csurfer

Temporary fork of csurf until split token/generation lands.

Node.js CSRF protection middleware.

Requires either a session middleware or cookie-parser to be initialized first.

• If you are setting the "cookie" option to a non-false value, then you must use cookie-parser before this module.
• Otherwise, you must use a session middleware before this module. For example:
  • express-session
  • cookie-session

If you have questions on how this module is implemented, please read Understanding CSRF.

Installation

$ npm install csurfer

API

var csurf = require('csurfer')

csurf([options])

Create a middleware for CSRF token creation and validation. This middleware adds a req.csrfToken() function to make a token which should be added to requests which mutate state, within a hidden form field, query-string etc. This token is validated against the visitor's session or csrf cookie.

Options

The csurf function takes an optional options object that may contain any of the following keys:

cookie

Determines if the token secret for the user should be stored in a cookie or in req.session. Defaults to false.

When set to true (or an object of options for the cookie), then the module changes behavior and no longer uses req.session. This means you are no longer required to use a session middleware. Instead, you do need to use the cookie-parser middleware in your app before this middleware.

When set to an object, cookie storage of the secret is enabled and the object contains options for this functionality (when set to true, the defaults for the options are used). The options may contain any of the following keys:

• key - the name of the cookie to use to store the token secret (defaults to '_csrf').
• path - the path of the cookie (defaults to '/').
• any other res.cookie option can be set.

ignoreMethods

An array of the methods for which CSRF token checking will disabled. Defaults to ['GET', 'HEAD', 'OPTIONS'].

sessionKey

Determines what property ("key") on req the session object is located. Defaults to 'session' (i.e. looks at req.session). The CSRF secret from this library is stored and read as req[sessionKey].csrfSecret.

If the "cookie" option is not false, then this option does nothing.

value

Provide a function that the middleware will invoke to read the token from the request for validation. The function is called as value(req) and is expected to return the token as a string.

The default value is a function that reads the token from the following locations, in order:

• req.body._csrf - typically generated by the body-parser module.
• req.query._csrf - a built-in from Express.js to read from the URL query string.
• req.headers['csrf-token'] - the CSRF-Token HTTP request header.
• req.headers['xsrf-token'] - the XSRF-Token HTTP request header.
• req.headers['x-csrf-token'] - the X-CSRF-Token HTTP request header.
• req.headers['x-xsrf-token'] - the X-XSRF-Token HTTP request header.

Split Token Generation/Validation

Token generation and verification can be performed in separate steps.

csurf.generator([options])

Create a middleware which adds two functions to the req object: req.csrfToken() for generating a token and req.verifyToken() for validating the token from the request. It takes the same options as the combined csurf middleware.

csurf.validator([options])

Create a middleware which calls req.verifyToken() to perform the token validation. Note that csurf.generator() must be called earlier in the middleware stack so that req.verifyToken() is defined. The only options it takes is ignoreMethods.

Example

Simple express example

The following is an example of some server-side code that generates a form that requires a CSRF token to post back.

var cookieParser = require('cookie-parser')
var csrf = require('csurfer')
var bodyParser = require('body-parser')
var express = require('express')

// setup route middlewares
var csrfProtection = csrf({ cookie: true })
var parseForm = bodyParser.urlencoded({ extended: false })

// create express app
var app = express()

// parse cookies
// we need this because "cookie" is true in csrfProtection
app.use(cookieParser())

app.get('/form', csrfProtection, function(req, res) {
  // pass the csrfToken to the view
  res.render('send', { csrfToken: req.csrfToken() })
})

app.post('/process', parseForm, csrfProtection, function(req, res) {
  res.send('data is being processed')
})

Inside the view (depending on your template language; handlebars-style is demonstrated here), set the csrfToken value as the value of a hidden input field named _csrf:

<form action="/process" method="POST">
  <input type="hidden" name="_csrf" value="{{csrfToken}}">
  
  Favorite color: <input type="text" name="favoriteColor">
  <button type="submit">Submit</button>
</form>

Ignoring Routes

Note CSRF checks should only be disabled for requests that you expect to come from outside of your website. Do not disable CSRF checks for requests that you expect to only come from your website. An existing session, even if it belongs to an authenticated user, is not enough to protect against CSRF attacks.

The following is an example of how to order your routes so that certain endpoints do not check for a valid CSRF token.

var cookieParser = require('cookie-parser')
var csrf = require('csurfer')
var bodyParser = require('body-parser')
var express = require('express')

// create express app
var app = express()

// create api router
var api = createApiRouter()

// mount api before csrf is appended to the app stack
app.use('/api', api)

// now add csrf and other middlewares, after the "/api" was mounted
app.use(bodyParser.urlencoded({ extended: false }))
app.use(cookieParser())
app.use(csrf({ cookie: true }))

app.get('/form', function(req, res) {
  // pass the csrfToken to the view
  res.render('send', { csrfToken: req.csrfToken() })
})

app.post('/process', function(req, res) {
  res.send('csrf was required to get here')
})

function createApiRouter() {
  var router = new express.Router()

  router.post('/getProfile', function(req, res) {
    res.send('no csrf to get here')
  })

  return router
}

Custom error handling

When the CSRF token validation fails, an error is thrown that has err.code === 'EBADCSRFTOKEN'. This can be used to display custom error messages.

var bodyParser = require('body-parser')
var cookieParser = require('cookie-parser')
var csrf = require('csurfer')
var express = require('express')

var app = express()
app.use(bodyParser.urlencoded({ extended: false }))
app.use(cookieParser())
app.use(csrf({ cookie: true }))

// error handler
app.use(function (err, req, res, next) {
  if (err.code !== 'EBADCSRFTOKEN') return next(err)

  // handle CSRF token errors here
  res.status(403)
  res.send('form tampered with')
})

License

MIT