One bucket policy with Principal "*", one security group with port 22 open to 0.0.0.0/0, or one password in the template is enough to lose data or the whole AWS account. This skill finds those and nine other CloudFormation mistakes before you deploy, and tells you how to fix each one.

Your agent runs a scanner on your templates in YAML (with !Ref, !Sub, !GetAtt and !If) and JSON, including SAM and CDK output. It finds each resource by its Type and judges the properties that matter for it, treats intrinsic functions and {{resolve:...}} dynamic references as references, not values, and reports each finding at the property's line. It never calls AWS or deploys anything. It returns BLOCK, REVIEW, or NOT FLAGGED, with the file, line, reason, and a safer approach. Secrets are never printed.

What it checks

BLOCK (fix before shipping)

• C01: S3 buckets that everyone can write to, delete from or list

• C02: SSH, RDP, database or all ports open to 0.0.0.0/0 or ::/0

• C03: passwords, keys and tokens written in the template or parameter defaults

• C04: IAM policies with Action on Resource , or AdministratorAccess

• C05: RDS, Aurora or Redshift with PubliclyAccessible true

REVIEW (check before release)

• C11: RDS, EBS, EFS or Redshift storage without encryption

• C12: S3 buckets that everyone can read

• C13: other ports open to the internet

• C14: secret parameters without NoEcho

• C15: DynamoDB, EFS or RDS data deleted with the stack

• C16: Lambda function URLs or permissions open to anyone

• C17: load balancers or CloudFront serving plain HTTP

What's included

• The scanner (Python 3.9+, standard library only)

• A rules guide with the reason and safer approach for each rule

• A risky and a safe example template, and the real report the scanner produces on the risky one

Limits

It reads each template as written: values passed at deploy time, Conditions, nested stacks, StackSets, account-level Block Public Access and service control policies are not evaluated. NOT FLAGGED is not a guarantee.

Contents

One ZIP file with 8 files: SKILL.md, the scanner in scripts/ (3 Python files), references/rules.md (every rule with its reason and safer approach), and examples/ (2 example files plus report.md, the real scanner output on the risky example).

How to use: This is an agent skill: a folder with a SKILL.md file and Python scripts that an AI coding agent such as Claude Code, Cursor, or Codex CLI can run. Unzip it into your agent's skills folder (for Claude Code: ~/.claude/skills/), then ask your agent to check your project. The scripts also run on their own with Python 3.9 or newer, with nothing to install. They read your files only: no network access, and nothing is sent anywhere.