Prevented possible XSS via link attachments

This filters out potentially malicious javascript: or data: uri's coming
through to be attached to attachments.
Added tests to cover.

Thanks to Yassine ABOUKIR (@yassineaboukir on twitter) for reporting this
vulnerability.

app/Http/Controllers/AttachmentController.php

@@ -110,7 +110,7 @@ class AttachmentController extends Controller
         try {
             $this->validate($request, [
                 'attachment_edit_name' => 'required|string|min:1|max:255',
-                'attachment_edit_url' =>  'string|min:1|max:255'
+                'attachment_edit_url' =>  'string|min:1|max:255|safe_url'
             ]);
         } catch (ValidationException $exception) {
             return response()->view('attachments.manager-edit-form', array_merge($request->only(['attachment_edit_name', 'attachment_edit_url']), [
@@ -145,7 +145,7 @@ class AttachmentController extends Controller
             $this->validate($request, [
                 'attachment_link_uploaded_to' => 'required|integer|exists:pages,id',
                 'attachment_link_name' => 'required|string|min:1|max:255',
-                'attachment_link_url' =>  'required|string|min:1|max:255'
+                'attachment_link_url' =>  'required|string|min:1|max:255|safe_url'
             ]);
         } catch (ValidationException $exception) {
             return response()->view('attachments.manager-link-form', array_merge($request->only(['attachment_link_name', 'attachment_link_url']), [
@@ -161,7 +161,7 @@ class AttachmentController extends Controller
 
         $attachmentName = $request->get('attachment_link_name');
         $link = $request->get('attachment_link_url');
-        $attachment = $this->attachmentService->saveNewFromLink($attachmentName, $link, $pageId);
+        $attachment = $this->attachmentService->saveNewFromLink($attachmentName, $link, intval($pageId));
 
         return view('attachments.manager-link-form', [
             'pageId' => $pageId,

app/Providers/AppServiceProvider.php

@@ -43,6 +43,13 @@ class AppServiceProvider extends ServiceProvider
             return substr_count($uploadName, '.') < 2;
         });
 
+        Validator::extend('safe_url', function ($attribute, $value, $parameters, $validator) {
+            $cleanLinkName = strtolower(trim($value));
+            $isJs = strpos($cleanLinkName, 'javascript:') === 0;
+            $isData = strpos($cleanLinkName, 'data:') === 0;
+            return !$isJs && !$isData;
+        });
+
         // Custom blade view directives
         Blade::directive('icon', function ($expression) {
             return "<?php echo icon($expression); ?>";

app/Uploads/AttachmentService.php

@@ -88,12 +88,8 @@ class AttachmentService extends UploadService
 
     /**
      * Save a new File attachment from a given link and name.
-     * @param string $name
-     * @param string $link
-     * @param int $page_id
-     * @return Attachment
      */
-    public function saveNewFromLink($name, $link, $page_id)
+    public function saveNewFromLink(string $name, string $link, int $page_id): Attachment
     {
         $largestExistingOrder = Attachment::where('uploaded_to', '=', $page_id)->max('order');
         return Attachment::forceCreate([
@@ -123,13 +119,11 @@ class AttachmentService extends UploadService
 
     /**
      * Update the details of a file.
-     * @param Attachment $attachment
-     * @param $requestData
-     * @return Attachment
      */
-    public function updateFile(Attachment $attachment, $requestData)
+    public function updateFile(Attachment $attachment, array $requestData): Attachment
     {
         $attachment->name = $requestData['name'];
+
         if (isset($requestData['link']) && trim($requestData['link']) !== '') {
             $attachment->path = $requestData['link'];
             if (!$attachment->external) {
@@ -137,6 +131,7 @@ class AttachmentService extends UploadService
                 $attachment->external = true;
             }
         }
+
         $attachment->save();
         return $attachment;
     }

resources/lang/en/validation.php

@@ -90,6 +90,7 @@ return [
     'required_without'     => 'The :attribute field is required when :values is not present.',
     'required_without_all' => 'The :attribute field is required when none of :values are present.',
     'same'                 => 'The :attribute and :other must match.',
+    'safe_url'             => 'The provided link may not be safe.',
     'size'                 => [
         'numeric' => 'The :attribute must be :size.',
         'file'    => 'The :attribute must be :size kilobytes.',

tests/Uploads/AttachmentTest.php

@@ -3,39 +3,51 @@
 use BookStack\Uploads\Attachment;
 use BookStack\Entities\Page;
 use BookStack\Auth\Permissions\PermissionService;
+use BookStack\Uploads\AttachmentService;
+use Illuminate\Http\UploadedFile;
 use Tests\TestCase;
+use Tests\TestResponse;
 
