Summary

Broken Access Control in Tool Valves

Open WebUI supports function calling through "Tools". Function calling allows an LLM to reliably connect to external tools and interact with external APIs. Exemplary use-cases include connecting to an internal knowledge base, retrieving emails from an exchange server, or retrieving order data from a shop backend.

These interactions often require the LLM to authenticate against backend services using API keys specifically created for a technical (Open WebUI) user.

To simplify configuration and secret handling, Open WebUI implements "Valves" and "UserValves" that allow users and administrators to input dynamic details like API keys or configuration options.

Valves have the following distinction:

• Valves: Configurable by admins only.
• UserValves: Configurable by any user.

The Tool Valves endpoint does not properly restrict read access to the valve. This allows a low privileged user to access all data contained within the valve. In the worst case, this gives a low privileged "Member" user access to sensitive Tool data, such as API keys for third-party systems.

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Details

1) Broken Access Control in Tool Valves

The following steps can be performed to reproduce the vulnerability.

1. An administrator creates an Open WebUI Tool with a configured Valve.

<img width="1038" height="597" alt="image" src="https://github.com/user-attachments/assets/f79bdde9-18fa-49e4-a6c3-5077731f0815" />

2. The administrator configures the API key within the Tool Valve.

<img width="1039" height="446" alt="image" src="https://github.com/user-attachments/assets/d88d06b9-fc21-45e5-8142-d9f874601f87" />

3. A user with at least "Member" privileges logs into Open WebUI.

The following screenshot shows the user overview of the test instance:

<img width="908" height="354" alt="image" src="https://github.com/user-attachments/assets/40025151-418d-4912-8400-1e1a6e5cd4e4" />

The following screenshot illustrates...