Laravel CSRF Token Mismatch

Introduction

CSRF (Cross-Site Request Forgery) is a type of online attack that targets web applications. It involves an attacker tricking a user into unknowingly executing a harmful action on a website, such as changing their password or making a purchase. Laravel provides built-in CSRF protection to safeguard your web application from such attacks.

When you submit a form using POST method in Laravel, a hidden CSRF token field is generated and included in the form. This token is then verified when the form is submitted to ensure that it originated from the same website and was not tampered with.

Error Message

When Laravel detects a token mismatch, it throws a TokenMismatchException with the following error message:

Illuminate\Session\TokenMismatchException
CSRF token mismatch.

Causes

There are several reasons that can cause a CSRF token mismatch error:

• A user leaves a form open for a long time, causing the CSRF token to expire.
• The user opens multiple tabs of the same website and submits forms from different tabs, causing a token mismatch.
• The session expires due to inactivity, causing a token mismatch.
• The CSRF token cookie is deleted by the user's browser.

Resolutions

Here are some possible solutions to fix the CSRF token mismatch error:

• Increase the value of the SESSION_LIFETIME variable in your .env file to extend the lifetime of your session.
• Update your Laravel version to the latest stable release to benefit from CSRF protection improvements.
• Use AJAX to submit forms, which will not cause the page to refresh and expire the CSRF token.
• Add a middleware to check for token mismatches and redirect the user to an error page when a mismatch is detected.

Conclusion

In conclusion, CSRF attacks are a serious threat to web applications and Laravel provides CSRF protection out-of-the-box. Token mismatches can occur due to a variety of reasons, but can be resolved by increasing session lifetime, updating Laravel version, or adding a middleware. By implementing the best practices for CSRF protection, you can greatly reduce the risk of your web application being hacked.