Content Security Policy middleware

Content Security Policy helps prevent unwanted content being injected into your webpages; this can mitigate XSS vulnerabilities, unintended frames, malicious frames, and more. If you want to learn how CSP works, check out the fantastic HTML5 Rocks guide, the Content Security Policy Reference, and the Content Security Policy specification.

Usage:

var csp = require('helmet-csp');

app.use(csp({
  defaultSrc: ["'self'", 'default.com'],
  scriptSrc: ['scripts.com'],
  styleSrc: ['style.com'],
  imgSrc: ['img.com'],
  connectSrc: ['connect.com'],
  fontSrc: ['font.com'],
  objectSrc: ['object.com'],
  mediaSrc: ['media.com'],
  frameSrc: ['frame.com'],
  sandbox: ['allow-forms', 'allow-scripts'],
  reportUri: '/report-violation', reportOnly: false, // set to true if you only want to report errors setAllHeaders: false, // set to true if you want to set all headers disableAndroid: false, // set to true to disable CSP on Android (can be flaky) safari5: false // set to true if you want to force buggy CSP in Safari 5
}));

You can specify keys in a camel-cased fashion (imgSrc) or dashed (img-src); they are equivalent.

There are a lot of inconsistencies in how browsers implement CSP. Helmet sniffs the user-agent of the browser and sets the appropriate header and value for that browser. If no user-agent is matched, it will set all the headers with the 1.0 spec.

Handling CSP violations

If you've specified a reportUri, browsers will POST any CSP violations to your server. Here's a simple example of a route that handles those reports:

// You need a JSON parser first.
app.use(bodyParser.json());

app.post('/report-violation', function (req, res) {
  if (req.body) {
    console.log('CSP Violation: ', req.body);
  } else {
    console.log('CSP Violation: No data received!');
  }
  res.status(204).end();
});

Not all browsers send CSP violations the same.

Note: If you're using a CSRF module like csurf, you might have problems posting without a valid CSRF token. The fix is to simply put your CSP report route above csurf middleware.

jameswomack/helmet-csp-restify

Content Security Policy middleware

Handling CSP violations