CCSP Cloud Application Security Practice Question
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?
⚠ Common exam trap
A common mix-up: candidates 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.
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
✓
Configure the Lambda function's resource-based policy to grant permission only to the specific S3 bucket ARN and its owner account.
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.
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.
- ✗
Attach a resource-based policy that allows any S3 bucket to invoke the function.
Why it's wrong here
Overly permissive.
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 |
Go deeper
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CCSP practice question is part of Courseiva's free ISC2 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 CCSP exam.