Skip to content
  • About
    • What is Symfony?
    • Community
    • News
    • Contributing
    • Support
  • Documentation
    • Symfony Docs
    • Symfony Book
    • Screencasts
    • Symfony Bundles
    • Symfony Cloud
    • Training
  • Services
    • SensioLabs Professional services to help you with Symfony
    • Platform.sh for Symfony Best platform to deploy Symfony apps
    • SymfonyInsight Automatic quality checks for your apps
    • Symfony Certification Prove your knowledge and boost your career
    • Blackfire Profile and monitor performance of your apps
  • Other
  • Blog
  • Download
sponsored by SensioLabs
  1. Home
  2. Documentation
  3. Security
  4. How to Implement CSRF Protection
  • Documentation
  • Book
  • Reference
  • Bundles
  • Cloud

Table of Contents

  • CSRF Protection in Symfony Forms
  • CSRF Protection in Login Forms
  • Generating and Checking CSRF Tokens Manually
  • CSRF Tokens and Compression Side-Channel Attacks

How to Implement CSRF Protection

Edit this page

How to Implement CSRF Protection

CSRF - or Cross-site request forgery - is a method by which a malicious user attempts to make your legitimate users unknowingly submit data that they don't intend to submit.

CSRF protection works by adding a hidden field to your form that contains a value that only you and your user know. This ensures that the user - not some other entity - is submitting the given data.

Before using the CSRF protection, install it in your project:

1
$ composer require symfony/security-csrf

Then, enable/disable the CSRF protection with the csrf_protection option (see the CSRF configuration reference for more information):

1
2
3
4
# config/packages/framework.yaml
framework:
    # ...
    csrf_protection: ~
1
2
3
4
5
6
7
8
9
10
11
12
13
14
<!-- config/packages/framework.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <framework:config>
        <framework:csrf-protection enabled="true"/>
    </framework:config>
</container>
1
2
3
4
5
6
7
8
// config/packages/framework.php
use Symfony\Config\FrameworkConfig;

return static function (FrameworkConfig $framework) {
    $framework->csrfProtection()
        ->enabled(true)
    ;
};

The tokens used for CSRF protection are meant to be different for every user and they are stored in the session. That's why a session is started automatically as soon as you render a form with CSRF protection.

Moreover, this means that you cannot fully cache pages that include CSRF protected forms. As an alternative, you can:

  • Embed the form inside an uncached ESI fragment and cache the rest of the page contents;
  • Cache the entire page and load the form via an uncached AJAX request;
  • Cache the entire page and use hinclude.js to load the CSRF token with an uncached AJAX request and replace the form field value with it.

CSRF Protection in Symfony Forms

Forms created with the Symfony Form component include CSRF tokens by default and Symfony checks them automatically, so you don't have to do anything to be protected against CSRF attacks.

By default Symfony adds the CSRF token in a hidden field called _token, but this can be customized on a form-by-form basis:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
// src/Form/TaskType.php
namespace App\Form;

// ...
use App\Entity\Task;
use Symfony\Component\OptionsResolver\OptionsResolver;

class TaskType extends AbstractType
{
    // ...

    public function configureOptions(OptionsResolver $resolver): void
    {
        $resolver->setDefaults([
            'data_class'      => Task::class,
            // enable/disable CSRF protection for this form
            'csrf_protection' => true,
            // the name of the hidden HTML field that stores the token
            'csrf_field_name' => '_token',
            // an arbitrary string used to generate the value of the token
            // using a different string for each form improves its security
            'csrf_token_id'   => 'task_item',
        ]);
    }

    // ...
}

You can also customize the rendering of the CSRF form field creating a custom form theme and using csrf_token as the prefix of the field (e.g. define {% block csrf_token_widget %} ... {% endblock %} to customize the entire form field contents).

CSRF Protection in Login Forms

See Security for a login form that is protected from CSRF attacks. You can also configure the CSRF protection for the logout action.

Generating and Checking CSRF Tokens Manually

Although Symfony Forms provide automatic CSRF protection by default, you may need to generate and check CSRF tokens manually for example when using regular HTML forms not managed by the Symfony Form component.

Consider a HTML form created to allow deleting items. First, use the csrf_token() Twig function to generate a CSRF token in the template and store it as a hidden form field:

1
2
3
4
5
6
<form action="{{ url('admin_post_delete', { id: post.id }) }}" method="post">
    {# the argument of csrf_token() is an arbitrary string used to generate the token #}
    <input type="hidden" name="token" value="{{ csrf_token('delete-item') }}"/>

    <button type="submit">Delete item</button>
</form>

Then, get the value of the CSRF token in the controller action and use the isCsrfTokenValid() method to check its validity:

1
2
3
4
5
6
7
8
9
10
11
12
13
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
// ...

public function delete(Request $request): Response
{
    $submittedToken = $request->request->get('token');

    // 'delete-item' is the same value used in the template to generate the token
    if ($this->isCsrfTokenValid('delete-item', $submittedToken)) {
        // ... do something, like deleting an object
    }
}

CSRF Tokens and Compression Side-Channel Attacks

BREACH and CRIME are security exploits against HTTPS when using HTTP compression. Attackers can leverage information leaked by compression to recover targeted parts of the plaintext. To mitigate these attacks, and prevent an attacker from guessing the CSRF tokens, a random mask is prepended to the token and used to scramble it.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.
TOC
    Version
    We stand with Ukraine.
    Version:

    Symfony 6.3 is backed by

    Symfony 6.3 is backed by

    Symfony 6.3 is backed by

    Symfony 6.3 is backed by

    Take the exam at home

    Take the exam at home

    Symfony Code Performance Profiling

    Symfony Code Performance Profiling

    Symfony footer

    ↓ Our footer now uses the colors of the Ukrainian flag because Symfony stands with the people of Ukraine.

    Avatar of Andrew Coulton, a Symfony contributor

    Thanks Andrew Coulton for being a Symfony contributor

    1 commit • 42 lines changed

    View all contributors that help us make Symfony

    Become a Symfony contributor

    Be an active part of the community and contribute ideas, code and bug fixes. Both experts and newcomers are welcome.

    Learn how to contribute

    Symfony™ is a trademark of Symfony SAS. All rights reserved.

    • What is Symfony?

      • Symfony at a Glance
      • Symfony Components
      • Case Studies
      • Symfony Releases
      • Security Policy
      • Logo & Screenshots
      • Trademark & Licenses
      • symfony1 Legacy
    • Learn Symfony

      • Symfony Docs
      • Symfony Book
      • Reference
      • Bundles
      • Best Practices
      • Training
      • eLearning Platform
      • Certification
    • Screencasts

      • Learn Symfony
      • Learn PHP
      • Learn JavaScript
      • Learn Drupal
      • Learn RESTful APIs
    • Community

      • SymfonyConnect
      • Support
      • How to be Involved
      • Code of Conduct
      • Events & Meetups
      • Projects using Symfony
      • Downloads Stats
      • Contributors
      • Backers
    • Blog

      • Events & Meetups
      • A week of symfony
      • Case studies
      • Cloud
      • Community
      • Conferences
      • Diversity
      • Documentation
      • Living on the edge
      • Releases
      • Security Advisories
      • SymfonyInsight
      • Twig
      • SensioLabs
    • Services

      • SensioLabs services
      • Train developers
      • Manage your project quality
      • Improve your project performance
      • Host Symfony projects

      Deployed on

    Follow Symfony

    Search by Algolia