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

# Security Review Skill

This skill ensures that 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 if 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 set on 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 (max 5MB)
  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 do not leak sensitive information

### 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 see 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
- [ ] Secure session management

### 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 rendering of unvalidated dynamic content
- [ ] React's native XSS protection utilized

### 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 in 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 (authenticated) rate limiting

### 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
- [ ] Generic error messages for users
- [ ] Detailed errors only in server logs
- [ ] No stack traces exposed to users

### 9. Blockchain Security (Solana)

#### Wallet Verification

```typescript
import { verify } from "@solana/web3.js";

async function verifyWalletOwnership(
  publicKey: string,
  signature: string,
  message: string,
) {
  try {
    const isValid = verify(
      Buffer.from(message),
      Buffer.from(signature, "base64"),
      Buffer.from(publicKey, "base64"),
    );
    return isValid;
  } catch (error) {
    return false;
  }
}
```

#### Transaction Verification

```typescript
async function verifyTransaction(transaction: Transaction) {
  // Verify recipient
  if (transaction.to !== expectedRecipient) {
    throw new Error("Invalid recipient");
  }

  // Verify amount
  if (transaction.amount > maxAmount) {
    throw new Error("Amount exceeds limit");
  }

  // Verify if user has sufficient balance
  const balance = await getBalance(transaction.from);
  if (balance < transaction.amount) {
    throw new Error("Insufficient balance");
  }

  return true;
}
```

#### Verification Steps

- [ ] Wallet signatures verified
- [ ] Transaction details validated
- [ ] Balance verification before transactions
- [ ] No blind signing of transactions

### 10. 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 (clean npm audit)
- [ ] 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-Deploy 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 implemented
- [ ] **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**: Updated, no vulnerabilities
- [ ] **Row Level Security**: Enabled on Supabase
- [ ] **CORS**: Correctly configured
- [ ] **File Upload**: Validated (size, type)
- [ ] **Wallet Signatures**: Verified (if blockchain)

## Resources

- [OWASP Top 10](https://owasp.org/www-project-top-ten/)
- [Next.js Security](https://nextjs.org/docs/security)
- [Supabase Security](https://supabase.com/docs/guides/auth)
- [Web Security Academy](https://portswigger.net/web-security)

---

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