helmet

What is helmet?

Helmet is a middleware for Express applications that helps secure your apps by setting various HTTP headers. It's not a silver bullet, but it can help prevent some well-known web vulnerabilities by setting headers appropriately.

What are helmet's main functionalities?

Content Security Policy

Sets the Content-Security-Policy header to help prevent cross-site scripting attacks and other cross-site injections.

app.use(helmet.contentSecurityPolicy({
  directives: {
    defaultSrc: ["'self'"],
    scriptSrc: ["'self'", "https://trustedscripts.example.com"],
    objectSrc: ["'none'"],
    upgradeInsecureRequests: [],
  }
}));

X-DNS-Prefetch-Control

Controls browser DNS prefetching, which can improve user privacy at the expense of performance.

app.use(helmet.dnsPrefetchControl({ allow: false }));

Expect-CT

Sets the Expect-CT header which allows sites to opt in to reporting and/or enforcement of Certificate Transparency requirements.

app.use(helmet.expectCt({
  enforce: true,
  maxAge: 86400
}));

X-Frame-Options

Sets the X-Frame-Options header to control whether the browser should be allowed to render a page in a <frame>, <iframe>, <embed>, or <object>.

app.use(helmet.frameguard({ action: 'deny' }));

X-Powered-By

Removes the X-Powered-By header to make it slightly harder for attackers to see what potentially vulnerable technology powers your site.

app.use(helmet.hidePoweredBy());

Strict-Transport-Security

Sets the Strict-Transport-Security header to enforce secure (HTTP over SSL/TLS) connections to the server.

app.use(helmet.hsts({
  maxAge: 15552000,
  includeSubDomains: true
}));

X-Download-Options

Sets X-Download-Options for IE8+ to prevent others from embedding your site in an iframe.

app.use(helmet.ieNoOpen());

X-Content-Type-Options

Sets the X-Content-Type-Options header to prevent browsers from MIME-sniffing a response away from the declared content-type.

app.use(helmet.noSniff());

Referrer Policy

Sets the Referrer-Policy header to control what information is sent along with the requests.

app.use(helmet.referrerPolicy({ policy: 'no-referrer' }));

X-XSS-Protection

Sets the X-XSS-Protection header to enable the Cross-site scripting (XSS) filter in most recent web browsers.

app.use(helmet.xssFilter());

Other packages similar to helmet

lusca

Lusca is another security middleware for Express applications that offers a variety of security features such as CSRF protection, CSP, X-Frame options, and more. It is similar to Helmet but allows for more granular configuration of security policies.

cors

CORS is a package for providing a Connect/Express middleware that can be used to enable CORS (Cross-Origin Resource Sharing) with various options. While Helmet focuses on securing your app from various web vulnerabilities, CORS specifically provides middleware to enable CORS and manage cross-origin requests.

README

Helmet

Helmet helps you secure your Express apps by setting various HTTP headers. It's not a silver bullet, but it can help!

Looking for a version of Helmet that supports the Koa framework?

Quick start

First, run npm install helmet --save for your app. Then, in an Express (or Connect) app:

const express = require("express");
const helmet = require("helmet");

const app = express();

app.use(helmet());

// ...

It's best to use Helmet early in your middleware stack so that its headers are sure to be set.

You can also use its pieces individually:

app.use(helmet.xssFilter());
app.use(helmet.frameguard());

You can disable a middleware that's normally enabled by default. This will disable frameguard but include the other defaults.

app.use(
  helmet({
    frameguard: false,
  })
);

You can also set options for a middleware. Setting options like this will always include the middleware, whether or not it's a default.

app.use(
  helmet({
    frameguard: {
      action: "deny",
    },
  })
);

If you're using Express 3, make sure these middlewares are listed before app.router.

How it works

Helmet is a collection of 11 smaller middleware functions that set HTTP response headers. Running app.use(helmet()) will not include all of these middleware functions by default.

Module	Default?
contentSecurityPolicy for setting Content Security Policy
crossdomain for handling Adobe products' crossdomain requests
dnsPrefetchControl controls browser DNS prefetching	✓
expectCt for handling Certificate Transparency
frameguard to prevent clickjacking	✓
hidePoweredBy to remove the X-Powered-By header	✓
hsts for HTTP Strict Transport Security	✓
ieNoOpen sets X-Download-Options for IE8+	✓
noSniff to keep clients from sniffing the MIME type	✓
referrerPolicy to hide the Referer header
xssFilter adds some small XSS protections	✓

You can see more in the documentation.

Changelog

3.23.3 - 2020-06-26

Changed

• helmet.expectCt is no longer a separate package. This should have no effect on end users.
• helmet.frameguard is no longer a separate package. This should have no effect on end users.