The answer is to add a condition using aws:SourceAccount with the company’s own account ID, as this is the most effective way to restrict S3 cross-account access. The aws:SourceAccount condition key explicitly checks the AWS account ID of the requester, overriding any conflicting aws:SourceArn condition that might reference an external account. This ensures that only requests originating from the company’s account are permitted, regardless of the ARN specified. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of how to secure S3 bucket policies against unintended cross-account access, a common trap being reliance on aws:SourceArn alone, which can be bypassed if the ARN belongs to another account. A key memory tip is to think of aws:SourceAccount as the “account gatekeeper” that overrides any ARN-based permissions, making it the definitive condition for restricting access to a single account.
SCS-C02 Management and Security Governance Practice Question
This SCS-C02 practice question tests your understanding of management and security governance. 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 notices that an S3 bucket contains objects that are accessible to authenticated users from other AWS accounts. The bucket policy allows access to the 'aws:SourceArn' condition that references an Amazon Resource Name (ARN) from another account. What is the MOST effective way to restrict access to only users from the company's own account?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a condition using 'aws:SourceAccount' with the company's account ID.
Option D is correct because using 'aws:SourceAccount' condition with the company's account ID ensures only requests originating from that account are allowed. Option A is incorrect because removing the bucket policy does not address existing objects. Option B is incorrect because SCPs do not affect cross-account access to resources. Option C is incorrect because 'aws:SourceArn' is already used; the issue is the ARN belongs to another account.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Apply an SCP to deny s3:GetObject for any principal outside the organization.
Why it's wrong here
SCPs apply to principals within the organization, not to external principals.
✗
Remove the bucket policy and add an IAM policy to the company's users.
Why it's wrong here
Does not restrict access to existing objects that are already shared.
✗
Modify the condition to use 'aws:SourceArn' with an ARN from the company's account.
Why it's wrong here
Does not prevent other accounts from using a different source ARN.
✓
Add a condition using 'aws:SourceAccount' with the company's account ID.
Why this is correct
Restricts access to requests originating from the specified account.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SCS-C02 NAT questions on configuration and troubleshooting.
Management and Security Governance — This question tests Management and Security Governance — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Add a condition using 'aws:SourceAccount' with the company's account ID. — Option D is correct because using 'aws:SourceAccount' condition with the company's account ID ensures only requests originating from that account are allowed. Option A is incorrect because removing the bucket policy does not address existing objects. Option B is incorrect because SCPs do not affect cross-account access to resources. Option C is incorrect because 'aws:SourceArn' is already used; the issue is the ARN belongs to another account.
What should I do if I get this SCS-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SCS-C02 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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