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nicolas-grekasnicolas-grekas
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[Security] Implement double-submit CSRF protection
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6 files changed

+211
-1
lines changed

6 files changed

+211
-1
lines changed

‎src/Symfony/Bundle/FrameworkBundle/DependencyInjection/Configuration.php‎

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@@ -237,6 +237,8 @@ private function addFormSection(ArrayNodeDefinition $rootNode, callable $enableI
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->children()
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->booleanNode('enabled')->defaultNull()->end() // defaults to framework.csrf_protection.enabled
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->scalarNode('field_name')->defaultValue('_token')->end()
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->scalarNode('header_name')->defaultValue('x-csrf-token')->end()
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->booleanNode('accept_as_fallback')->defaultFalse()->end()
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->end()
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->end()
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->end()

‎src/Symfony/Bundle/FrameworkBundle/DependencyInjection/FrameworkExtension.php‎

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@@ -149,6 +149,7 @@
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use Symfony\Component\Security\Core\AuthenticationEvents;
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use Symfony\Component\Security\Core\Exception\AuthenticationException;
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use Symfony\Component\Security\Csrf\CsrfTokenManagerInterface;
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use Symfony\Component\Security\Csrf\DoubleSubmitCsrfTokenManager;
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use Symfony\Component\Semaphore\PersistingStoreInterface as SemaphoreStoreInterface;
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use Symfony\Component\Semaphore\Semaphore;
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use Symfony\Component\Semaphore\SemaphoreFactory;
@@ -763,6 +764,12 @@ private function registerFormConfiguration(array $config, ContainerBuilder $cont
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$container->setParameter('form.type_extension.csrf.enabled', true);
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$container->setParameter('form.type_extension.csrf.field_name', $config['form']['csrf_protection']['field_name']);
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$container->setParameter('form.type_extension.csrf.header_name', $config['form']['csrf_protection']['header_name']);
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$container->setParameter('form.type_extension.csrf.accept_as_fallback', $config['form']['csrf_protection']['accept_as_fallback']);
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if (!$config['form']['csrf_protection']['header_name'] || !class_exists(DoubleSubmitCsrfTokenManager::class)) {
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$container->setAlias('form.type_extension.csrf.token_manager', 'security.csrf.token_manager');
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}
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} else {
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$container->setParameter('form.type_extension.csrf.enabled', false);
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}

‎src/Symfony/Bundle/FrameworkBundle/Resources/config/form_csrf.php‎

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@@ -12,18 +12,28 @@
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namespace Symfony\Component\DependencyInjection\Loader\Configurator;
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use Symfony\Component\Form\Extension\Csrf\Type\FormTypeCsrfExtension;
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use Symfony\Component\Security\Csrf\DoubleSubmitCsrfTokenManager;
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return static function (ContainerConfigurator $container) {
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$container->services()
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->set('form.type_extension.csrf', FormTypeCsrfExtension::class)
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->args([
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service('security.csrf.token_manager'),
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service('form.type_extension.csrf.token_manager'),
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param('form.type_extension.csrf.enabled'),
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param('form.type_extension.csrf.field_name'),
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service('translator')->nullOnInvalid(),
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param('validator.translation_domain'),
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service('form.server_params'),
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])
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->tag('form.type_extension')
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->set('form.type_extension.csrf.token_manager', DoubleSubmitCsrfTokenManager::class)
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->args([
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service('request_stack'),
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service('logger')->nullOnInvalid(),
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param('form.type_extension.csrf.header_name'),
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param('form.type_extension.csrf.accept_as_fallback'),
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])
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->tag('monolog.logger', ['channel' => 'request'])
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;
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};

‎src/Symfony/Component/Form/Extension/Csrf/Type/FormTypeCsrfExtension.php‎

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@@ -73,6 +73,7 @@ public function finishView(FormView $view, FormInterface $form, array $options):
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$csrfForm = $factory->createNamed($options['csrf_field_name'], HiddenType::class, $data, [
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'block_prefix' => 'csrf_token',
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'mapped' => false,
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'attr' => ['data--csrf-protection' => true],
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]);
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$view->children[$options['csrf_field_name']] = $csrfForm->createView($view);

‎src/Symfony/Component/Security/Csrf/CHANGELOG.md‎

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@@ -1,6 +1,11 @@
11
CHANGELOG
22
=========
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7.2
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---
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* Add `DoubleSubmitCsrfTokenManager`
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49
6.0
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---
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‎src/Symfony/Component/Security/Csrf/DoubleSubmitCsrfTokenManager.php‎

