This CV0-004 practice question tests your understanding of security. 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 uses a multi-account AWS organization with separate accounts for development, testing, and production. A developer in the development account needs to access an S3 bucket in the production account to retrieve log files for troubleshooting. The developer has an IAM user in the development account with full S3 permissions, and the production account's S3 bucket policy includes a statement that grants access to the root user of the development account. However, when the developer attempts to access the bucket using AWS CLI with their IAM user credentials, they receive an 'Access Denied' error. The security team has verified that there are no explicit deny policies in either account, and that the bucket policy is correctly configured. The administrator has confirmed that the developer's IAM user has permissions to perform S3 operations. Which of the following is the MOST likely cause of the access failure?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The production account must have an IAM role with a trust policy that allows the development account to assume it.
Cross-account S3 access typically requires the developer to assume an IAM role in the production account with a trust policy allowing the development account. The bucket policy granting access to the root user of the development account does not automatically grant access to IAM users in that account; the users must assume the role to get temporary credentials. Adding the user to a group in the target account is not possible across accounts. Using root credentials is insecure. VPC peering addresses network connectivity, not IAM 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 developer's IAM user needs to be added to an IAM group in the production account.
Why it's wrong here
IAM groups cannot contain users from other accounts; cross-account access requires roles.
✓
The production account must have an IAM role with a trust policy that allows the development account to assume it.
Why this is correct
An IAM role with a trust policy enables the developer to assume the role and access the bucket.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
A VPC peering connection must be established between the two accounts.
Why it's wrong here
VPC peering is for network connectivity, not for IAM-based S3 access.
✗
The developer should use the root user credentials of the development account to access the bucket.
Why it's wrong here
Root user credentials are insecure and should not be shared or used for routine tasks.
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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
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 CV0-004 ACL questions on filtering logic and placement.
Security — This question tests Security — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The production account must have an IAM role with a trust policy that allows the development account to assume it. — Cross-account S3 access typically requires the developer to assume an IAM role in the production account with a trust policy allowing the development account. The bucket policy granting access to the root user of the development account does not automatically grant access to IAM users in that account; the users must assume the role to get temporary credentials. Adding the user to a group in the target account is not possible across accounts. Using root credentials is insecure. VPC peering addresses network connectivity, not IAM permissions.
What should I do if I get this CV0-004 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 CV0-004 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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