The answer is that the bucket does not have a default encryption configuration set to SSE-KMS. This is the most likely cause because S3 default encryption settings must be explicitly enabled on the bucket to enforce server-side encryption when no encryption header is provided during upload. Without this configuration, S3 treats the object as unencrypted by default, allowing the upload to succeed without any encryption at rest. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding that default encryption is not automatically applied—it must be configured, and bucket policies alone cannot retroactively encrypt objects; they can only deny unencrypted uploads, which would cause the upload to fail entirely. A common trap is confusing bucket policies with default encryption settings, but remember: policies block or allow, while default encryption silently applies encryption. Memory tip: "No header, no encryption—unless default encryption is set."
DVA-C02 Security Practice Question
This DVA-C02 practice question tests your understanding of security. 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.
A company stores sensitive data in an S3 bucket that must be encrypted at rest. The security team requires that all objects uploaded to the bucket are automatically encrypted using server-side encryption with AWS KMS (SSE-KMS). A developer uploads an object without specifying any encryption header. The upload succeeds, but the object is not encrypted. 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.
The bucket policy denies uploads without the x-amz-server-side-encryption header, but the developer's IAM user has permission to override the bucket policy.
Why wrong: If the bucket policy denies, the upload would fail.
B
The KMS key policy does not allow the IAM user to encrypt with that key.
Why wrong: If the key policy denies, the upload would fail with an access denied error.
C
The S3 bucket has default encryption disabled.
Why wrong: Default encryption disabled means no encryption is applied, but the question asks for the most likely cause.
D
The bucket does not have a default encryption configuration set to SSE-KMS.
Without default encryption, objects uploaded without encryption headers remain unencrypted.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The bucket does not have a default encryption configuration set to SSE-KMS.
Option D is correct because S3 default encryption must be explicitly enabled on the bucket to enforce SSE-KMS when no encryption header is provided. Option A is wrong because bucket policies cannot enforce encryption headers retroactively; they can deny PutObject without encryption, but the upload would fail, not succeed unencrypted. Option B is wrong because the bucket policy does not block the upload. Option C is wrong because the KMS key policy does not affect default encryption enforcement.
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 denies uploads without the x-amz-server-side-encryption header, but the developer's IAM user has permission to override the bucket policy.
Why it's wrong here
If the bucket policy denies, the upload would fail.
✗
The KMS key policy does not allow the IAM user to encrypt with that key.
Why it's wrong here
If the key policy denies, the upload would fail with an access denied error.
✗
The S3 bucket has default encryption disabled.
Why it's wrong here
Default encryption disabled means no encryption is applied, but the question asks for the most likely cause.
✓
The bucket does not have a default encryption configuration set to SSE-KMS.
Why this is correct
Without default encryption, objects uploaded without encryption headers remain unencrypted.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
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 DVA-C02 ACL questions on filtering logic and placement.
Security — This question tests Security — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The bucket does not have a default encryption configuration set to SSE-KMS. — Option D is correct because S3 default encryption must be explicitly enabled on the bucket to enforce SSE-KMS when no encryption header is provided. Option A is wrong because bucket policies cannot enforce encryption headers retroactively; they can deny PutObject without encryption, but the upload would fail, not succeed unencrypted. Option B is wrong because the bucket policy does not block the upload. Option C is wrong because the KMS key policy does not affect default encryption enforcement.
What should I do if I get this DVA-C02 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 DVA-C02 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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