The answer is to add a bucket policy statement that denies all access unless the request comes from a specific IP address that does not exist. This works because AWS IAM policies evaluate explicit denies before any allows, so a deny condition with an impossible source IP—such as 0.0.0.0/32—creates a universal block without deleting the bucket or its existing policy. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of policy evaluation logic and the principle of least privilege during an emergency block S3 bucket access situation. A common trap is choosing to delete the IAM role, which breaks other dependent services, or modifying the bucket policy in a way a compromised role could revert. Remember the memory tip: “Deny with a ghost IP—no one gets in, and the policy stays intact.”
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. 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 security engineer is investigating a potential data exfiltration from an Amazon S3 bucket. The bucket policy allows access to a specific IAM role, but the engineer suspects that the role has been compromised. The engineer wants to quickly block all access to the bucket without deleting the bucket or the policy. What is the BEST course of action?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a bucket policy statement that denies access unless the request comes from a specific IP address that does not exist.
Option C is correct because adding a deny condition with a source IP that doesn't exist effectively blocks all access. Option A is wrong because deleting the role would affect other resources. Option B is wrong because modifying the bucket policy might be reverted if the role has permissions. Option D is wrong because blocking at the network layer does not prevent access from within AWS.
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.
✗
Delete the IAM role that is allowed access to the bucket.
Why it's wrong here
Deleting the role could affect other services that depend on it.
✗
Use AWS WAF to block the IP addresses of the compromised role.
Why it's wrong here
AWS WAF is for web traffic, not S3 access.
✗
Modify the bucket policy to deny all principals.
Why it's wrong here
The compromised role might have iam:PutRolePolicy permissions to revert.
✓
Add a bucket policy statement that denies access unless the request comes from a specific IP address that does not exist.
Why this is correct
A deny condition with an impossible IP address blocks all access effectively.
Clue confirmation
The clue word "best" 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.
Infrastructure Security — This question tests Infrastructure Security — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Add a bucket policy statement that denies access unless the request comes from a specific IP address that does not exist. — Option C is correct because adding a deny condition with a source IP that doesn't exist effectively blocks all access. Option A is wrong because deleting the role would affect other resources. Option B is wrong because modifying the bucket policy might be reverted if the role has permissions. Option D is wrong because blocking at the network layer does not prevent access from within AWS.
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: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Question Discussion
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