How to prevent CSRF attacks in ASP.NET Core

Cross-site request forgery (CSRF) is an attack that tricks an end user into executing undesirable actions while logged into a web application. Taking advantage of the authenticated user’s permissions, a CSRF attack dupes the victim into performing specific actions that benefit the attacker. For example, a CSRF attack could be used to make a purchase from a website or transfer money from the victim’s bank account.

This article talks about CSRF attacks, how they work, and how such attacks can be prevented in ASP.NET Core 6. To execute the code examples provided in this article, you should have Visual Studio 2022 installed in your system. If you don’t already have a copy, you can download Visual Studio 2022 here.

Create an ASP.NET Core MVC project in Visual Studio 2022

First off, let’s create an ASP.NET Core 6 project in Visual Studio 2022. Follow these steps:

  1. Launch the Visual Studio 2022 IDE.
  2. Click on “Create new project.”
  3. In the “Create new project” window, select “ASP.NET Core Web App (Model-View-Controller)” from the list of templates displayed.
  4. Click Next.
  5. In the “Configure your new project” window, specify the name and location for the new project.
  6. Optionally check the “Place solution and project in the same directory” check box, depending on your preferences.
  7. Click Next.
  8. In the “Additional Information” window shown next, select .NET 6.0 (Preview) as the target framework from the drop-down list at the top. Leave the “Authentication Type” as “None” (default).
  9. Ensure that the check boxes “Enable Docker,” “Configure for HTTPS,” and “Enable Razor runtime compilation” are unchecked as we won’t be using any of those features here.
  10. Click Create.

This will create a new ASP.NET Core MVC 6 project in Visual Studio. We’ll use this project in the subsequent sections of this article.

How do CSRF attacks work?

Cross-site request forgery is a kind of attack in which an attacker sends a malicious message to a web app that exploits the authentication cookies of the victim. These attacks are most commonly performed by tricking users with phishing emails to lure them to malicious websites. Let’s understand how this attack works.

Suppose you’ve logged into a bank website using forms authentication. The server issues you an authentication cookie and this cookie is set in your web browser. If the banking website trusts any request as long as it contains an authentication cookie, then the conditions are ripe for a CSRF attack.

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