One template literal in db.query() is a SQL injection, and one exec() with a request value lets anyone run commands on your server. This skill finds those and nine other security mistakes in Node.js server code (Express, Fastify, Koa, NestJS, plain Node; JavaScript or TypeScript) before you merge or deploy, and tells you how to fix each one.

Your agent runs a scanner on your .js and .ts files. It removes comments, keeps strings, follows a query or command built in a variable (also with +=) to the call that runs it, and knows promisify(exec), mysql2, pg, knex, Prisma raw queries, better-sqlite3 and TypeORM. Placeholders and tagged queries are fine. Browser code and test files are skipped. It never runs Node or installs packages. 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)

• E01: command injection: exec or execSync with a command built from changing values

• E02: SQL built with a template literal or + and passed to query(), execute(), prepare(), $queryRawUnsafe() or whereRaw()

• E03: eval, new Function or the vm module on changing code

• E04: a hardcoded JWT secret, session secret, password or API key

REVIEW (check before release)

• E11: CORS with any origin and credentials (cors, NestJS enableCors, Fastify)

• E12: jwt.decode without verify, the none algorithm, or ignoreExpiration

• E13: TLS certificate checks turned off

• E14: secure or httpOnly false on session cookies

• E15: res.redirect() to a URL from the request

• E16: Math.random() for tokens, codes or salts

• E17: stack traces sent to clients

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 server, and the real report the scanner produces on the risky one

Limits

It reads code as text, not as a full JavaScript parser: values are followed within a file only, and MongoDB injection, ORM escaping and dependencies are not checked. NOT FLAGGED is not a guarantee.

Contents

One ZIP file with 7 files: SKILL.md, the scanner in scripts/ (2 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.