Mern sec

Skill edfenton/claude-skills/mern/mern-sec

A collection of Claude Code skills for iOS, MERN, NEAN, and shared development workflows

Install

npx -y skills add edfenton/claude-skills --skill mern-sec

Assembled from the repository path, not quoted from the project. Check it against their README if it does not work.

One thing to look at

2 stars2 stars. Stars are a popularity signal and not a quality one, but at this level it is likely that nobody has read this closely except its author, and you would be relying on your own review.

What its author says it does

Copied from the file, not written here

Security policy for MERN apps. Enforces OWASP Top 10 and CWE Top 25 mitigations.

SKILL.md

1.2 KB, 239 tokens by cl100k_base, as published. Nobody here has run it

Purpose

Ensure MERN code is secure by default. For security output format and core refusal policy, see /shared-sec-baseline.

MERN-specific security concerns (always check)

NoSQL injection — reject $-prefixed and dot-notation keys from user input
Input validation — schema validation (Zod/Joi) at every API boundary
XSS — React escapes by default; audit dangerouslySetInnerHTML and raw HTML rendering
CSRF — required when using cookie-based auth; use tokens or SameSite=Strict
Auth/authz gaps — verify authorization on every protected route handler, not just frontend
Token storage — avoid localStorage for sensitive tokens without justification; prefer httpOnly cookies

Standard security (brief check)

Error responses: safe envelopes, no stack traces or internal details
Rate limiting: on auth endpoints, expensive operations, public APIs
Dependencies: lockfile committed, no known critical vulnerabilities

Reference

For detailed OWASP/CWE mitigation patterns, see reference/mern-sec-reference.md

What ships with it: 1 file

6.0 KB alongside SKILL.md

reference/

mern-sec-reference.md6.0 KB

Gives 1 of the 12 instructions most security skills give in 239 tokens

Counted across 648 of the 828 authors here whose files we hold, read 2026-08-07

Parameterize all database queriesin 68 of 648, across 51 files
Hash passwords using bcrypt, scrypt, or argon2in 49 of 648, across 36 files
Apply rate limiting to authentication endpointshere, and in 48 of 648, across 24 files
Configure security headersin 35 of 648, across 19 files
Validate all inputsin 32 of 648, across 24 files
Validate all external input at the system boundaryin 29 of 648, across 19 files
Run containers as a non-root userin 28 of 648, across 15 files
Use httponly secure samesite cookies for sessionsin 26 of 648, across 15 files
Run dependency audits before every releasein 21 of 648, across 10 files
Encode output to prevent cross-site scriptingin 21 of 648, across 11 files
Copy dependencies before source codein 20 of 648, across 9 files
Store secrets in environment variablesin 20 of 648, across 18 files

Said here and by no other author read

reject dollar-prefixed keys from user input
apply schema validation at API boundaries
audit dangerouslySetInnerHTML and raw HTML rendering
omit stack traces from error responses
commit dependency lockfiles

Grouped from the skills themselves: near-identical wordings counted once, and counted by distinct author, so one author publishing three of these counts once. Length counted with cl100k_base; the agent that loads this file may tokenize it differently.