The answer is that a bucket policy explicitly denying the s3:PutObject action is the most likely cause of the Access Denied error. This is because IAM policies grant permissions, but any explicit deny in a bucket policy overrides those allows, regardless of what the IAM policy permits. For S3 migration troubleshooting, you must always check both the IAM user policy and the target bucket’s resource-based policy, as a deny statement will block the upload even if the IAM policy correctly specifies the resource ARN as 'arn:aws:s3:::example-bucket/*'. On the AWS Certified SAP on AWS Specialty PAS-C01 exam, this scenario tests your understanding of the evaluation logic where explicit denies take precedence over allows, a common trap where candidates focus only on the IAM policy and miss the bucket policy. A key memory tip is “Deny always wins”—when debugging S3 migration Access Denied errors, always inspect the bucket policy first for any explicit deny statements.
PAS-C01 Migration Practice Question
This PAS-C01 practice question tests your understanding of migration. 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.
Refer to the exhibit. A company is migrating its data to Amazon S3. The security team has provided this IAM policy for the migration user. However, the migration fails with an Access Denied error when trying to upload files to the bucket. What is the most likely cause?
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 bucket policy explicitly denies the s3:PutObject action for the IAM user.
The policy specifies the resource as 'arn:aws:s3:::example-bucket/*' for s3:PutObject. This resource ARN is correct for object-level operations. However, the error could be due to bucket policy that denies the upload, or the IAM user lacks s3:PutObjectAcl or other permissions. But the most likely cause given the policy is that the bucket policy explicitly denies the action. Option A is wrong because the policy does allow s3:PutObject. Option B is wrong because there is no encryption requirement in the policy. Option C is wrong because the policy does not include kms:Decrypt, but if encryption is required, the policy would need additional actions. Option D is correct because a bucket policy with a deny statement would override the allow.
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 bucket policy explicitly denies the s3:PutObject action for the IAM user.
Why this is correct
A bucket policy with a deny statement would override the IAM allow, causing Access Denied.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The IAM policy does not include s3:PutObject permission.
Why it's wrong here
The policy clearly includes s3:PutObject.
✗
The IAM policy does not include kms:Decrypt permission.
Why it's wrong here
S3 server-side encryption with S3 managed keys (SSE-S3) does not require KMS permissions.
✗
The bucket has default encryption enabled and the IAM user does not have permission to use the encryption key.
Why it's wrong here
Default encryption does not require additional permissions for the uploading user; the bucket can encrypt objects server-side.
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 PAS-C01 ACL questions on filtering logic and placement.
Migration — This question tests Migration — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The bucket policy explicitly denies the s3:PutObject action for the IAM user. — The policy specifies the resource as 'arn:aws:s3:::example-bucket/*' for s3:PutObject. This resource ARN is correct for object-level operations. However, the error could be due to bucket policy that denies the upload, or the IAM user lacks s3:PutObjectAcl or other permissions. But the most likely cause given the policy is that the bucket policy explicitly denies the action. Option A is wrong because the policy does allow s3:PutObject. Option B is wrong because there is no encryption requirement in the policy. Option C is wrong because the policy does not include kms:Decrypt, but if encryption is required, the policy would need additional actions. Option D is correct because a bucket policy with a deny statement would override the allow.
What should I do if I get this PAS-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 PAS-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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