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@@ -0,0 +1,185 @@
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<?php
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/*
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* This file is part of the Symfony package.
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*
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* (c) Fabien Potencier <fabien@symfony.com>
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*
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* For the full copyright and license information, please view the LICENSE
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* file that was distributed with this source code.
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*/
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namespace Symfony\Component\Security\Csrf;
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use Psr\Log\LoggerInterface;
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use Symfony\Component\HttpFoundation\Request;
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use Symfony\Component\HttpFoundation\RequestStack;
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use Symfony\Component\HttpFoundation\Response;
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use Symfony\Component\HttpFoundation\Session\Session;
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use Symfony\Component\HttpKernel\Event\ResponseEvent;
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/**
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* This CSRF token manager uses a combination of cookie and headers to validate non-persistent tokens.
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*
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* Double-Submit Validation: A JavaScript snippet on the client side is responsible for performing the
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* double-submission. If the double-submit information is missing, we fall back to using the Origin or
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* Referer headers.
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*
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* Fallback Scenarios: If neither double-submit nor Origin/Referer headers are available, it typically
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* indicates that JavaScript is disabled on the client side (unless the JavaScript snippet was not
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* properly implemented), or that the Origin header was not sent.
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*
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* By default, requests lacking both double-submit and origin information are deemed insecure.
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*
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* Security Consistency: When a session is found, a behavioral check is added to ensure that the
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* validation method does not downgrade from double-submit to origin checks, or from origin checks to
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* the accept fallback. This prevents attackers from exploiting potentially less secure validation
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* methods once a more secure method has been confirmed as functional.
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*
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* @author Nicolas Grekas <p@tchwork.com>
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*/
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final class DoubleSubmitCsrfTokenManager implements CsrfTokenManagerInterface
42+
{
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public const HEADER_NAME = 'x-csrf-token';
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public function __construct(
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private RequestStack $requestStack,
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private ?LoggerInterface $logger = null,
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private string $headerName = self::HEADER_NAME,
49+
private bool $acceptAsFallback = false,
50+
) {
51+
}
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public function getToken(string $tokenId): CsrfToken
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{
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return new CsrfToken($tokenId, $this->headerName);
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}
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public function refreshToken(string $tokenId): CsrfToken
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{
60+
return new CsrfToken($tokenId, $this->headerName);
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}
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public function removeToken(string $tokenId): ?string
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{
65+
return null;
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}
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public function isTokenValid(CsrfToken $token): bool
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{
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// This token is not for us
71+
if ($token->getValue() !== $this->headerName) {
72+
$this->logger?->debug('CSRF validation failed: Unknown CSRF token.');
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return false;
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}
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if (!$request = $this->requestStack->getCurrentRequest()) {
78+
$this->logger?->debug('CSRF validation failed: No request found.');
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return false;
81+
}
82+
83+
if (false === $isValidOrigin = $this->isValidOrigin($request)) {
84+
$this->logger?->debug('CSRF validation failed: Origin doesn\'t match.');
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86+
return false;
87+
}
88+
89+
if ($this->isValidDoubleSubmit($request)) {
90+
// Mark the request as validated using double-submit info
91+
$request->attributes->set($this->headerName, 'double-submit');
92+
$this->logger?->debug('CSRF validation accepted using double-submit info.');
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return true;
95+
}
96+
97+
// Opportunistically lookup at the session for a previous CSRF validation strategy
98+
$session = $request->hasPreviousSession() ? $request->getSession() : null;
99+
$usageIndexValue = $session instanceof Session ? $usageIndexReference = &$session->getUsageIndex() : 0;
100+
$usageIndexReference = \PHP_INT_MIN;
101+
$csrfProtection = $session?->get($this->headerName);
102+
$usageIndexReference = $usageIndexValue;
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104+
// If a previous request was validated using double-submit info, stick to it
105+
if ('double-submit' === $csrfProtection) {
106+
$this->logger?->debug('CSRF validation failed: double-submit info was used in a previous request but didn\'t pass this time.');
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108+
return false;
109+
}
110+
111+
// If a previous request was validated using origin info, stick to it
112+
if ('origin' === $csrfProtection && null === $isValidOrigin) {
113+
$this->logger?->debug('CSRF validation failed: origin info was used in a previous request but didn\'t pass this time.');
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return false;
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}
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118+
if (true === $isValidOrigin) {
119+
// Mark the request as validated using origin info
120+
$request->attributes->set($this->headerName, 'origin');
121+
$this->logger?->debug('CSRF validation accepted using origin info.');
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return true;
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}
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126+
if ($this->acceptAsFallback) {
127+
$this->logger?->debug('CSRF validation accepted despite the absence of double-submit and origin info.');
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return true;
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}
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$this->logger?->debug('CSRF validation failed: double-submit and origin info not found.');
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return false;
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}
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public function clearCookie(Request $request, Response $response): void
138+
{
139+
$cookieName = ($request->isSecure() ? '__Host-' : '').$this->headerName;
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141+
if (!$request->cookies->has($cookieName)) {
142+
$response->headers->clearCookie($cookieName, '/', null, $request->isSecure(), false, 'strict');
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}
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}
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public function persistStrategy(Request $request): void
147+
{
148+
if ($request->hasSession(true) && $request->attributes->has($this->headerName)) {
149+
$request->getSession()->set($this->headerName, $request->attributes->get($this->headerName));
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}
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}
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public function onKernelResponse(ResponseEvent $event): void
154+
{
155+
if (!$event->isMainRequest()) {
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return;
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}
158+
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$this->clearCookie($event->getRequest(), $event->getResponse());
160+
$this->persistStrategy($event->getRequest());
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}
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/**
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* @return bool|null Whether the origin is valid, null if missing
165+
*/
166+
private function isValidOrigin(Request $request): ?bool
167+
{
168+
$source = $request->headers->get('Origin') ?? $request->headers->get('Referer') ?? 'null';
169+
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return 'null' === $source ? null : str_starts_with($source.'/', $request->getScheme().'://'.$request->getHttpHost().'/');
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}
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private function isValidDoubleSubmit(Request $request): bool
174+
{
175+
$token = $request->headers->get($this->headerName);
176+
177+
if (!\is_string($token) || \strlen($token) < 32) {
178+
return false;
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}
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181+
$cookieName = ($request->isSecure() ? '__Host-' : '').$this->headerName;
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return $request->cookies->get($cookieName) === $token;
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}
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}

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