security-review

name	security-review
description	Use this skill when adding authentication, handling user input, working with secrets, creating API endpoints, or implementing payment/sensitive features. Provides a comprehensive OWASP security checklist and patterns.

Security Review Skill

This skill ensures all code follows security best practices and identifies potential vulnerabilities.

When to Activate

• Implementing authentication or authorization
• Handling user input or file uploads
• Creating new API endpoints
• Working with secrets or credentials
• Implementing payment features
• Storing or transmitting sensitive data
• Integrating third-party APIs

Security Checklist

1. Secrets Management

FAIL: NEVER Do This

const apiKey = "sk-proj-xxxxx"  // Hardcoded secret
const dbPassword = "password123" // In source code

PASS: ALWAYS Do This

const apiKey = process.env.OPENAI_API_KEY
const dbUrl = process.env.DATABASE_URL

// Verify secrets exist
if (!apiKey) {
  throw new Error('OPENAI_API_KEY not configured')
}

Verification Steps

• No hardcoded API keys, tokens, or passwords
• All secrets in environment variables
• .env.local in .gitignore
• No secrets in git history
• Production secrets in hosting platform (Vercel, Railway)

2. Input Validation

Always Validate User Input

import { z } from 'zod'

// Define validation schema
const CreateUserSchema = z.object({
  email: z.string().email(),
  name: z.string().min(1).max(100),
  age: z.number().int().min(0).max(150)
})

// Validate before processing
export async function createUser(input: unknown) {
  try {
    const validated = CreateUserSchema.parse(input)
    return await db.users.create(validated)
  } catch (error) {
    if (error instanceof z.ZodError) {
      return { success: false, errors: error.issues }
    }
    throw error
  }
}

File Upload Validation

function validateFileUpload(file: File) {
  // Size check (5MB max)
  const maxSize = 5 * 1024 * 1024
  if (file.size > maxSize) {
    throw new Error('File too large (max 5MB)')
  }

  // Type check
  const allowedTypes = ['image/jpeg', 'image/png', 'image/gif']
  if (!allowedTypes.includes(file.type)) {
    throw new Error('Invalid file type')
  }

  // Extension check
  const allowedExtensions = ['.jpg', '.jpeg', '.png', '.gif']
  const extension = file.name.toLowerCase().match(/\.[^.]+$/)?.[0]
  if (!extension || !allowedExtensions.includes(extension)) {
    throw new Error('Invalid file extension')
  }

  return true
}

Verification Steps

• All user inputs validated with schemas
• File uploads restricted (size, type, extension)
• No direct use of user input in queries
• Whitelist validation (not blacklist)
• Error messages don't leak sensitive info

3. SQL Injection Prevention

FAIL: NEVER Concatenate SQL

// DANGEROUS - SQL Injection vulnerability
const query = `SELECT * FROM users WHERE email = '${userEmail}'`
await db.query(query)

PASS: ALWAYS Use Parameterized Queries

// Safe - parameterized query (placeholders, not string interpolation)
await db.query(
  'SELECT * FROM users WHERE email = $1',
  [userEmail]
)

// Or via an ORM / query builder that parameterizes by default
const user = await db.users.findUnique({
  where: { email: userEmail }
})

Verification Steps

• All database queries use parameterized queries
• No string concatenation in SQL
• ORM/query builder used correctly
• Query inputs properly sanitized/parameterized

4. Authentication & Authorization

JWT Token Handling

// FAIL: WRONG: localStorage (vulnerable to XSS)
localStorage.setItem('token', token)

// PASS: CORRECT: httpOnly cookies
res.setHeader('Set-Cookie',
  `token=${token}; HttpOnly; Secure; SameSite=Strict; Max-Age=3600`)

Authorization Checks

export async function deleteUser(userId: string, requesterId: string) {
  // ALWAYS verify authorization first
  const requester = await db.users.findUnique({
    where: { id: requesterId }
  })

  if (requester.role !== 'admin') {
    return NextResponse.json(
      { error: 'Unauthorized' },
      { status: 403 }
    )
  }

  // Proceed with deletion
  await db.users.delete({ where: { id: userId } })
}

Row-Level / Tenant Authorization

Enforce per-row / per-tenant access control in the database or query layer so a user can never read or mutate another user's (or tenant's) rows — even if an application-layer check is missed. This can be done with database row-level security policies, or by always scoping queries to the authenticated user/tenant id in your data-access layer.

