thesimonho/security-best-practices

Security Best Practices

This skill provides security best practices and identifies potential vulnerabilities.

Security Checklist

1. Secrets Management

❌ NEVER Do This

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

✅ 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.errors };
    }
    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

❌ NEVER Concatenate SQL

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

✅ ALWAYS Use Parameterized Queries

// 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

// ❌ 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

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)

-- 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

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

// 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

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

// ❌ 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

// ❌ 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. Blockchain Security (Solana)

Wallet Verification

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

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 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 checks before transactions
• [ ] No blind transaction signing

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);
});