Nextjs security

Skill FilippoDeSilva/skills/skills/nextjs/nextjs-security

Skills for my agentic development workflow.

Install

npx -y skills add FilippoDeSilva/skills --skill nextjs-security

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What its author says it does

Copied from the file, not written here

Secure Next.js App Router with middleware auth, Server Action validation, CSP headers, and taint APIs. Use when adding authentication middleware, validating Server Action inputs with Zod, or preventing secret leakage to client bundles.

The file declares its own license as MIT. That is the author’s claim about this one file, and it is not the same thing as the license GitHub reports for the repository, which is listed with the other numbers below.

SKILL.md

2.9 KB, 547 tokens by cl100k_base, as published. Nobody here has run it

Next.js Security

Priority: P0 (CRITICAL)

Workflow: Secure Next.js App

Add auth middleware — Create middleware.ts to verify JWT/session on protected routes.
Validate Server Actions — Parse all inputs with Zod schemas; call await auth() first.
Set security headers — Add CSP, HSTS, X-Frame-Options in middleware response.
Use server-only — Import in modules containing secrets to prevent client bundling.
Taint sensitive objects — Use taintObjectReference to block server objects from reaching client.

Secure Server Action Example

See implementation examples

Implementation Guidelines

Next.js Middleware: Use middleware.ts for edge-side authentication, role-based access control (RBAC), and enforcing Security Headers (e.g., Content-Security-Policy (CSP), X-XSS-Protection).
Server Actions: Always sanitize all inputs from FormData or JSON using Zod. Perform authentication checks (await auth()) inside every action to verify caller.
Data Tainting: Use experimental_taint API (taintObjectReference) to ensure sensitive server objects (e.g., User with passwordHash) never leak into Client Component.
Route Handlers (route.ts): Implement rate limiting to prevent brute-force or DoS attacks. Verify Origin/Referer headers to mitigate CSRF (Cross-Site Request Forgery).
Auth Tokens: strictly use HttpOnly, Secure cookies with SameSite: 'Lax' for session management. Never store tokens in localStorage.
Logic Isolation: use server-only package to prevent backend-specific logic from included in client bundle.
Component Purity: Escape all user-provided content rendered in components. Never use dangerouslySetInnerHTML without sanitizer like DOMPurify.

Anti-Patterns

No leaking DB fields to client: Use DTOs; never pass raw model objects.
No process.env in client bundles: Mark as NEXT_PUBLIC_ only if safe to expose.
No unvalidated Server Action inputs: Always validate with Zod schema.
No auth checks in shared Layouts: Auth in layouts insecure; use Middleware.

References

Secure App Router Patterns

What ships with it: 2 files

3.1 KB alongside SKILL.md

evals/

evals.json2.0 KB

references/

implementation.md1.1 KB

Gives 1 of the 12 instructions most security skills give in 547 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 endpointsin 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 sessionshere, and in 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

Set CSP HSTS and X-Frame-Options headers in middleware
Taint sensitive server objects to block client transmission
Implement rate limiting in route handlers
Verify Origin or Referer headers to mitigate CSRF
Use DTOs to prevent leaking database fields to client

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.