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csurf

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

This is a Node.js module available through the npm registry. Installation is done using the npm install command:

$ npm install csurf

API

varcsurf=require('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 to false).
• secure - marks the cookie to be used with HTTPS only (defaults to false).
• 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 to false).
• sameSite - sets the same site policy for the cookie(defaults to false). This can be set to 'strict', 'lax', 'none', or true (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 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.

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.

varcookieParser=require('cookie-parser')varcsrf=require('csurf')varbodyParser=require('body-parser')varexpress=require('express')// setup route middlewaresvarcsrfProtection=csrf({cookie: true})varparseForm=bodyParser.urlencoded({extended: false})// create express appvarapp=express()// parse cookies// we need this because "cookie" is true in csrfProtectionapp.use(cookieParser())app.get('/form',csrfProtection,function(req,res){// pass the csrfToken to the viewres.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:

<formaction="/process" method="POST"><inputtype="hidden" name="_csrf" value="{{csrfToken}}">
Favorite color: <inputtype="text" name="favoriteColor"><buttontype="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():

<metaname="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> tagvartoken=document.querySelector('meta[name="csrf-token"]').getAttribute('content')// Make a request using the Fetch APIfetch('/process',{credentials: 'same-origin',// <-- includes cookies in the requestheaders: {'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.

varcookieParser=require('cookie-parser')varcsrf=require('csurf')varbodyParser=require('body-parser')varexpress=require('express')// create express appvarapp=express()// create api routervarapi=createApiRouter()// mount api before csrf is appended to the app stackapp.use('/api',api)// now add csrf and other middlewares, after the "/api" was mountedapp.use(bodyParser.urlencoded({extended: false}))app.use(cookieParser())app.use(csrf({cookie: true}))app.get('/form',function(req,res){// pass the csrfToken to the viewres.render('send',{csrfToken: req.csrfToken()})})app.post('/process',function(req,res){res.send('csrf was required to get here')})functioncreateApiRouter(){varrouter=newexpress.Router()router.post('/getProfile',function(req,res){res.send('no csrf to get here')})returnrouter}

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.

varbodyParser=require('body-parser')varcookieParser=require('cookie-parser')varcsrf=require('csurf')varexpress=require('express')varapp=express()app.use(bodyParser.urlencoded({extended: false}))app.use(cookieParser())app.use(csrf({cookie: true}))// error handlerapp.use(function(err,req,res,next){if(err.code!=='EBADCSRFTOKEN')returnnext(err)// handle CSRF token errors hereres.status(403)res.send('form tampered with')})

References

• Cross-side request forgery on Wikipedia
• OWASP Cross-Site Request Forgery Prevention Cheat Sheet

License

MIT