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Question 124 of 1,748

Identity and Access Management →mediumMultiple ChoiceObjective-mapped

S3 Bucket Policy Explicit Deny Overrides IAM Role Allow

This SCS-C02 practice question tests your understanding of identity and access management. 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 has an S3 bucket with a bucket policy that grants access to an IAM role used by an application running on EC2. The application is unable to read objects from the bucket, even though the IAM role has the necessary permissions. 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.

A
The bucket is in a different AWS account.
Why wrong: Cross-account access is possible with proper policies.
B
The bucket policy denies access to the IAM role.
A deny in bucket policy overrides any allow.
C
The bucket policy does not explicitly allow the IAM role.
Why wrong: If role has permissions, bucket policy must also allow.
D
The IAM role has an explicit deny statement.
Why wrong: If the role had explicit deny, it would be a cause, but the question says role has necessary permissions.

Full breakdown with real-world context →

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

✓

The bucket policy denies access to the IAM role.

Option B is correct because the most likely cause is that the bucket policy explicitly denies access to the IAM role. Even though the IAM role has the necessary permissions via its attached policies, an explicit deny in the bucket policy overrides any allow, resulting in denied access. Option A is incorrect because cross-account access can be granted with proper permissions. Option C is incorrect because while a missing explicit allow would also deny access by default, the question says the IAM role has the necessary permissions, implying the issue is an explicit deny. Option D is incorrect because if the IAM role had an explicit deny, it would also deny access, but the role is stated to have the necessary permissions.

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 is in a different AWS account.
Why it's wrong here
Cross-account access is possible with proper policies.
✓
The bucket policy denies access to the IAM role.
Why this is correct
A deny in bucket policy overrides any allow.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The bucket policy does not explicitly allow the IAM role.
Why it's wrong here
If role has permissions, bucket policy must also allow.
✗
The IAM role has an explicit deny statement.
Why it's wrong here
If the role had explicit deny, it would be a cause, but the question says role has necessary permissions.

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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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: The bucket policy denies access to the IAM role. — Option B is correct because the most likely cause is that the bucket policy explicitly denies access to the IAM role. Even though the IAM role has the necessary permissions via its attached policies, an explicit deny in the bucket policy overrides any allow, resulting in denied access. Option A is incorrect because cross-account access can be granted with proper permissions. Option C is incorrect because while a missing explicit allow would also deny access by default, the question says the IAM role has the necessary permissions, implying the issue is an explicit deny. Option D is incorrect because if the IAM role had an explicit deny, it would also deny access, but the role is stated to have the necessary permissions.

What should I do if I get this SCS-C02 question wrong?

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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