@companieshouse/web-security-node

web-security-node

Security for web applications in node

Cross Site Request Forgery (CSRF) protection

This library provides a Express middleware Request Handler which will protect an application from Cross Site Request Forgery (CSRF) attacks. The middleware works by looking for a token within the request which should match a token held within the CHS session. The middleware will expect all requests from methods which modify data (for example POST/DELETE/PUT) to include the CSRF token. This implements a Synchronisation Token Pattern approach

Installation instructions

1. Install the library (if not already installed).

   npm i @companieshouse/web-security-node@^4.1.0

2. Define the options for the middleware and add the middleware to the application. Optionally, you can add the error handler too.

   import { CsrfProtectionMiddleware } from " @companieshouse/web-security-node"
   import {
       SessionStore,
       SessionMiddleware
   } from '@companieshouse/node-session-handler';
   import express from "express";
   import cookieParser from 'cookie-parser';
   import Redis from 'ioredis';
   
   
   const app = express();
   
   // apply other middlewares
   
   app.use(cookieParser());
   app.use(express.urlencoded({ extended: true }));
   const cookieName = '__SID'
   
   const cookieConfig = {
       cookieName,
       cookieSecret: config.COOKIE_SECRET,
       cookieDomain: config.COOKIE_DOMAIN,
       cookieTimeToLiveInSeconds: parseInt(config.DEFAULT_SESSION_EXPIRATION, 10)
   };
   const sessionStore = new SessionStore(new Redis(`redis://${config.CACHE_SERVER}`));
   // Important the session Middleware is required before this middleware since the
   // token is stored within the session
   app.use(SessionMiddleware(cookieConfig, sessionStore));
   const csrfMiddlewareOptions = {
       sessionStore,
       enabled: true,
       sessionCookieName: cookieName
   }
   app.use(createLoggerMiddleware(config.applicationNamespace));
   
   // It is important that CSRF Protection follows the Sesion and urlencoded
   // Middlewares, maybe put at end of the middleware chain (before
   // controllers)
   app.use(CsrfProtectionMiddleware(csrfMiddlewareOptions))
   app.use(helmet());
   
   // Add other middlewares and routers

3. Amend the Nunjucks configuration to add the thirdparty templates from this library:

   nunjucks
     .configure([
         "dist/views",
         "node_modules/govuk-frontend/",
         "node_modules/govuk-frontend/components/",
         "node_modules/@companies-house/"
     ], nunjucksConfig)

4. In each form which submits data (or modifies data) add the following macro call

   {% from "web-security-node/components/csrf-token-input/macro.njk" import csrfTokenInput %}
   
   <form action="POST">
       {{
           csrfTokenInput({
               csrfToken: csrfToken
           })
       }}
       <!-- Other form items ommitted -->
   </form>

5. Create an CSRF error page template and add the following macro call (or amend an existing template)

   {% from "web-security-node/components/csrf-error/macro.njk" import csrfError %}
   
   {{
     csrfError({})
   }}

6. Create an error handler for CSRF Errors, you could start with:

   import { ErrorRequestHandler, NextFunction, Request, Response } from 'express'
   import {
       CsrfError
   } from '@companieshouse/web-security-node'
   
   // TODO: Enter the template name here instead of <TEMPLATE NAME>
   const csrfErrorTemplateName = "<TEMPLATE NAME>";
   
   const csrfErrorHandler = (err: CsrfError | Error, _: Request,
     res: Response, next: NextFunction) => {
     
     // handle non-CSRF Errors immediately
     if (!(err instanceof CsrfError)) {
       next(err);
     }
   
     return res.status(403).render(
       csrfErrorTemplateName, {
         // TODO: Complete this with any information required by your error
         // template, the CSRF Error component requires no information currently
       }
     )
   };

7. Add the error handler to your application before the default Error Handler (to prevent CSRF errors being handled as normal exceptions.)

API

CsrfOptions interface

Provides configuration to the middleware.

Properties

• enabled (boolean required) - whether or not to apply CSRF protections

• sessionStore (SessionStore required) - a SessionStore instance to manage the CHS session

• sessionCookieName (string) - name of the cookie storing the signed Session ID

• csrfTokenFactory (supplier of string) - a callable when called will return a string to use as the session's CSRF token. Has signature:

  () => string

  Defaults to a uuid supplier if not supplied.

• createWhenCsrfTokenAbsent (boolean) - whether to generate a new CSRF token if not present in the session. Only run on non-mutable requests (e.g. GET)

• headerName (string) - name of the header to check. Defaults to X-CSRF-TOKEN

• parameterName (string) - name of the parameter in the request body to check. Defaults to _csrf.

CsrfProtectionMiddleware function

A Request Handler capable of being used as a express Middleware function. Its responsibility is checking that all mutable requests include a csrf token which indicates that they originated from the same CHS session and not an CSRF attempt. The middleware expects that all mutable requests contain a token which matches a token stored within the CHS session. It will add csrfToken to locals so that views can reference it as a variable.

Parameters

• options - (CsrfOptions required) - the configuration for the middleware is provided as an object which implements the interface CsrfOptions

defaultCsrfTokenFactory function

This function is the default CSRF issuing function, it essentially provides an uuid.

Exceptions

CsrfError - Base class for all errors thrown by middleware

SessionUnsetError - Thrown when a mutable request is received and the session has not been set on the request. Likely due to application misconfiguration. Check that the session handler is placed before the CSRF middleware.

CsrfTokensMismatchError - Thrown when the CSRF token is either missing in the mutable request or does not match the CSRF token within the CHS session.

MissingCsrfSessionToken - Thrown when there is no CSRF token within the session to match the request's Token against.