Purpose Of ValidateAntiForgeryToken In MVC Application

1. Step 1 - Create two MVC applications with default internet template and give those names as CrossSite_RequestForgery and Attack_Application respectively.
   
   
2. Now, open CrossSite_RequestForgery application's Web Config and change the connection string with the one given below and then save.
   
   1. <connectionStrings>
   2. <add name="DefaultConnection" connectionString="Data Source=local\SQLEXPRESS;Initial
   3. Catalog=CSRF;Integrated Security=true;" providerName="System.Data.SqlClient" /> </connectionStrings>
3. Now, click on Tools >> NuGet Package Manager, then Package Manager Console
   
4. Now, run the below mentioned three commands in Package Manager Console to create the database.
   
   Enable-Migrations add-migration first update-database
   
   Important Notes - I have created database with code first approach because I want to make this example in the way developers work. You can create database manually also. It's your choice.
   
   
5. Now, open Account Controller. Here, you will see a register method whose type is post. Above this method, there should be an attribute available as [ValidateAntiForgeryToken]. Comment this attribute. Now, right click on register and click go to View. There again, you will find an html helper as @Html.AntiForgeryToken() . Comment this one also. Run the application and click on register button. The URL will be open as:
   
   http://localhost:52269/Account/Register
   
   Notes- I know now the question being raised in all readers’ minds is why these two helpers need to be commented, as everyone knows these are used to validate request. Then, I just want to let you all know that this is just because I want to show the difference after and before applying these helpers.
   
   
6. Now, open the second application which is Attack_Application. Then, open Register method of Account Controller. Just change the POST method with the simple one, shown below.
   
   1. <form method="post" action="http://localhost:52269/Account/Register">
   2. <fieldset>
   3. <legend>Registration Form</legend>
   4. <ol>
   5. <li> @Html.LabelFor(m => m.UserName) @Html.TextBoxFor(m => m.UserName) </li>
   6. <li> @Html.LabelFor(m => m.Password) @Html.PasswordFor(m => m.Password) </li>
   7. <li> @Html.LabelFor(m => m.ConfirmPassword) @Html.PasswordFor(m => m.ConfirmPassword) </li>
   8. </ol> <input type="submit" value="Register" /> </fieldset>
   9. </form>
7. Now, suppose you are a hacker and you know the URL from where you can register user in CrossSite_RequestForgery application. Now, you created a Forgery site as Attacker_Application and just put the same URL in post method.
   
   
8. Run this application now and fill the register fields and click on register. You will see you are registered in CrossSite_RequestForgery application. If you check the database of CrossSite_RequestForgery application then you will see and entry you have entered.
   
   
9. Important - Now, open CrossSite_RequestForgery application and comment out the token in Account Controller and register the View. Try to register again with the same process. Then, an error will occur as below.
   
   Server Error in '/' Application.
   ________________________________________
   The required anti-forgery cookie "__RequestVerificationToken" is not present.
   
   This is what the concept says. What we add in View i.e. @Html.AntiForgeryToken() generates __RequestVerificationToken on load time and [ValidateAntiForgeryToken] available on Controller method. Match this token on post time. If token is the same, then it means this is a valid request.

Hope you understand the concept and like the article. Happy Coding.