- A
"Deny" effect with "StringNotEquals" on "aws:SourceIdentity"
Why wrong: SourceIdentity is not a standard condition for authentication.
- B
"Deny" effect with "aws:SourceIp" condition
Why wrong: This restricts by IP but does not require IAM credentials.
- C
"Deny" effect with "Null" condition on "aws:PrincipalArn"
Denies access when the principal ARN is null (anonymous requests).
- D
"Allow" effect with "Referer" condition
Why wrong: Referer can be spoofed and does not enforce IAM credentials.
Question 1,093 of 1,748
How to Enforce IAM Authentication for S3 Bucket Access Using Bucket Policy
This SCS-C02 practice question tests your understanding of identity and access management. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 has an S3 bucket that stores sensitive data. The security team requires that all access to the bucket be logged in AWS CloudTrail and that all requests must be authenticated using IAM credentials. Which S3 bucket policy statement should be added to enforce these requirements?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
"Deny" effect with "Null" condition on "aws:PrincipalArn"
Option C is correct because a bucket policy with a Deny effect and a Null condition on aws:PrincipalArn will block any request that does not have a valid IAM principal ARN (i.e., anonymous requests). This ensures that only requests authenticated with IAM credentials (users/roles) are allowed. Option A uses aws:SourceIdentity which is not relevant for enforcing IAM authentication. Option B uses aws:SourceIp which restricts by IP address but does not enforce IAM credentials. Option D uses aws:Referer which is based on HTTP referer header and does not enforce authentication. To also enforce CloudTrail logging, a separate condition could be added, but the question specifically asks for enforcing IAM credentials.
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.
- ✗
"Deny" effect with "StringNotEquals" on "aws:SourceIdentity"
Why it's wrong here
SourceIdentity is not a standard condition for authentication.
- ✗
"Deny" effect with "aws:SourceIp" condition
Why it's wrong here
This restricts by IP but does not require IAM credentials.
- ✓
"Deny" effect with "Null" condition on "aws:PrincipalArn"
Why this is correct
Denies access when the principal ARN is null (anonymous requests).
Related concept
Standard ACLs match source addresses.
- ✗
"Allow" effect with "Referer" condition
Why it's wrong here
Referer can be spoofed and does not enforce IAM credentials.
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 SCS-C02 ACL questions on filtering logic and placement.
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Identity and Access Management — study guide chapter
Learn the concepts, then practise the questions
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FAQ
Questions learners often ask
What does this SCS-C02 question test?
Identity and Access Management — This question tests Identity and Access Management — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: "Deny" effect with "Null" condition on "aws:PrincipalArn" — Option C is correct because a bucket policy with a Deny effect and a Null condition on aws:PrincipalArn will block any request that does not have a valid IAM principal ARN (i.e., anonymous requests). This ensures that only requests authenticated with IAM credentials (users/roles) are allowed. Option A uses aws:SourceIdentity which is not relevant for enforcing IAM authentication. Option B uses aws:SourceIp which restricts by IP address but does not enforce IAM credentials. Option D uses aws:Referer which is based on HTTP referer header and does not enforce authentication. To also enforce CloudTrail logging, a separate condition could be added, but the question specifically asks for enforcing IAM credentials.
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.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Last reviewed: Jun 20, 2026
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