The correct answer is that an explicit deny statement in a separate policy, such as a service control policy (SCP) or a permissions boundary, is overriding the allow. This occurs because AWS IAM policy evaluation logic dictates that any explicit deny, regardless of where it is applied, takes precedence over any allow—a principle known as "explicit deny overrides allow." Even if a user has a broad IAM policy granting s3:* on all resources, a deny in an SCP at the organizational level or a permissions boundary attached to the user or role will block access to the specific bucket. On the AWS Certified Security Specialty SCS-C02 exam, this concept frequently appears in troubleshooting scenarios where a seemingly permissive policy still results in a denial, testing your understanding of how SCPs, resource-based policies, and permissions boundaries interact. A common trap is assuming the user’s own allow policy is sufficient, but the key is remembering that explicit denies from any policy layer are absolute. Memory tip: "Deny always wins—think of it as a veto power that no allow can override."
SCS-C02 Identity and Access Management Practice Question
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 security engineer is troubleshooting an issue where an IAM policy allows access to S3 but the user is denied access to a specific bucket. The policy has the following statement:
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 policy statement is too broad and AWS automatically denies access to specific buckets.
Why wrong: Broad allows are permitted; there is no automatic denial.
B
An explicit deny statement in a different policy (e.g., SCP, permissions boundary) is overriding the allow.
Explicit denies take precedence over allows.
C
The S3 bucket has a bucket policy that denies access to the user.
Why wrong: A bucket policy could deny access, but the question asks for the most likely cause given the allow policy; however, an explicit deny in a different policy is more likely.
D
The policy is attached to the user but the user is assuming a role that does not have S3 permissions.
Why wrong: The user's permissions are based on their own policies, not the role.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
An explicit deny statement in a different policy (e.g., SCP, permissions boundary) is overriding the allow.
Option A is correct because an explicit deny in a separate policy, such as a service control policy (SCP) or a permissions boundary, overrides any allow. Option B is wrong because the user's own policy is an allow. Option C is wrong because S3 bucket policies are resource-based and can deny access. Option D is wrong because IAM policies are evaluated as a whole; there is no implicit deny for specific buckets unless a deny exists.
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 policy statement is too broad and AWS automatically denies access to specific buckets.
Why it's wrong here
Broad allows are permitted; there is no automatic denial.
✓
An explicit deny statement in a different policy (e.g., SCP, permissions boundary) is overriding the allow.
Why this is correct
Explicit denies take precedence over allows.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The S3 bucket has a bucket policy that denies access to the user.
Why it's wrong here
A bucket policy could deny access, but the question asks for the most likely cause given the allow policy; however, an explicit deny in a different policy is more likely.
✗
The policy is attached to the user but the user is assuming a role that does not have S3 permissions.
Why it's wrong here
The user's permissions are based on their own policies, not the role.
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.
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: An explicit deny statement in a different policy (e.g., SCP, permissions boundary) is overriding the allow. — Option A is correct because an explicit deny in a separate policy, such as a service control policy (SCP) or a permissions boundary, overrides any allow. Option B is wrong because the user's own policy is an allow. Option C is wrong because S3 bucket policies are resource-based and can deny access. Option D is wrong because IAM policies are evaluated as a whole; there is no implicit deny for specific buckets unless a deny exists.
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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