The correct answer is that the bucket policy’s explicit deny overrides the IAM policy’s allow. This happens because AWS evaluates all policies together, and any explicit deny in a resource-based policy, such as an S3 bucket policy, takes precedence over an identity-based IAM policy that grants permission. In this scenario, the bucket policy denies PutObject unless the encryption is aws:kms, while the IAM policy requires AES256 encryption, creating a direct conflict that results in an AccessDenied error. On the CompTIA Cloud+ CV0-004 exam, this tests your understanding of policy evaluation logic, especially how encryption requirements in bucket policies can silently block uploads even when IAM allows them. A common trap is assuming IAM permissions alone are sufficient, but bucket policies act as a separate gatekeeper. Remember the memory tip: “Deny always wins” — when troubleshooting S3 access denied due to IAM and bucket policy encryption conflict, always check if a resource-based deny is blocking the action before blaming the IAM policy.
CV0-004 Deployment Practice Question
This CV0-004 practice question tests your understanding of deployment. 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 developer is trying to upload an object to S3 bucket 'example-bucket' using the IAM policy shown. The upload fails with an AccessDenied error. Which of the following is the MOST likely reason?
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 has a deny that overrides this IAM policy.
Option C is correct because the bucket policy denies PutObject unless the encryption is aws:kms, while the IAM policy requires AES256. The bucket policy's explicit deny overrides the IAM allow, causing the failure.
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 IAM policy requires server-side encryption with AES256, but the upload request did not specify that header.
Why it's wrong here
Even if the header is missing, the bucket policy would still deny, but the most direct cause is the conflicting bucket policy.
✓
The bucket policy has a deny that overrides this IAM policy.
Why this is correct
The bucket policy denies PutObject unless encryption is aws:kms, which conflicts with the IAM policy's AES256 requirement, resulting in a deny.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The developer's user is not in the same account as the bucket.
Why it's wrong here
Cross-account access can be allowed with proper policies; the exhibit does not indicate account mismatch.
✗
The IAM policy does not grant the s3:ListBucket permission.
Why it's wrong here
ListBucket is not required for uploads; the error is AccessDenied on PutObject, not ListBucket.
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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
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 CV0-004 ACL questions on filtering logic and placement.
Deployment — This question tests Deployment — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The bucket policy has a deny that overrides this IAM policy. — Option C is correct because the bucket policy denies PutObject unless the encryption is aws:kms, while the IAM policy requires AES256. The bucket policy's explicit deny overrides the IAM allow, causing the failure.
What should I do if I get this CV0-004 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 CV0-004 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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