 class AttachmentTest extends TestCase
 {
     /**
      * Get a test file that can be uploaded
-     * @param $fileName
-     * @return \Illuminate\Http\UploadedFile
      */
-    protected function getTestFile($fileName)
+    protected function getTestFile(string $fileName): UploadedFile
     {
-        return new \Illuminate\Http\UploadedFile(base_path('tests/test-data/test-file.txt'), $fileName, 'text/plain', 55, null, true);
+        return new UploadedFile(base_path('tests/test-data/test-file.txt'), $fileName, 'text/plain', 55, null, true);
     }
 
     /**
      * Uploads a file with the given name.
-     * @param $name
-     * @param int $uploadedTo
-     * @return \Illuminate\Foundation\Testing\TestResponse
      */
-    protected function uploadFile($name, $uploadedTo = 0)
+    protected function uploadFile(string $name, int $uploadedTo = 0): \Illuminate\Foundation\Testing\TestResponse
     {
         $file = $this->getTestFile($name);
         return $this->call('POST', '/attachments/upload', ['uploaded_to' => $uploadedTo], [], ['file' => $file], []);
     }
 
+    /**
+     * Create a new attachment
+     */
+    protected function createAttachment(Page $page): Attachment
+    {
+        $this->post('attachments/link', [
+            'attachment_link_url' => 'https://example.com',
+            'attachment_link_name' => 'Example Attachment Link',
+            'attachment_link_uploaded_to' => $page->id,
+        ]);
+
+        return Attachment::query()->latest()->first();
+    }
+
     /**
      * Delete all uploaded files.
      * To assist with cleanup.
      */
     protected function deleteUploads()
     {
-        $fileService = $this->app->make(\BookStack\Uploads\AttachmentService::class);
+        $fileService = $this->app->make(AttachmentService::class);
         foreach (Attachment::all() as $file) {
             $fileService->deleteFile($file);
         }
@@ -145,21 +157,14 @@ class AttachmentTest extends TestCase
         $page = Page::first();
         $this->asAdmin();
 
-        $this->call('POST', 'attachments/link', [
+        $attachment = $this->createAttachment($page);
-            'attachment_link_url' => 'https://example.com',
+        $update = $this->call('PUT', 'attachments/' . $attachment->id, [
-            'attachment_link_name' => 'Example Attachment Link',
-            'attachment_link_uploaded_to' => $page->id,
-        ]);
-
-        $attachmentId = Attachment::first()->id;
-
-        $update = $this->call('PUT', 'attachments/' . $attachmentId, [
             'attachment_edit_name' => 'My new attachment name',
             'attachment_edit_url' => 'https://test.example.com'
         ]);
 
         $expectedData = [
-            'id' => $attachmentId,
+            'id' => $attachment->id,
             'path' => 'https://test.example.com',
             'name' => 'My new attachment name',
             'uploaded_to' => $page->id
@@ -242,4 +247,45 @@ class AttachmentTest extends TestCase
 
         $this->deleteUploads();
     }
+
+    public function test_data_and_js_links_cannot_be_attached_to_a_page()
+    {
+        $page = Page::first();
+        $this->asAdmin();
+
+        $badLinks = [
+            'javascript:alert("bunny")',
+            ' javascript:alert("bunny")',
+            'JavaScript:alert("bunny")',
+            "\t\n\t\nJavaScript:alert(\"bunny\")",
+            "data:text/html;<a></a>",
+            "Data:text/html;<a></a>",
+            "Data:text/html;<a></a>",
+        ];
+
+        foreach ($badLinks as $badLink) {
+            $linkReq = $this->post('attachments/link', [
+                'attachment_link_url' => $badLink,
+                'attachment_link_name' => 'Example Attachment Link',
+                'attachment_link_uploaded_to' => $page->id,
+            ]);
+            $linkReq->assertStatus(422);
+            $this->assertDatabaseMissing('attachments', [
+                'path' => $badLink,
+            ]);
+        }
+
+        $attachment = $this->createAttachment($page);
+
+        foreach ($badLinks as $badLink) {
+            $linkReq = $this->put('attachments/' . $attachment->id, [
+                'attachment_edit_url' => $badLink,
+                'attachment_edit_name' => 'Example Attachment Link',
+            ]);
+            $linkReq->assertStatus(422);
+            $this->assertDatabaseMissing('attachments', [
+                'path' => $badLink,
+            ]);
+        }
+    }
 }