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 requests from an unrecognised `Origin` or `Host`.
28:	*
29:	* A present-but-unlisted `Origin` is answered with an id-less JSON-RPC error on HTTP 403. A request without an
30:	* `Origin` header (non-browser clients) passes through, since only browsers send it. `Host` validation is a
31:	* beyond-spec, opt-in dimension: an empty allow-list disables it, otherwise the `Host` header must be present
32:	* and listed. Matching is case-insensitive, since RFC 9110 makes the scheme and host of a URI so.
33:	*/
34:	final readonly class DnsRebindingProtectionMiddleware implements MiddlewareInterface
35:	{
36:	private const string WILDCARD = '*';
37:
38:	/**
39:	* @var list<non-empty-string>
40:	*/
41:	private array $allowedOrigins;
42:
43:	/**
44:	* @var list<non-empty-string>
45:	*/
46:	private array $allowedHosts;
47:
48:	/**
49:	* @param list<non-empty-string> $allowedOrigins Origins permitted to reach the endpoint, or `['*']` to allow any
50:	* @param list<non-empty-string> $allowedHosts Hosts permitted to reach the endpoint (empty disables `Host` validation), or `['*']` to allow any
51:	*/
52:	public function __construct(
53:	array $allowedOrigins,
54:	array $allowedHosts,
55:	private ResponseFactoryInterface $responseFactory,
56:	private StreamFactoryInterface $streamFactory,
57:	) {
58:	$this->allowedOrigins = array_map(strtolower(...), $allowedOrigins);
59:	$this->allowedHosts = array_map(strtolower(...), $allowedHosts);
60:	}
61:
62:	#[\Override]
63:	public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
64:	{
65:	if (! $this->isHostAllowed($request)) {
66:	return $this->reject('The request Host is not allowed.');
67:	}
68:
69:	if (! $this->isOriginAllowed($request)) {
70:	return $this->reject('The request Origin is not allowed.');
71:	}
72:
73:	return $handler->handle($request);
74:	}
75:
76:	private function isHostAllowed(ServerRequestInterface $request): bool
77:	{
78:	if ([] === $this->allowedHosts) {
79:	return true;
80:	}
81:
82:	return self::matches($request->getHeaderLine('Host'), $this->allowedHosts);
83:	}
84:
85:	private function isOriginAllowed(ServerRequestInterface $request): bool
86:	{
87:	if (! $request->hasHeader('Origin')) {
88:	return true;
89:	}
90:
91:	return self::matches($request->getHeaderLine('Origin'), $this->allowedOrigins);
92:	}
93:
94:	/**
95:	* @param list<non-empty-string> $allowed
96:	*/
97:	private static function matches(string $value, array $allowed): bool
98:	{
99:	return \in_array(self::WILDCARD, $allowed, true)
100:	\|\| \in_array(strtolower($value), $allowed, true);
101:	}
102:
103:	private function reject(string $message): ResponseInterface
104:	{
105:	$envelope = new JsonRpcErrorResponse(
106:	id: null,
107:	error: new InvalidRequestError(message: $message),
108:	);
109:
110:	return $this->responseFactory->createResponse(HttpStatus::Forbidden->value)
111:	->withHeader('Content-Type', 'application/json')
112:	->withBody($this->streamFactory->createStream(json_encode($envelope, \JSON_THROW_ON_ERROR)))
113:	;
114:	}
115:	}
116:

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