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<?php |
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declare(strict_types=1); |
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namespace DanBettles\Defence\Filter; |
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use DanBettles\Defence\Envelope; |
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use Symfony\Component\HttpFoundation\Request; |
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use function array_diff; |
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use function array_map; |
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use function implode; |
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use function is_string; |
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use function sprintf; |
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use function strtoupper; |
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use const false; |
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use const null; |
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use const true; |
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/** |
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* Using the Symfony request object it is possible to simulate exotic HTTP methods (e.g. `PUT`) by making a `POST` |
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* request and specifying the intended method in a special parameter or in a special header. |
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* |
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* We've seen requests that have tried to exploit this feature. It's an attack vector that's easy to detect, so we |
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* provided this simple filter, which will return `true` if the request-method override looks at all dodgy. |
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* |
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* The approach is very simple: if a request looks even vaguely dodgy then the filter will reject it, even if Symfony |
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* wouldn't touch it anyway. |
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*/ |
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class InvalidSymfonyHttpMethodOverrideFilter extends AbstractFilter |
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{ |
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/** |
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* @var string[] |
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*/ |
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public const VALID_METHODS = [ |
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Request::METHOD_HEAD, |
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Request::METHOD_GET, |
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Request::METHOD_POST, |
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Request::METHOD_PUT, |
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Request::METHOD_PATCH, |
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Request::METHOD_DELETE, |
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Request::METHOD_PURGE, |
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Request::METHOD_OPTIONS, |
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Request::METHOD_TRACE, |
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Request::METHOD_CONNECT, |
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]; |
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public function __invoke(Envelope $envelope): bool |
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{ |
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$request = $envelope->getRequest(); |
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$allMethodOverrides = [ |
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$request->headers->get('X-HTTP-METHOD-OVERRIDE'), |
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$request->request->get('_method'), |
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$request->query->get('_method'), |
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]; |
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$filteredMethodOverrides = []; |
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foreach ($allMethodOverrides as $methodOverride) { |
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if (null === $methodOverride) { |
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continue; |
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} |
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if (!is_string($methodOverride)) { |
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$this->envelopeAddLogEntry($envelope, 'The type of the request-method override is invalid'); |
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return true; |
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} |
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$filteredMethodOverrides[] = strtoupper($methodOverride); |
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} |
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if (!$filteredMethodOverrides) { |
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// Nothing at all to worry about |
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return false; |
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} |
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// (Request-method override present) |
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$invalidMethodOverrides = array_diff($filteredMethodOverrides, self::VALID_METHODS); |
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// Reject the request if any request-method override, found anywhere, is invalid |
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if (!empty($invalidMethodOverrides)) { |
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$this->envelopeAddLogEntry($envelope, sprintf( |
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'The request contains invalid request-method overrides: %s', |
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implode( |
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', ', |
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array_map(fn ($invalidMethod) => "`{$invalidMethod}`", $invalidMethodOverrides) |
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) |
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)); |
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return true; |
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} |
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// (Valid request-method override present) |
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// A request-method override should accompany only `POST` requests, so if the method is something else and an |
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// override is present then the request is suspicious |
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return Request::METHOD_POST !== $request->getRealMethod(); |
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} |
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} |
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danbettles /
defence