-- example (Postgres RLS; adapt to your DB)
-- Enable row-level security on the table
ALTER TABLE users ENABLE ROW LEVEL SECURITY;

-- Users can only view their own data
CREATE POLICY "Users view own data"
  ON users FOR SELECT
  USING (current_user_id() = id);

-- Users can only update their own data
CREATE POLICY "Users update own data"
  ON users FOR UPDATE
  USING (current_user_id() = id);

Verification Steps

• Tokens stored in httpOnly cookies (not localStorage)
• Authorization checks before sensitive operations
• Row-level/tenant authorization enforced
• Role-based access control implemented
• Session management secure

5. XSS Prevention

Sanitize HTML

import DOMPurify from 'isomorphic-dompurify'

// ALWAYS sanitize user-provided HTML
function renderUserContent(html: string) {
  const clean = DOMPurify.sanitize(html, {
    ALLOWED_TAGS: ['b', 'i', 'em', 'strong', 'p'],
    ALLOWED_ATTR: []
  })
  return <div dangerouslySetInnerHTML={{ __html: clean }} />
}

Content Security Policy

Start strict and loosen only with a documented removal plan. Do not default to 'unsafe-inline' or 'unsafe-eval'; they neutralize much of CSP's protection and should be treated as temporary compatibility debt.

// next.config.js
const securityHeaders = [
  {
    key: 'Content-Security-Policy',
    value: `
      default-src 'self';
      base-uri 'self';
      object-src 'none';
      frame-ancestors 'none';
      script-src 'self';
      style-src 'self';
      img-src 'self' data: https:;
      font-src 'self';
      connect-src 'self' https://api.example.com;
    `.replace(/\s{2,}/g, ' ').trim()
  }
]

Verification Steps

• User-provided HTML sanitized
• CSP headers configured
• No unvalidated dynamic content rendering
• React's built-in XSS protection used

6. CSRF Protection

CSRF Tokens

import { csrf } from '@/lib/csrf'

export async function POST(request: Request) {
  const token = request.headers.get('X-CSRF-Token')

  if (!csrf.verify(token)) {
    return NextResponse.json(
      { error: 'Invalid CSRF token' },
      { status: 403 }
    )
  }

  // Process request
}

SameSite Cookies

res.setHeader('Set-Cookie',
  `session=${sessionId}; HttpOnly; Secure; SameSite=Strict`)

Verification Steps

• CSRF tokens on state-changing operations
• SameSite=Strict on all cookies
• Double-submit cookie pattern implemented

7. Rate Limiting

API Rate Limiting

import rateLimit from 'express-rate-limit'

const limiter = rateLimit({
  windowMs: 15 * 60 * 1000, // 15 minutes
  max: 100, // 100 requests per window
  message: 'Too many requests'
})

// Apply to routes
app.use('/api/', limiter)

Expensive Operations

// Aggressive rate limiting for searches
const searchLimiter = rateLimit({
  windowMs: 60 * 1000, // 1 minute
  max: 10, // 10 requests per minute
  message: 'Too many search requests'
})

app.use('/api/search', searchLimiter)

Verification Steps

• Rate limiting on all API endpoints
• Stricter limits on expensive operations
• IP-based rate limiting
• User-based rate limiting (authenticated)

8. Sensitive Data Exposure

Logging

// FAIL: WRONG: Logging sensitive data
console.log('User login:', { email, password })
console.log('Payment:', { cardNumber, cvv })

// PASS: CORRECT: Redact sensitive data
console.log('User login:', { email, userId })
console.log('Payment:', { last4: card.last4, userId })

Error Messages

// FAIL: WRONG: Exposing internal details
catch (error) {
  return NextResponse.json(
    { error: error.message, stack: error.stack },
    { status: 500 }
  )
}

// PASS: CORRECT: Generic error messages
catch (error) {
  console.error('Internal error:', error)
  return NextResponse.json(
    { error: 'An error occurred. Please try again.' },
    { status: 500 }
  )
}

Verification Steps

• No passwords, tokens, or secrets in logs
• Error messages generic for users
• Detailed errors only in server logs
• No stack traces exposed to users

9. Signature Verification

Never trust a payload just because it arrived — verify its signature before acting on it. This applies to inbound webhooks, signed API requests, and any token or message whose authenticity matters. Use your platform's stdlib crypto and always compare digests with a constant-time function.

