CVE-2026-45666: open-webui: IDOR exposes cross-user note data

### Summary The API /api/v1/notes/{note_id} endpoint lacks proper authorization checks, allowing authenticated users to retrieve notes belonging to other users by guessing or enumerating UUIDs. This results in unauthorized disclosure of potentially sensitive or private user data. ### Details - if notes is enabled from UI (Settings >> General >> Features >> Notes (Beta)) - From API, attacker can access other user notes - if notes is disabled from UI (Settings >> General >> Features >> Notes (Beta)) - Then attacker can enable the notes from /api/config and access other user notes ### PoC - Step 1: Log in to the application as a valid user (User A).  - Step 2: Intercept or inspect the response from the endpoint GET /api/config.  - Step 3: Observe the field "enable_notes": false in the JSON response. - Step 4: Manually change "enable_notes" to true using browser DevTools or by intercepting and modifying the response via a proxy like Burp Suite. (Please note, the occurrence of this API comes twice, hence modification needs to be made twice as well.)  - Step 5: Observe the loaded frontend application; the previously hidden notes form will now be visible.   - Step 6: Again, click on any note, intercept the request, and Replace the note_id in the URL with a different note ID known to belong to another user (e.g., by guessing or bruteforcing). - Step 7: Send the modified request while remaining logged in as User A. - Step 8: Observe that the server returns the content of another user's note, confirming unauthorized access.   ### Impact 1. Unauthorized access to user-created notes 2. Possible exposure of confidential or sensitive uploaded data 3. Violation of user privacy and data isolation 4. High risk of legal or compliance breaches in regulated environments ## Resolution Fixed in commit [de3317e26](https://github.com/open-webui/open-webui/commit/de3317e26bb67a2a7ea015a183bbd1d369880ebd), first released in **v0.8.11** (Mar 2026). All per-id note endpoints (`GET /api/v1/notes/{id}`, `POST /api/v1/notes/{id}/update`, `POST /api/v1/notes/{id}/access/update`, deletion) now enforce ownership: the handler fetches the note, then requires the caller to be admin, the note owner, or have an `AccessGrants` grant for the appropriate permission (`read` for retrieval, `write` for mutation). A non-owner with no grant receives 403. Users on `>= 0.8.11` are not affected.

An attacker with a low-privilege Open-WebUI account — for example, a contractor, intern, or external researcher with trial access — first checks /api/config via the browser developer tools and observes 'enable_notes': false. They intercept the config response with Burp Suite, flip the flag to true, and the Notes UI becomes visible in their session. They then click any note link in their own session to capture a sample UUID-formatted note_id from the GET /api/v1/notes/{id} request. From there, a simple script iterates through UUID variants (or uses knowledge of a target user's ID range) sending authenticated GET requests; each request that returns 200 instead of 403 reveals another user's private note. Across a 500-user enterprise instance, an attacker could exfiltrate the entire notes corpus within minutes, harvesting system prompt designs, pasted API keys, or confidential business data with no server-side resistance.