c# - AngularJS Web Api AntiForgeryToken CSRF

Question

I have an AngularJS Single Page Application (SPA) hosted by an ASP.NET MVC application.
The back-end is ASP.NET Web Api.

I would like to protect it against CSRF attacks by generating an AntiForgeryToken in the ASP.NET MVC part, pass it to AngularJS, and then have Web Api validate the AntiForgeryToken received from the subsequent AngularJS calls.

“Cross-Site Request Forgery (CSRF) is an attack that forces an end user to execute unwanted actions on a web application in which they're currently authenticated. CSRF attacks specifically target state-changing requests, not theft of data, since the attacker has no way to see the response to the forged request. With a little help of social engineering (such as sending a link via email or chat), an attacker may trick the users of a web application into executing actions of the attacker's choosing. If the victim is a normal user, a successful CSRF attack can force the user to perform state changing requests like transferring funds, changing their email address, and so forth. If the victim is an administrative account, CSRF can compromise the entire web application.”
- Open Web Application Security Project (OWASP)

question from:https://stackoverflow.com/questions/32460196/angularjs-web-api-antiforgerytoken-csrf

Answer 1

Add to the ASP.NET MVC View that serves the AngularJS SPA, let's say ViewsHomeIndex.cshtml, the HTML helper that generates the AntiForgeryToken.

@Html.AntiForgeryToken();

Configure AngularJS to pass the above generated AntiForgeryToken as Request Header.

angular.module('app')
.run(function ($http) {
    $http.defaults.headers.common['X-XSRF-Token'] =
        angular.element('input[name="__RequestVerificationToken"]').attr('value');
});

Create a custom Web API Filter to validate all non-GET requests (PUT, PATCH, POST, DELETE).

This assumes that all your GET requests are safe and don't need protecting.
If that's not the case, remove the if (actionContext.Request.Method.Method != "GET") exclusion.

using System;
using System.Linq;
using System.Net.Http;
using System.Web.Helpers;
using System.Web.Http.Filters;

namespace Care.Web.Filters
{
    public sealed class WebApiValidateAntiForgeryTokenAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(
            System.Web.Http.Controllers.HttpActionContext actionContext)
        {
            if (actionContext == null)
            {
                throw new ArgumentNullException("actionContext");
            }

            if (actionContext.Request.Method.Method != "GET")
            {
                var headers = actionContext.Request.Headers;
                var tokenCookie = headers
                    .GetCookies()
                    .Select(c => c[AntiForgeryConfig.CookieName])
                    .FirstOrDefault();

                var tokenHeader = string.Empty;
                if (headers.Contains("X-XSRF-Token"))
                {
                    tokenHeader = headers.GetValues("X-XSRF-Token").FirstOrDefault();
                }

                AntiForgery.Validate(
                    tokenCookie != null ? tokenCookie.Value : null, tokenHeader);
            }

            base.OnActionExecuting(actionContext);
        }
    }
}

Register the newly created filter as a global one, in Global.asax.cs.

    private static void RegisterWebApiFilters(HttpFilterCollection filters)
    {
        filters.Add(new WebApiValidateAntiForgeryTokenAttribute());
    }

Alternatively, if you don't wish to add this filter globally, you can put it only on certain Web API actions, like this

[WebApiValidateAntiForgeryToken]

This, of course, is by definition less secure, as there's always the chance that you'll forget to apply the attribute to an action that needs it.

Also, note that you must have the Microsoft.AspNet.WebApi.Core package in order to have access to System.Web.Http namespace. You can install it via NuGet with Install-Package Microsoft.AspNet.WebApi.Core.

This post has been heavily inspired by this blog post.