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How to Find AWS Lambda Functions with Public Resource-Based Policies

Publicly accessible services could expose sensitive data to bad actors.

info

This security check is part of the CIS Amazon Web Services Benchmarks and is rated severity low.

Prerequisites​

This guide assumes that you have already installed and configured Fix Inventory to collect your AWS resources.

Directions​

  1. Execute the following search command in Fix Inventory Shell:

    > search is(aws_lambda_function) and function_policy.statement[*].{principal~"*" or principal.AWS~"*" or principal.CanonicalUser~"*"}
    ​kind=aws_lambda_function, ..., region=fixinventory-poweruser
    ​kind=aws_lambda_function, ..., account=poweruser-team

  2. Pipe the search command into the dump command:

    > search is(aws_lambda_function) and function_policy.statement[*].{principal~"*" or principal.AWS~"*" or principal.CanonicalUser~"*"} | dump
    ​reported:
    ​  id: /aws/lambda/123
    ​  name: some-name
    ​  ctime: '2022-12-05T22:53:14Z'
    ​  kind: aws_lambda_function
    ​  age: 2mo28d

    The command output will list the details of all non-compliant aws_lambda_function resources.

Remediation​

  • Grant usage permission on a per-resource basis and applying least privilege principle.
note

Please refer to the AWS Lambda documentation for details.

Further Reading​