@dr.pogodin/csurf
v1.14.1
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CSRF token middleware for ExpressJS
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CSURF
Node.js CSRF protection middleware for ExpressJS.
Contributors
+ contributors of the original csurf
This is a fork of the original csurf package which was deprecated by its author with doubtful reasoning (in the nutshell the package was alright, but author did not want to maintain it anymore). It is published to NPM as @dr.pogodin/csurf, its version 1.11.0 exactly matches the same, latest version of the original package, its versions starting from 1.12.0 have all dependencies updated to their latest versions, and misc maintenance performed as needed. To migrate from the original csurf just replace all references to it by @dr.pogodin/csurf.
Security Considerations
Double Submit Cookie — This mode of CSRF protection relies on the inability of code from a 3rd-party origin to read/write cookies stored, and sent by browser for the protected origin. Sure, there are ways you may ruin it, if you don't know what you are doing:
- Serving your website over unsecure HTTP connection — a man in the middle might read your cookies (and everything else) you send over, and exploit your negligence in all posible ways, including but not limited to by-passing double submit cookie CSRF protection.
- Allowing XSS injection — if 3rd party is able to inject arbitrary code inside your own website, sure they can read the cookie and by-pass CSRF protection.
- Allowing 3rd parties to control your sub-domains (a code running on sub-domain may shadow CSRF cookie set by the protected domain, thus allowing to by-pass CSRF protection).
- etc.
This library has options allowing to mitigate these possibilities (by opting for various security options for CSRF cookies, which will instruct the browser to not pass CSRF cookie over insecure connections, etc.), but, by default, the library does not enforce these options.
Some argue that not enforcing these options by default is against security, and requires deprecation of the library (like happened to its upstream original); IMHO, enforcing these options just adds headache in more common scenarios, and here is no security issue with the library, as long as it does exactly what users asks it to do.
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:
If you have questions on how this module is implemented, please read Understanding CSRF.
Installation
This is a Node.js module available through the
npm registry. Installation is done using the
npm install
command:
$ npm install --save @dr.pogodin/csurf
API
var csurf = require('@dr.pogodin/csurf')
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
. Storing the token secret in a cookie implements
the double submit cookie pattern.
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'/'
).signed
- indicates if the cookie should be signed (defaults tofalse
).secure
- marks the cookie to be used with HTTPS only (defaults tofalse
).maxAge
- the number of seconds after which the cookie will expire (defaults to session length).httpOnly
- flags the cookie to be accessible only by the web server (defaults tofalse
).sameSite
- sets the same site policy for the cookie(defaults tofalse
). This can be set to'strict'
,'lax'
,'none'
, ortrue
(which maps to'strict'
).domain
- sets the domain the cookie is valid on(defaults to current domain).
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 thebody-parser
module.req.query._csrf
- a built-in from Express.js to read from the URL query string.req.headers['csrf-token']
- theCSRF-Token
HTTP request header.req.headers['xsrf-token']
- theXSRF-Token
HTTP request header.req.headers['x-csrf-token']
- theX-CSRF-Token
HTTP request header.req.headers['x-xsrf-token']
- theX-XSRF-Token
HTTP request header.
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('@dr.pogodin/csurf')
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>
Using AJAX
When accessing protected routes via ajax both the csrf token will need to be passed in the request. Typically this is done using a request header, as adding a request header can typically be done at a central location easily without payload modification.
The CSRF token is obtained from the req.csrfToken()
call on the server-side.
This token needs to be exposed to the client-side, typically by including it in
the initial page content. One possibility is to store it in an HTML <meta>
tag,
where value can then be retrieved at the time of the request by JavaScript.
The following can be included in your view (handlebar example below), where the
csrfToken
value came from req.csrfToken()
:
<meta name="csrf-token" content="{{csrfToken}}">
The following is an example of using the
Fetch API to post
to the /process
route with the CSRF token from the <meta>
tag on the page:
// Read the CSRF token from the <meta> tag
var token = document.querySelector('meta[name="csrf-token"]').getAttribute('content')
// Make a request using the Fetch API
fetch('/process', {
credentials: 'same-origin', // <-- includes cookies in the request
headers: {
'CSRF-Token': token // <-- is the csrf token as a header
},
method: 'POST',
body: {
favoriteColor: 'blue'
}
})
Single Page Application (SPA)
Many SPA frameworks like Angular have CSRF support built in automatically.
Typically they will reflect the value from a specific cookie, like
XSRF-TOKEN
(which is the case for Angular).
To take advantage of this, set the value from req.csrfToken()
in the cookie
used by the SPA framework. This is only necessary to do on the route that
renders the page (where res.render
or res.sendFile
is called in Express,
for example).
The following is an example for Express of a typical SPA response:
app.all('*', function (req, res) {
res.cookie('XSRF-TOKEN', req.csrfToken())
res.render('index')
})
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('@dr.pogodin/csurf')
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('@dr.pogodin/csurf')
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')
})