How Does ValidateAntiForgeryToken Prevent CSRF Attacks in ASP.NET MVC?

ValidateAntiForgeryToken: Its Purpose and Implementation

Forms in MVC web applications are often targets for cross-site request forgery (CSRF) attacks. CSRF attacks occur when malicious websites send requests to trusted websites and trick the browsers of authorized users into submitting those requests, thereby allowing attackers to perform unauthorized actions.

To address this vulnerability, the .NET MVC framework offers the ValidateAntiForgeryToken attribute, which plays a vital role in preventing CSRF attacks. This attribute ensures that forms submitted to a specific action method have actually originated from the server and not from an external source.

How ValidateAntiForgeryToken Works

When an action method is decorated with ValidateAntiForgeryToken, the MVC framework generates a unique, one-time token and embeds it in the HTML form's hidden field using the @Html.AntiForgeryToken() helper method. This token is unique to the user, the session, and the browser.

When the user submits the form, the framework compares the token in the hidden field with the token it generated earlier. If the tokens match, it validates the form submission. Otherwise, it raises an error and rejects the submission, mitigating the CSRF attack.

Example Usage

To implement the ValidateAntiForgeryToken attribute in MVC 4, follow these steps:

1. Decorate the action method you want to protect with the [ValidateAntiForgeryToken] attribute:

   [HttpPost]
   [ValidateAntiForgeryToken]
   public ActionResult Create(MyModel model)
   {
    // Code to handle the form submission
   }

2. Add a call to @Html.AntiForgeryToken() within the form's form tag:

   <form action="@Url.Action("Create", "MyController")" method="post">
    @Html.AntiForgeryToken()
    <!-- Other form controls -->
   </form>

Note: The @Html.AntiForgeryToken() helper method must be placed within the form's form tag, but before all other form controls.

By following these steps, you can effectively safeguard your MVC web application against CSRF attacks and ensure the integrity of your form submissions.

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