Security antipatterns javascript

Security Anti-Patterns Guard for Node.js/TypeScript/Next.js

When to Activate

Activate this skill when generating ANY code involving:

• Node.js backend code
• TypeScript applications
• Next.js (App Router or Pages Router)
• Express/Fastify APIs
• Database queries (Prisma, Drizzle, raw SQL, MongoDB)
• Authentication/authorization logic
• File uploads or user input handling
• API endpoints or Server Actions

Critical Rules (Top 10)

1. NEVER use string concatenation for SQL/NoSQL queries - use parameterized queries or ORM methods
2. NEVER use dangerouslySetInnerHTML with user input without DOMPurify sanitization
3. ALWAYS verify resource ownership (BOLA) - where: { id, userId: session.user.id }
4. ALWAYS validate ALL external input with zod/yup at API boundaries
5. NEVER hardcode secrets - use process.env (not NEXT_PUBLIC_* for secrets)
6. ALWAYS use crypto.randomBytes() or crypto.randomUUID() - never Math.random() for security
7. NEVER trust middleware alone for auth - verify in route handlers (defense in depth)
8. ALWAYS hash passwords with bcrypt/argon2 - never MD5/SHA1/unsalted
9. NEVER use exec() with user input - use execFile() with argument arrays
10. ALWAYS validate file uploads: extension, MIME type, size limits

Module Index

Reference these modules for specific vulnerability patterns:

Module	Covers	OWASP Reference
injection.md	SQL, Command, NoSQL, Template, LDAP injection	A03:2021
xss-output.md	XSS (Reflected, Stored, DOM), output encoding	A03:2021
auth-access.md	BOLA, BFLA, auth, sessions, JWT	API1-3, API5
crypto-secrets.md	Secrets management, encryption, hashing	A02:2021
input-validation.md	Validation, mass assignment, path traversal, uploads	A03:2021, API3
prototype-pollution.md	JS prototype pollution attacks	CWE-1321
typescript-safety.md	Type safety gaps, runtime validation	CWE-843
nextjs-security.md	Middleware bypass, Server Actions, SSRF	CVE-2025-29927, CVE-2025-66478
rsc-security.md	RSC deserialization (React2Shell), DoS, Server Action abuse	CVE-2025-55182, CVE-2025-55184
api-infra.md	Rate limiting, CORS, headers, error handling	API4, API6-7
dependencies.md	Supply chain, slopsquatting, NPM malware, PhantomRaven	A06:2021, CWE-506
nodejs-runtime.md	ReDoS, async hooks exhaustion, HTTP/2 DoS, child processes	CWE-1333, CVE-2025-59466

How to Use This Skill

When generating code:

1. Identify applicable modules based on what you're writing
2. Reference the specific module for detailed BAD/GOOD patterns
3. Apply the GOOD pattern - never generate code matching BAD patterns
4. Verify the output against the Critical Rules above

Quick Reference by Task

Writing...	Reference
Database queries	references/injection.md, references/input-validation.md
API route/endpoint	references/auth-access.md, references/api-infra.md, references/input-validation.md
User authentication	references/auth-access.md, references/crypto-secrets.md
Form handling	references/input-validation.md, references/xss-output.md
File operations	references/input-validation.md, references/nodejs-runtime.md
Next.js Server Actions	references/nextjs-security.md, references/rsc-security.md, references/auth-access.md
React Server Components	references/rsc-security.md, references/nextjs-security.md
Third-party package usage	references/dependencies.md
Rendering user content	references/xss-output.md
Environment/config	references/crypto-secrets.md
Child processes	references/nodejs-runtime.md, references/injection.md

Response Format

When this skill is active, ensure generated code:

1. Includes necessary imports (zod, bcrypt, etc.)
2. Shows the secure pattern being used
3. Includes brief comments explaining security measure if non-obvious
4. Does NOT include insecure alternatives "for reference"