How to Fix CSRF Error in .NET

A CSRF Error in .NET usually signals a straightforward configuration problem. Here's exactly how to fix it.

Understanding the Problem

CSRF errors happen when your application can't verify that a form submission originated from your own site. Without proper token validation, the server rejects the request to prevent malicious cross-site attacks.

Solution

The key is to enable the built-in antiforgery service and decorate POST endpoints:

// Startup.cs
services.AddAntiforgery(options => {
    options.HeaderName = "X-CSRF-TOKEN";
});

// Controller
[ValidateAntiForgeryToken]
[HttpPost]
public IActionResult Submit(FormModel model) {
    return Ok();
}

Common Pitfall

Don't overlook your CI/CD pipeline — sometimes the fix works locally but the deployment environment has different defaults. Make sure your .NET configuration is explicit rather than relying on defaults. Review your .NET project's dependency tree after applying this fix. Outdated packages are a common source of subtle incompatibilities.

Confirming It Works

To confirm the fix is working, check your .NET application logs for any remaining error traces. You should see clean request/response cycles without the previous error. Deploy to a staging environment to verify the fix holds under production-like conditions.

Going Forward

Tip: Use [Bugsly](https://bugsly.dev) to automatically detect and alert you to .NET errors like this in production before your users notice them.