The answer is that the object is owned by a different AWS account, and the bucket owner has not been granted access. This is because, by default, when an object is uploaded to an S3 bucket by a different AWS account, that uploading account retains ownership of the object, and the bucket owner does not automatically receive any permissions to it—even if the bucket owner has a policy granting s3:GetObject to their own IAM users. For the download to succeed, the object owner must explicitly grant the bucket owner access, typically via an object ACL or a bucket policy that the uploading account accepts. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this scenario tests your understanding of S3 cross-account object access denied errors, often appearing as a trap where candidates assume bucket-level permissions are sufficient. A common memory tip: bucket policy controls the door, but object ownership controls the lock—without the object owner’s key, you stay denied.
MLS-C01 Data Engineering Practice Question
This MLS-C01 practice question tests your understanding of data engineering. 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.
Network Topology
A data engineer runs the CLI command to download an object from S3. The bucket owner is 123456789012, and the engineer's IAM user has s3:GetObject permission on the bucket. The object was uploaded by a different AWS account. What is the MOST likely reason for the AccessDenied error?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The object is owned by a different AWS account, and the bucket owner has not been granted access
By default, objects uploaded by another account are owned by the uploading account, and the bucket owner does not have access unless explicitly granted via bucket policy or ACL. The --expected-bucket-owner parameter only checks the bucket owner, not the object. The engineer's permissions are on the bucket, but the object is owned by another account, so the bucket owner needs additional permissions.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The --expected-bucket-owner parameter is incorrect
Why it's wrong here
The parameter is for bucket owner, not object owner.
✓
The object is owned by a different AWS account, and the bucket owner has not been granted access
Why this is correct
Object ACLs or bucket policy must grant access to bucket owner.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The bucket policy denies access to the engineer's IAM user
Why it's wrong here
There is no indication of a Deny.
✗
The IAM policy does not allow s3:GetObject for that specific key
Why it's wrong here
The policy allows GetObject on the bucket, but object ownership matters.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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 ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related MLS-C01 ACL questions on filtering logic and placement.
Data Engineering — This question tests Data Engineering — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The object is owned by a different AWS account, and the bucket owner has not been granted access — By default, objects uploaded by another account are owned by the uploading account, and the bucket owner does not have access unless explicitly granted via bucket policy or ACL. The --expected-bucket-owner parameter only checks the bucket owner, not the object. The engineer's permissions are on the bucket, but the object is owned by another account, so the bucket owner needs additional permissions.
What should I do if I get this MLS-C01 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related MLS-C01 ACL questions on filtering logic and placement.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Question Discussion
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