diff --git a/lib/Controller/PublicFileHandlingController.php b/lib/Controller/PublicFileHandlingController.php
index 7af9a10..ed0a420 100644
--- a/lib/Controller/PublicFileHandlingController.php
+++ b/lib/Controller/PublicFileHandlingController.php
@@ -89,6 +89,10 @@ public function load($token) {
             return new DataResponse(['message' => $this->l->t('You are not authorized to open this share')], Http::STATUS_BAD_REQUEST);
         }
 
+        if (!$this->checkPermissions($share, \OCP\Constants::PERMISSION_READ)) {
+            return new DataResponse(['message' => $this->l->t('You are not authorized to open this share')], Http::STATUS_FORBIDDEN);
+        }
+
         try {
             $node = $share->getNode();
         } catch (NotFoundException $e) {
diff --git a/tests/Unit/Controller/PublicFileHandlingControllerTest.php b/tests/Unit/Controller/PublicFileHandlingControllerTest.php
new file mode 100644
index 0000000..1fba76e
--- /dev/null
+++ b/tests/Unit/Controller/PublicFileHandlingControllerTest.php
@@ -0,0 +1,79 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\Files_MindMap\Tests\Unit\Controller;
+
+use OCA\Files_MindMap\Controller\PublicFileHandlingController;
+use OCP\AppFramework\Http;
+use OCP\Constants;
+use OCP\Files\File;
+use OCP\Files\Folder;
+use OCP\IL10N;
+use OCP\IRequest;
+use OCP\ISession;
+use OCP\Share\IManager;
+use OCP\Share\IShare;
+use PHPUnit\Framework\MockObject\MockObject;
+use Psr\Log\LoggerInterface;
+use Test\TestCase;
+
+class PublicFileHandlingControllerTest extends TestCase {
+	private IManager&MockObject $shareManager;
+	private PublicFileHandlingController $controller;
+
+	protected function setUp(): void {
+		parent::setUp();
+
+		$request = $this->createMock(IRequest::class);
+		$request->method('getParam')->willReturnMap([
+			['dir', null, '/'],
+			['filename', null, 'secret.km'],
+		]);
+		$this->shareManager = $this->createMock(IManager::class);
+		$l10n = $this->createMock(IL10N::class);
+		$l10n->method('t')->willReturnArgument(0);
+
+		$this->controller = new PublicFileHandlingController(
+			'files_mindmap',
+			$request,
+			$l10n,
+			$this->createMock(LoggerInterface::class),
+			$this->shareManager,
+			$this->createMock(ISession::class),
+		);
+	}
+
+	public function testLoadFromFileDropShareIsRefused(): void {
+		$folder = $this->createMock(Folder::class);
+		$folder->expects($this->never())->method('get');
+		$this->mockShare(Constants::PERMISSION_CREATE, $folder);
+
+		$this->assertSame(Http::STATUS_FORBIDDEN, $this->controller->load('token')->getStatus());
+	}
+
+	public function testLoadFromReadableShare(): void {
+		$file = $this->createMock(File::class);
+		$file->method('getContent')->willReturn('{"root":{}}');
+		$folder = $this->createMock(Folder::class);
+		$folder->method('get')->with('/secret.km')->willReturn($file);
+		$this->mockShare(Constants::PERMISSION_READ, $folder);
+
+		$response = $this->controller->load('token');
+
+		$this->assertSame(Http::STATUS_OK, $response->getStatus());
+		$this->assertSame(base64_encode('{"root":{}}'), $response->getData()['filecontents']);
+	}
+
+	private function mockShare(int $permissions, Folder $node): void {
+		$share = $this->createMock(IShare::class);
+		$share->method('getPermissions')->willReturn($permissions);
+		$share->method('getNode')->willReturn($node);
+		$this->shareManager->method('getShareByToken')->willReturn($share);
+	}
+}
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
new file mode 100644
index 0000000..a65b0f3
--- /dev/null
+++ b/tests/bootstrap.php
@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+use OCP\App\IAppManager;
+use OCP\Server;
+
+define('PHPUNIT_RUN', 1);
+
+require_once __DIR__ . '/../../../lib/base.php';
+require_once __DIR__ . '/../../../tests/autoload.php';
+
+\OC::$composerAutoloader->addPsr4('OCA\\Files_MindMap\\Tests\\', __DIR__ . '/', true);
+
+Server::get(IAppManager::class)->loadApp('files_mindmap');
diff --git a/tests/phpunit.xml b/tests/phpunit.xml
new file mode 100644
index 0000000..0916df0
--- /dev/null
+++ b/tests/phpunit.xml
@@ -0,0 +1,12 @@
+<?xml version="1.0"?>
+<!--
+  - SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+  - SPDX-License-Identifier: AGPL-3.0-or-later
+-->
+<phpunit bootstrap="bootstrap.php">
+	<testsuites>
+		<testsuite name="unit">
+			<directory>Unit</directory>
+		</testsuite>
+	</testsuites>
+</phpunit>