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

NEVER Do This

typescript

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

ALWAYS Do This

typescript

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

typescript

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.errors }
    }
    throw error
  }
}

File Upload Validation

typescript

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

NEVER Concatenate SQL

typescript

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

ALWAYS Use Parameterized Queries

typescript

// Safe - parameterized query
const { data } = await supabase
  .from('users')
  .select('*')
  .eq('email', userEmail)

// Or with raw SQL
await db.query(
  'SELECT * FROM users WHERE email = $1',
  [userEmail]
)

Verification Steps

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

4. Authentication & Authorization

JWT Token Handling

typescript

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

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

Authorization Checks

typescript

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 Security (Supabase)

sql

-- Enable RLS on all tables
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 (auth.uid() = id);

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

Verification Steps

• Tokens stored in httpOnly cookies (not localStorage)
• Authorization checks before sensitive operations
• Row Level Security enabled in Supabase
• Role-based access control implemented
• Session management secure

5. XSS Prevention

Sanitize HTML

typescript

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

typescript

// next.config.js
const securityHeaders = [
  {
    key: 'Content-Security-Policy',
    value: `
      default-src 'self';
      script-src 'self' 'unsafe-eval' 'unsafe-inline';
      style-src 'self' 'unsafe-inline';
      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

typescript

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

typescript

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

typescript

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

typescript

// 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

typescript

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

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

Error Messages

typescript

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

// 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. Dependency Security

Regular Updates

bash

# Check for vulnerabilities
npm audit

# Fix automatically fixable issues
npm audit fix

# Update dependencies
npm update

# Check for outdated packages
npm outdated

Lock Files

bash

# 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

typescript

// 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:

Resources

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