Troubleshooting IAM Policy for S3 Backup Upload Failure with KMS Encryption
This PAS-C01 practice question tests your understanding of operations and maintenance. 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.
An SAP administrator created the IAM policy shown for a backup script. The script fails when trying to upload a backup to S3. What is the likely cause?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The KMS key ARN is malformed; it contains extra characters.
The correct answer is D because the KMS key ARN in the IAM policy is malformed (contains extra characters). When the backup script attempts to upload to S3 with server-side encryption using KMS (SSE-KMS), S3 needs to decrypt the object using the KMS key. If the key ARN is invalid, the kms:Decrypt permission cannot be evaluated, causing the upload to fail. Option A is incorrect because for PutObject, the resource must be the object ARN (arn:aws:s3:::sap-backup-bucket/*), not the bucket itself. Option B is incorrect because ec2:Describe* actions do not interfere with S3 operations. Option C is incorrect because the s3:* action, while broad, is permitted on the specified objects, and there is no indication of a restrictive bucket policy.
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 resource for S3 should include the bucket itself (arn:aws:s3:::sap-backup-bucket).
Why it's wrong here
PutObject requires object ARN, which is correct.
✗
The ec2:Describe* action is not required and causes a conflict.
Why it's wrong here
Unused actions do not cause failures.
✗
The s3:* action is too broad and is denied by an S3 bucket policy.
Why it's wrong here
The action is allowed, bucket policy might override but not necessarily.
✓
The KMS key ARN is malformed; it contains extra characters.
Why this is correct
The key ARN has a typo with 'a123b4cd56ef' instead of proper format.
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.
Quick reference
AWS S3 Storage Class Comparison
Storage Class
Min Duration
Retrieval
Use Case
S3 Standard
None
Immediate
Frequently accessed data
S3 Standard-IA
30 days
Immediate
Infrequent access, rapid retrieval
S3 One Zone-IA
30 days
Immediate
Non-critical infrequent data
S3 Intelligent-Tiering
None
Immediate–hours
Unknown or changing access patterns
S3 Glacier Instant
90 days
Milliseconds
Archive with instant retrieval
S3 Glacier Flexible
90 days
Minutes–hours
Archive, flexible retrieval
S3 Glacier Deep Archive
180 days
Hours
Long-term compliance archive
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.
Operations and Maintenance — This question tests Operations and Maintenance — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The KMS key ARN is malformed; it contains extra characters. — The correct answer is D because the KMS key ARN in the IAM policy is malformed (contains extra characters). When the backup script attempts to upload to S3 with server-side encryption using KMS (SSE-KMS), S3 needs to decrypt the object using the KMS key. If the key ARN is invalid, the kms:Decrypt permission cannot be evaluated, causing the upload to fail. Option A is incorrect because for PutObject, the resource must be the object ARN (arn:aws:s3:::sap-backup-bucket/*), not the bucket itself. Option B is incorrect because ec2:Describe* actions do not interfere with S3 operations. Option C is incorrect because the s3:* action, while broad, is permitted on the specified objects, and there is no indication of a restrictive bucket policy.
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.
What is the key concept behind this question?
Standard ACLs match source addresses.
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