Helmet

Helmet is a series of middlewares for Express/Connect apps that implement various security headers to make your app more secure.

Included middleware

• csp (Content Security Policy)
• hsts (HTTP Strict Transport Security)
• xframe (X-Frame-Options)
• iexss (X-XSS-Protection for IE8+)
• ienoopen (X-Download-Options for IE8+)
• contentTypeOptions (X-Content-Type-Options)
• cacheControl (Cache-Control)
• hidePoweredBy (remove X-Powered-By)

Installation

npm install helmet

Basic usage

var helmet = require('helmet');

To use a particular middleware application-wide, just use it:

app.use(helmet.csp());
app.use(helmet.xframe('deny'));
app.use(helmet.contentTypeOptions());

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

If you just want to use the default-level policies, all you need to do is:

helmet.defaults(app);

Don't want all the defaults?

helmet.defaults(app, { xframe: false });
app.use(helmet.xframe('sameorigin'));

Content Security Policy

The Content Security Policy (W3C Draft) is pretty much required reading if you want to do anything with CSP.

Browser Support

Currently there is CSP support in Firefox and experimental support in Chrome. Both X-Content-Security-Policy and X-WebKit-CSP headers are set by Helmet.

There are two different ways to build CSP policies with Helmet.

Using policy()

policy() eats a JSON blob (including the output of its own toJSON() function) to create a policy. By default helmet has a defaultPolicy that looks like;

Content-Security-Policy: default-src 'self'

To override this and create a new policy you could do something like

policy = {
  defaultPolicy: {
    'default-src': ["'self'"],
    'img-src': ['static.andyet.net','*.cdn.example.com'],
  }
}

helmet.csp.policy(policy);

Using add()

The same thing could be accomplished using add() since the defaultPolicy default-src is already 'self':

helmet.csp.add('img-src', ['static.andyet.net', '*.cdn.example.com']);

Reporting Violations

CSP can report violations back to a specified URL. You can either set the report-uri using policy() or add() or use the reportTo() helper function.

helmet.csp.reportTo('http://example.com/csp');

HTTP Strict Transport Security

draft-ietf-websec-strict-transport-sec-04

This middleware adds the Strict-Transport-Security header to the response.

Basic Usage

To use the default header of Strict-Transport-Security: maxAge=15768000:

helmet.hsts();

To adjust other values for maxAge and to include subdomains:

helmet.hsts(1234567, true);  // hsts(maxAge, includeSubdomains)

X-FRAME-OPTIONS

xFrame is a lot more straight forward than CSP. It has three modes. DENY, SAMEORIGIN, ALLOW-FROM. If your app does not need to be framed (and most don't) you can use the default DENY.

Browser Support

• IE8+
• Opera 10.50+
• Safari 4+
• Chrome 4.1.249.1042+
• Firefox 3.6.9 (or earlier with NoScript)

Here is an example for both SAMEORIGIN and ALLOW-FROM:

helmet.xframe('sameorigin');

helmet.xframe('allow-from', 'http://example.com');

X-XSS-PROTECTION

The following example sets the X-XSS-PROTECTION: 1; mode=block header:

helmet.iexss();

X-Download-Options

Sets the X-Download-Options header to noopen to prevent IE users from executing downloads in your site's context. For more, see this MSDN blog post.

app.use(helmet.ienoopen())

X-Content-Type-Options

The following example sets the X-Content-Type-Options header to its only and default option, nosniff:

helmet.contentTypeOptions();

Cache-Control

The following example sets the Cache-Control header to no-store, no-cache. This is not configurable at this time.

helmet.cacheControl();

Hide X-Powered-By

This middleware will remove the X-Powered-By header if it is set.

helmet.hidePoweredBy()

Note: if you're using Express, you can skip Helmet's middleware if you want:

app.disable('x-powered-by')

To Be Implemented

• Warn when self, unsafe-inline or unsafe-eval are not single quoted
• Warn when unsafe-inline or unsafe-eval are used
• Caching of generated CSP headers
• Device to capture and parse reported CSP violations