's3:GetObject' on the bucket ARN. The IAM policy evaluation happens first in the other account, and if it denies or lacks the permission, the request never reaches the bucket policy.
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
Data Security and Governance — This question tests Data Security and Governance — Read the scenario before looking for a memorised answer..
The correct answer is: The other account's IAM user does not have permissions to access the bucket — For cross-account S3 access to succeed, both the bucket policy (resource-based policy) and the IAM user policy (identity-based policy) in the other account must grant the necessary permissions. Option B is correct because even if the bucket policy allows access from the other account, the IAM user in that account must have an explicit IAM policy that permits the S3 action (e.g., s3:GetObject) on the bucket. Without this, the request is denied by the other account's own IAM evaluation.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This DEA-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DEA-C01 exam.
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