How to Implement CSRF Protection
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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 (which in turn requires installing the Symfony Form component):
1
$ composer require symfony/security-csrf symfony/form
Then, enable/disable the CSRF protection with the csrf_protection
option
(see the CSRF configuration reference
for more information):
- YAML
- XML
- PHP
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# config/packages/framework.yaml
framework:
# ...
csrf_protection: ~
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<!-- 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
http://symfony.com/schema/dic/services/services-1.0.xsd
http://symfony.com/schema/dic/symfony
http://symfony.com/schema/dic/symfony/symfony-1.0.xsd">
<framework:config>
<framework:csrf-protection enabled="true" />
</framework:config>
</container>
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// config/packages/framework.php
$container->loadFromExtension('framework', array(
'csrf_protection' => null,
));
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',
));
}
// ...
}
Caution
Since the token is stored in the session, a session is started automatically as soon as you render a form with CSRF protection.
Caution
CSRF tokens are meant to be different for every user. Beware of that when caching pages that include forms containing CSRF tokens. For more information, see Caching Pages that Contain CSRF Protected Forms.
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.
Tip
If you're using a Guard Authenticator, you'll need to validate the CSRF token manually inside of that class. See How to Create a Custom Authentication System with Guard for details.
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:
- YAML
- XML
- PHP
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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.
Tip
You can change the name of the field by setting csrf_parameter
and change
the token ID by setting csrf_token_id
in your configuration:
- YAML
- XML
- PHP
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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
}
}