A company is building an application on AWS. The application uses multiple AWS Lambda functions to retrieve sensitive data from a single Amazon S3 bucket for processing. The company must ensure that…

Granting full S3 bucket access to all Lambda functions through a shared IAM role violates the principle of least privilege, as it provides excessive permissions beyond what each function might need, increasing the blast radius in case of a security compromise.

Configuring Lambda functions within a VPC and using a bucket policy for VPC endpoint access enhances network security by restricting access to a private endpoint. However, it does not provide granular authorization at the individual Lambda function level, thus failing to enforce the principle of least privilege for specific function access to data.

Creating individual IAM roles for each Lambda function and granting only the necessary, specific permissions to the S3 bucket for each role is the most effective way to implement the principle of least privilege. This ensures that each function has the minimal required access to sensitive data, preventing over-privilege and improving security.

While a bucket policy can grant access based on Lambda function ARNs, using IAM roles is the standard and recommended practice for assigning permissions to AWS services like Lambda. IAM roles offer a clearer and more robust mechanism for managing execution permissions and auditing compared to embedding function-specific permissions directly in a bucket policy for multiple functions.