This CCSP practice question tests your understanding of cloud application 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 serverless architecture with AWS Lambda to process user-uploaded files. The Lambda function is triggered by an S3 bucket event. While reviewing security, the architect wants to ensure that the Lambda function cannot be invoked by unauthorized S3 buckets or accounts. What is the most secure configuration?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure the Lambda function's resource-based policy to grant permission only to the specific S3 bucket ARN and its owner account.
Option C is correct because the most secure way to restrict Lambda invocation to a specific S3 bucket is to use a resource-based policy that explicitly grants the `lambda:InvokeFunction` permission only to the trusted bucket's ARN and the owning AWS account. This ensures that even if another S3 bucket or account attempts to trigger the function, the invocation is denied by the Lambda permission model, which evaluates both the resource-based policy and the caller's identity.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Use a condition in the policy that checks the source IP address.
Why it's wrong here
IP condition is not specific to S3 bucket.
✗
Place the Lambda function inside a VPC with a VPC endpoint for S3.
Why it's wrong here
VPC placement affects network access but not invocation permissions.
✓
Configure the Lambda function's resource-based policy to grant permission only to the specific S3 bucket ARN and its owner account.
Why this is correct
Restricts invocation to a known source.
Related concept
Read the scenario before looking for a memorised answer.
✗
Attach a resource-based policy that allows any S3 bucket to invoke the function.
Why it's wrong here
Overly permissive.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse network-level controls (like VPC placement or IP filtering) with identity-based access controls, failing to realize that S3 event notifications invoke Lambda through AWS's internal service-to-service channel, which bypasses network restrictions and requires explicit resource-based policy conditions.
Detailed technical explanation
How to think about this question
Lambda resource-based policies use a statement with `Principal: s3.amazonaws.com` and a `Condition` block with `ArnLike` or `StringEquals` to match the specific source bucket ARN and account ID. This is evaluated at invocation time; if the condition fails, Lambda returns an `AccessDeniedException` before the function code runs. In a real-world scenario, an attacker could create a bucket in their own account and configure an S3 event notification pointing to your Lambda function if the resource policy is too permissive, making the explicit bucket ARN condition critical.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A security analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Cloud Application Security — This question tests Cloud Application Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure the Lambda function's resource-based policy to grant permission only to the specific S3 bucket ARN and its owner account. — Option C is correct because the most secure way to restrict Lambda invocation to a specific S3 bucket is to use a resource-based policy that explicitly grants the `lambda:InvokeFunction` permission only to the trusted bucket's ARN and the owning AWS account. This ensures that even if another S3 bucket or account attempts to trigger the function, the invocation is denied by the Lambda permission model, which evaluates both the resource-based policy and the caller's identity.
What should I do if I get this CCSP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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