The answer is that the bucket policy is missing permissions for CloudTrail to perform `s3:GetBucketAcl` and `s3:PutBucketAcl`. CloudTrail requires these ACL-related actions to verify and configure the bucket’s access control list before it can deliver logs, whereas VPC Flow Logs do not need these permissions—they only require `s3:PutObject` and `s3:GetBucketAcl` for delivery. On the AWS Certified Security Specialty SCS-C02 exam, this distinction tests your understanding of service-specific bucket policy requirements; a common trap is assuming that if one logging service works, the policy is fully correct for all. Remember that CloudTrail performs an ACL check during trail creation and log delivery, while Flow Logs skip that step. Memory tip: “CloudTrail checks the ACL, Flow Logs just fill the well.”
SCS-C02 Security Logging and Monitoring Practice Question
This SCS-C02 practice question tests your understanding of security logging and monitoring. 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 security engineer has created an S3 bucket policy to allow AWS CloudTrail and VPC Flow Logs to deliver logs to the bucket. However, CloudTrail logs are not being delivered, but VPC Flow Logs are delivered successfully. 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 does not grant CloudTrail permission to perform 's3:GetBucketAcl' and 's3:PutBucketAcl'.
The service principal for CloudTrail is `cloudtrail.amazonaws.com`, which is correct, so the issue is likely that the CloudTrail trail's S3 bucket is not configured correctly, or the bucket policy does not include the necessary permissions for CloudTrail to verify the bucket. However, given that VPC Flow Logs work, the issue might be that the CloudTrail trail is not using the correct bucket name or prefix. But the question focuses on the policy; the policy seems correct for both. The most common issue is that CloudTrail requires the bucket to have a specific ACL or the policy to allow `s3:GetBucketAcl` and `s3:PutBucketAcl`. Option D is correct. Option A is wrong because the service principal is correct. Option B is wrong because the condition is fine. Option C is wrong because the principal is correct. Option D addresses a common missing permission.
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 principal is set to a service instead of an AWS account.
Why it's wrong here
CloudTrail uses service principal to write logs.
✗
The condition 's3:x-amz-acl' is misspelled.
Why it's wrong here
The condition is correctly spelled.
✗
The service principal in the policy is incorrect for CloudTrail.
Why it's wrong here
The service principal 'cloudtrail.amazonaws.com' is correct.
✓
The bucket policy does not grant CloudTrail permission to perform 's3:GetBucketAcl' and 's3:PutBucketAcl'.
Why this is correct
CloudTrail needs these permissions to verify bucket ownership.
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 SCS-C02 ACL questions on filtering logic and placement.
Security Logging and Monitoring — This question tests Security Logging and Monitoring — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The bucket policy does not grant CloudTrail permission to perform 's3:GetBucketAcl' and 's3:PutBucketAcl'. — The service principal for CloudTrail is `cloudtrail.amazonaws.com`, which is correct, so the issue is likely that the CloudTrail trail's S3 bucket is not configured correctly, or the bucket policy does not include the necessary permissions for CloudTrail to verify the bucket. However, given that VPC Flow Logs work, the issue might be that the CloudTrail trail is not using the correct bucket name or prefix. But the question focuses on the policy; the policy seems correct for both. The most common issue is that CloudTrail requires the bucket to have a specific ACL or the policy to allow `s3:GetBucketAcl` and `s3:PutBucketAcl`. Option D is correct. Option A is wrong because the service principal is correct. Option B is wrong because the condition is fine. Option C is wrong because the principal is correct. Option D addresses a common missing permission.
What should I do if I get this SCS-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 SCS-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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