nextcloud-server/apps/settings/lib/SetupChecks/ForwardedForHeaders.php

<?php

declare(strict_types=1);

/**
 * SPDX-FileCopyrightText: 2023 Nextcloud GmbH and Nextcloud contributors
 * SPDX-License-Identifier: AGPL-3.0-or-later
 */

namespace OCA\Settings\SetupChecks;

use OCP\IConfig;
use OCP\IL10N;
use OCP\IRequest;
use OCP\IURLGenerator;
use OCP\SetupCheck\ISetupCheck;
use OCP\SetupCheck\SetupResult;

class ForwardedForHeaders implements ISetupCheck {
	public function __construct(
		private IL10N $l10n,
		private IConfig $config,
		private IURLGenerator $urlGenerator,
		private IRequest $request,
	) {
	}

	public function getCategory(): string {
		return 'security';
	}

	public function getName(): string {
		return $this->l10n->t('Forwarded for headers');
	}

	public function run(): SetupResult {
		$trustedProxies = $this->config->getSystemValue('trusted_proxies', []);
		$remoteAddress = $this->request->getHeader('REMOTE_ADDR');
		$detectedRemoteAddress = $this->request->getRemoteAddress();

		if (!\is_array($trustedProxies)) {
			return SetupResult::error($this->l10n->t('Your "trusted_proxies" setting is not correctly set, it should be an array.'));
		}

		foreach ($trustedProxies as $proxy) {
			$addressParts = explode('/', $proxy, 2);
			if (filter_var($addressParts[0], FILTER_VALIDATE_IP) === false || !ctype_digit($addressParts[1] ?? '24')) {
				return SetupResult::error(
					$this->l10n->t('Your "trusted_proxies" setting is not correctly set, it should be an array of IP addresses - optionally with range in CIDR notation.'),
					$this->urlGenerator->linkToDocs('admin-reverse-proxy'),
				);
			}
		}

		if (($remoteAddress === '') && ($detectedRemoteAddress === '')) {
			if (\OC::$CLI) {
				/* We were called from CLI */
				return SetupResult::info($this->l10n->t('Your remote address could not be determined.'));
			} else {
				/* Should never happen */
				return SetupResult::error($this->l10n->t('Your remote address could not be determined.'));
			}
		}

		if (empty($trustedProxies) && $this->request->getHeader('X-Forwarded-Host') !== '') {
			return SetupResult::error(
				$this->l10n->t('The reverse proxy header configuration is incorrect. This is a security issue and can allow an attacker to spoof their IP address as visible to the Nextcloud.'),
				$this->urlGenerator->linkToDocs('admin-reverse-proxy')
			);
		}

		if (\in_array($remoteAddress, $trustedProxies, true) && ($remoteAddress !== '127.0.0.1')) {
			if ($remoteAddress !== $detectedRemoteAddress) {
				/* Remote address was successfuly fixed */
				return SetupResult::success($this->l10n->t('Your IP address was resolved as %s', [$detectedRemoteAddress]));
			} else {
				return SetupResult::warning(
					$this->l10n->t('The reverse proxy header configuration is incorrect, or you are accessing Nextcloud from a trusted proxy. If not, this is a security issue and can allow an attacker to spoof their IP address as visible to the Nextcloud.'),
					$this->urlGenerator->linkToDocs('admin-reverse-proxy')
				);
			}
		}

		/* Either not enabled or working correctly */
		return SetupResult::success();
	}
}