GHSA-fq23-g58m-799r: Cross-site Scripting Vulnerability on Data Import
IntroductionThis write-up describes a vulnerability found in [Label Studio](https://github.com/HumanSignal/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](https://github.com/HumanSignal/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.DescriptionThe following [code snippet in Label Studio](https://github.com/HumanSignal/label-studio/blob/1.9.2.post0/label_studio/data_import/uploader.py#L125C5-L146) showed that is a URL passed the SSRF verification checks, the contents of the file would be downloaded using the filename in the URL.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](https://github.com/HumanSignal/label-studio/blob/1.9.2.post0/label_studio/data_import/api.py#L595C1-L616C62) 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.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 ConceptBelow were the steps to recreate this issue: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.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).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.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`.![xss-import-alert](https://user-images.githubusercontent.com/139727151/282223222-d8f9132c-838e-4aa6-9c03-a2bc83b4a409.png)ImpactExecuting 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 AdviceFor 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](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/sandbox)).Restrict the allowed file extensions that could be downloaded.DiscoveredAugust 2023, Alex Brown, elttam
CVSS v3.1: 4.7