Node.js Preventing Cross Site Request Forgery (CSRF)


Example

CSRF is an attack which forces end user to execute unwanted actions on a web application in which he/she is currently authenticated.

It can happen because cookies are sent with every request to a website - even when those requests come from a different site.

We can use csurf module for creating csrf token and validating it.

Example

var express = require('express')
var cookieParser = require('cookie-parser')    //for cookie parsing
var csrf = require('csurf')    //csrf module
var bodyParser = require('body-parser')    //for body parsing

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

// create express app
var app = express()

// parse cookies
app.use(cookieParser())

app.get('/form', csrfProtection, function(req, res) {
  // generate and 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')
})

So, when we access GET /form, it will pass the csrf token csrfToken to the view.

Now, inside the view, set the csrfToken value as the value of a hidden input field named _csrf.

e.g. for handlebar templates

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

e.g. for jade templates

form(action="/process" method="post")
    input(type="hidden", name="_csrf", value=csrfToken)

    span Name:
    input(type="text", name="name", required=true)
    br

    input(type="submit")

e.g. for ejs templates

<form action="/process" method="POST">
    <input type="hidden" name="_csrf" value="<%= csrfToken %>">
    Name: <input type="text" name="name">
    <button type="submit">Submit</button>
</form>