Rule Details

This rule detects Express.js applications that are missing the helmet middleware. Helmet sets various HTTP headers to help protect your app from well-known web vulnerabilities.

Missing security headers can expose your application to:

Clickjacking attacks (X-Frame-Options)
XSS attacks (X-XSS-Protection, Content-Security-Policy)
MIME-type sniffing attacks (X-Content-Type-Options)
Man-in-the-middle attacks (Strict-Transport-Security)

Examples

❌ Incorrect

import express from 'express';
const app = express();

// Missing helmet middleware - VULNERABLE
app.get('/', (req, res) => res.send('Hello'));

app.listen(3000);

✅ Correct

import express from 'express';
import helmet from 'helmet';

const app = express();

// Helmet adds security headers
app.use(helmet());

app.get('/', (req, res) => res.send('Hello'));

app.listen(3000);

Options

Option	Type	Default	Description
`allowInTests`	`boolean`	`false`	Allow missing helmet in test files
`alternativeMiddleware`	`string[]`	`[]`	Alternative security headers middleware names to accept

{
  "rules": {
    "express-security/require-helmet": [
      "error",
      {
        "allowInTests": true,
        "alternativeMiddleware": ["securityHeaders"]
      }
    ]
  }
}

When Not To Use It

Never disable this rule in production. Security headers are a fundamental protection layer.

Known False Negatives

The following patterns are not detected due to static analysis limitations:

App Instance from Variable

Why: Express app stored in variable may not be recognized.

// ❌ NOT DETECTED - App from factory function
const app = createExpressApp();
// Helmet might be applied in createExpressApp, or not

Mitigation: Apply rule to factory modules. Document helmet usage centrally.

Conditional Middleware

Why: Middleware applied inside conditions is not tracked.

// ❌ NOT DETECTED - Conditional helmet
if (process.env.NODE_ENV === 'production') {
  app.use(helmet());
}
// Development may run without headers

Mitigation: Always apply helmet unconditionally. Use environment-specific configuration inside helmet options.

Framework Wrappers

Why: Higher-level frameworks may include helmet internally.

// ❌ FALSE POSITIVE RISK - Framework includes helmet
import { createServer } from '@my-company/express-framework';
const app = createServer(); // May include helmet

Mitigation: Configure alternativeMiddleware option. Add framework-specific patterns.

Late Middleware Application

Why: Helmet applied after route definitions is less effective.

// ❌ NOT DETECTED - Helmet AFTER routes
app.get('/api', handler);
app.use(helmet()); // Security headers won't apply to /api

Mitigation: Ensure helmet is among the first middleware. Review middleware order in code review.

Custom Security Headers

Why: Manual header setting without helmet is not recognized.

// ❌ NOT DETECTED - Manual headers instead of helmet
app.use((req, res, next) => {
  res.setHeader('X-Frame-Options', 'DENY');
  res.setHeader('X-Content-Type-Options', 'nosniff');
  next();
});

Mitigation: Use helmet for comprehensive coverage. Configure alternativeMiddleware for known patterns.

require-helmet