DEA-C01 Data Security and Governance Practice Question
A data engineer needs to share a dataset from an S3 bucket in Account A with users in Account B. The dataset must remain encrypted at rest with an S3-managed key. What is the MOST secure way to grant cross-account access?
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
✓
Create a bucket policy that grants cross-account access to an IAM role in Account B.
A bucket policy granting access to the IAM role in Account B is the recommended secure method for cross-account access to S3 objects encrypted with S3-managed keys. Option A is insecure because it grants public access. Option C is incorrect because ACLs are legacy and less secure for cross-account scenarios. Option D is incorrect because while S3 VPC endpoints are a valid AWS feature that provides private connectivity to S3, they do not grant cross-account access; bucket policies are still required to authorize access.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Make the bucket public and use bucket policies to allow only Account B users.
Why it's wrong here
A public bucket exposes objects to anonymous principals, and a bucket policy restricting to Account B cannot undo that exposure; SSE-S3 also leaves the bucket ACL as the access boundary. Bucket policies granting a specific Account B principal are the correct mechanism when the bucket stays private.
- ✓
Create a bucket policy that grants cross-account access to an IAM role in Account B.
Why this is correct
A bucket policy granting access to an IAM role in Account B satisfies the cross-account requirement without exposing long-lived credentials. Account B users assume that role via AWS STS, receiving temporary credentials scoped by the trust policy. SSE-S3 encryption remains intact, since S3-managed keys need no cross-account KMS permissions, unlike SSE-KMS.
- ✗
Use S3 object ACLs to grant access to Account B's root user.
Why it's wrong here
Object ACLs cannot grant access to another account's root user as a delegation mechanism and are disabled by S3 Object Ownership settings; bucket policies with explicit principals are the supported route. ACLs are tempting for legacy per-object grants, which suit same-account sharing.
- ✗
Use an S3 VPC endpoint to allow Account B users through private IPs.
Why it's wrong here
A VPC endpoint only changes the network path for clients already authorised by IAM or bucket policy; it grants no cross-account permissions. It is tempting because private connectivity appears secure, but it is correct for restricting traffic to a VPC, not for sharing data between accounts.
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 |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DEA-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DEA-C01 exam.