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:

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

class TaskType extends AbstractType
{
    // ...

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults(array(
            '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',
        ));
    }

    // ...
}

CSRF Protection in Login Forms

Login CSRF attacks can be prevented using the same technique of adding hidden CSRF tokens into the login forms. The Security component already provides CSRF protection, but you need to configure some options before using it.

First, configure the CSRF token provider used by the form login in your security configuration. You can set this to use the default provider available in the security component:

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# config/packages/security.yaml
security:
    # ...

    firewalls:
        secured_area:
            # ...
            form_login:
                # ...
                csrf_token_generator: security.csrf.token_manager

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<!-- config/packages/security.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<srv:container xmlns="http://symfony.com/schema/dic/security"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:srv="http://symfony.com/schema/dic/services"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        http://symfony.com/schema/dic/services/services-1.0.xsd">

    <config>
        <!-- ... -->

        <firewall name="secured_area">
            <!-- ... -->
            <form-login csrf-token-generator="security.csrf.token_manager" />
        </firewall>
    </config>
</srv:container>

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// config/packages/security.php
$container->loadFromExtension('security', array(
    // ...

    'firewalls' => array(
        'secured_area' => array(
            // ...
            'form_login' => array(
                // ...
                'csrf_token_generator' => 'security.csrf.token_manager',
            ),
        ),
    ),
));

Then, use the csrf_token() function in the Twig template to generate a CSRF token and store it as a hidden field of the form. By default, the HTML field must be called _csrf_token and the string used to generate the value must be authenticate:

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{# templates/security/login.html.twig #}

{# ... #}
<form action="{{ path('login') }}" method="post">
    {# ... the login fields #}

    <input type="hidden" name="_csrf_token"
        value="{{ csrf_token('authenticate') }}"
    >

    <button type="submit">login</button>
</form>

After this, you have protected your login form against CSRF attacks.

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# config/packages/security.yaml
security:
    # ...

    firewalls:
        secured_area:
            # ...
            form_login:
                # ...
                csrf_parameter: _csrf_security_token
                csrf_token_id: a_private_string

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<!-- config/packages/security.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<srv:container xmlns="http://symfony.com/schema/dic/security"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:srv="http://symfony.com/schema/dic/services"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        http://symfony.com/schema/dic/services/services-1.0.xsd">

    <config>
        <!-- ... -->

        <firewall name="secured_area">
            <!-- ... -->
            <form-login csrf-parameter="_csrf_security_token"
                csrf-token-id="a_private_string"
            />
        </firewall>
    </config>
</srv:container>

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// config/packages/security.php
$container->loadFromExtension('security', array(
    // ...

    'firewalls' => array(
        'secured_area' => array(
            // ...
            'form_login' => array(
                // ...
                'csrf_parameter' => '_csrf_security_token',
                'csrf_token_id'  => 'a_private_string',
            ),
        ),
    ),
));

CSRF Protection in HTML Forms

It's also possible to add CSRF protection to regular HTML forms not managed by the Symfony Form component, for example the simple forms used to delete items. First, use the csrf_token() function in the Twig template to generate a CSRF token and store it as a hidden field of the form:

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<form action="{{ url('admin_post_delete', { id: post.id }) }}" method="post">
    {# the argument of csrf_token() is an arbitrary value 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() to check its validity:

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use Symfony\Component\HttpFoundation\Request;
// ...

public function delete(Request $request)
{
    $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
    }
}