HMAC Webhook Signature Verification

import crypto from 'node:crypto'

function verifyWebhookSignature(
  rawBody: string,        // the exact raw request body
  signatureHeader: string, // signature the sender provided
  secret: string          // shared secret from your provider's dashboard
): boolean {
  const expected = crypto
    .createHmac('sha256', secret)
    .update(rawBody, 'utf8')
    .digest('hex')

  const a = Buffer.from(expected)
  const b = Buffer.from(signatureHeader)

  // Constant-time compare to avoid timing attacks;
  // length check guards timingSafeEqual's equal-length requirement.
  return a.length === b.length && crypto.timingSafeEqual(a, b)
}

Verifying a Signed Payload / Ownership

// Verify a cryptographic signature over a message before trusting its claim.
// Works for asymmetric signatures (e.g. verifying a public key signed a nonce).
function verifySignedPayload(
  message: string,
  signature: string, // base64-encoded
  publicKeyPem: string
): boolean {
  try {
    const verifier = crypto.createVerify('SHA256')
    verifier.update(message)
    verifier.end()
    return verifier.verify(publicKeyPem, signature, 'base64')
  } catch {
    return false
  }
}

Verification Steps

• Signatures verified on signed requests/webhooks before processing
• Verification uses the exact raw payload (no re-serialization)
• Constant-time comparison used for signature/digest checks
• Never trust ownership or authenticity claims without verifying the signature

10. Dependency Security

Regular Updates

# Check for vulnerabilities
npm audit

# Fix automatically fixable issues
npm audit fix

# Update dependencies
npm update

# Check for outdated packages
npm outdated

Lock Files

# ALWAYS commit lock files
git add package-lock.json

# Use in CI/CD for reproducible builds
npm ci  # Instead of npm install

Verification Steps

• Dependencies up to date
• No known vulnerabilities (npm audit clean)
• Lock files committed
• Dependabot enabled on GitHub
• Regular security updates

Security Testing

Automated Security Tests

// Test authentication
test('requires authentication', async () => {
  const response = await fetch('/api/protected')
  expect(response.status).toBe(401)
})

// Test authorization
test('requires admin role', async () => {
  const response = await fetch('/api/admin', {
    headers: { Authorization: `Bearer ${userToken}` }
  })
  expect(response.status).toBe(403)
})

// Test input validation
test('rejects invalid input', async () => {
  const response = await fetch('/api/users', {
    method: 'POST',
    body: JSON.stringify({ email: 'not-an-email' })
  })
  expect(response.status).toBe(400)
})

// Test rate limiting
test('enforces rate limits', async () => {
  const requests = Array(101).fill(null).map(() =>
    fetch('/api/endpoint')
  )

  const responses = await Promise.all(requests)
  const tooManyRequests = responses.filter(r => r.status === 429)

  expect(tooManyRequests.length).toBeGreaterThan(0)
})

Pre-Deployment Security Checklist

Before ANY production deployment:

• Secrets: No hardcoded secrets, all in env vars
• Input Validation: All user inputs validated
• SQL Injection: All queries parameterized
• XSS: User content sanitized
• CSRF: Protection enabled
• Authentication: Proper token handling
• Authorization: Role checks in place
• Rate Limiting: Enabled on all endpoints
• HTTPS: Enforced in production
• Security Headers: CSP, X-Frame-Options configured
• Error Handling: No sensitive data in errors
• Logging: No sensitive data logged
• Dependencies: Up to date, no vulnerabilities
• Row-Level/Tenant Authorization: Enforced in DB or query layer
• CORS: Properly configured
• File Uploads: Validated (size, type)
• Signatures: Verified on signed requests/webhooks (if applicable)

Resources

• OWASP Top 10
• OWASP Cheat Sheet Series
• Next.js Security
• Web Security Academy

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Remember: Security is not optional. One vulnerability can compromise the entire platform. When in doubt, err on the side of caution.