File Server/Transport/Http/Middleware/DnsRebindingProtectionMiddleware.php

1:	<?php
2:
3:	declare(strict_types=1);
4:
5:	/**
6:	* This file is part of the Nexus MCP SDK package.
7:	*
8:	* (c) 2026 John Paul E. Balandan, CPA <paulbalandan@gmail.com>
9:	*
10:	* For the full copyright and license information, please view
11:	* the LICENSE file that was distributed with this source code.
12:	*/
13:
14:	namespace Nexus\Mcp\Server\Transport\Http\Middleware;
15:
16:	use Nexus\Mcp\Core\Http\HttpStatus;
17:	use Nexus\Mcp\Core\Schema\Error\InvalidRequestError;
18:	use Nexus\Mcp\Core\Schema\JsonRpc\JsonRpcErrorResponse;
19:	use Psr\Http\Message\ResponseFactoryInterface;
20:	use Psr\Http\Message\ResponseInterface;
21:	use Psr\Http\Message\ServerRequestInterface;
22:	use Psr\Http\Message\StreamFactoryInterface;
23:	use Psr\Http\Server\MiddlewareInterface;
24:	use Psr\Http\Server\RequestHandlerInterface;
25:
26:	/**
27:	* Guards the MCP endpoint against DNS rebinding by rejecting an unlisted `Origin` with an id-less JSON-RPC
28:	* error on HTTP 403.
29:	*/
30:	final readonly class DnsRebindingProtectionMiddleware implements MiddlewareInterface
31:	{
32:	/**
33:	* @var list<non-empty-string>
34:	*/
35:	private array $allowedOrigins;
36:
37:	/**
38:	* @var list<non-empty-string>
39:	*/
40:	private array $allowedHosts;
41:
42:	/**
43:	* @param list<non-empty-string> $allowedOrigins Origins permitted to reach the endpoint, or `['*']` to allow any
44:	* @param list<non-empty-string> $allowedHosts Hosts permitted to reach the endpoint (empty disables `Host` validation), or `['*']` to allow any
45:	*/
46:	public function __construct(
47:	array $allowedOrigins,
48:	array $allowedHosts,
49:	private ResponseFactoryInterface $responseFactory,
50:	private StreamFactoryInterface $streamFactory,
51:	) {
52:	$this->allowedOrigins = array_map(strtolower(...), $allowedOrigins);
53:	$this->allowedHosts = array_map(strtolower(...), $allowedHosts);
54:	}
55:
56:	#[\Override]
57:	public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
58:	{
59:	if (! $this->isHostAllowed($request)) {
60:	return $this->reject('The request Host is not allowed.');
61:	}
62:
63:	if (! $this->isOriginAllowed($request)) {
64:	return $this->reject('The request Origin is not allowed.');
65:	}
66:
67:	return $handler->handle($request);
68:	}
69:
70:	private function isHostAllowed(ServerRequestInterface $request): bool
71:	{
72:	if ([] === $this->allowedHosts) {
73:	return true;
74:	}
75:
76:	return $this->matches($request->getHeaderLine('Host'), $this->allowedHosts);
77:	}
78:
79:	private function isOriginAllowed(ServerRequestInterface $request): bool
80:	{
81:	if (! $request->hasHeader('Origin')) {
82:	return true;
83:	}
84:
85:	return $this->matches($request->getHeaderLine('Origin'), $this->allowedOrigins);
86:	}
87:
88:	/**
89:	* @param list<non-empty-string> $allowed
90:	*/
91:	private function matches(string $value, array $allowed): bool
92:	{
93:	return \in_array('*', $allowed, true) \|\| \in_array(strtolower($value), $allowed, true);
94:	}
95:
96:	/**
97:	* @param non-empty-string $message
98:	*/
99:	private function reject(string $message): ResponseInterface
100:	{
101:	$envelope = new JsonRpcErrorResponse(
102:	id: null,
103:	error: new InvalidRequestError(message: $message),
104:	);
105:
106:	return $this->responseFactory->createResponse(HttpStatus::Forbidden->value)
107:	->withHeader('Content-Type', 'application/json')
108:	->withBody($this->streamFactory->createStream(json_encode($envelope, \JSON_THROW_ON_ERROR)))
109:	;
110:	}
111:	}
112:

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