Open WebUI Exposes System Prompt to Regular User [Non-Admin]

Summary

A regular user [non-admin] can view the system prompt of the model which is set by an admin.

Details

When a regular user [non-admin] logs into the application, a http://IP:8080/api/models? web request is initiated by the application and in response, it reveals the system prompt of available models set by admin on models pages in workspace affecting the confidentiality of application

Affected System

Open WebUI v0.6.40 "main" branch

Vulnerability Details and Advisory from OWASP

LLM07:2025 System Prompt Leakage - https://genai.owasp.org/llmrisk/llm072025-system-prompt-leakage/

PoC

1. Regular User [Non-Admin] login on Open WebUI application. 2. A series of web requests get generated by the application, and the http://IP:8080/api/models? is also gets generated by application . 3. The response of http://IP:8080/api/models? web request reveals the system prompt of all the available models which is set is by the admin on models pages in workspace. <img width="940" height="352" alt="system prompt leak" src="https://github.com/user-attachments/assets/bd2c76f1-398f-4bc8-a8b2-5e14a768c560" />

Web Request

GET /api/models? HTTP/1.1 Host: localhost:8080 sec-ch-ua-platform: "Linux" authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6IjdmYjUxMmFhLTBmMTAtNDRkZi1iOWY1LThmNDg2MWFhNWFmOCIsImV4cCI6MTc2NjU2MjE5OH0.yJpavBynKItPQv76SMGKK012JIf29PVUv9sjuCDuRGQ Accept-Language: en-US,en;q=0.9 sec-ch-ua: "Chromium";v="141", "Not?A_Brand";v="8" sec-ch-ua-mobile: ?0 User-Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/141.0.0.0 Safari/537.36 Accept: application/json Content-Type: application/json Sec-Fetch-Site: same-origin Sec-Fetch-Mode: cors Sec-Fetch-Dest: empty Referer: http://localhost:8080/ Accept-Encoding: gzip, deflate, br Cookie: token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6IjdmYjUxMmFhLTBmMTAtNDRkZi1iOWY1LThmNDg2MWFhNWFmOCIsImV4cCI6MTc2NjU2MjE5OH0.yJpavBynKItPQv76SMGKK012JIf29PVUv9sjuCDuRGQ Connection: keep-alive

Impact

1. System prompts can reveal the model instructions, providing an attackers with inside knowledge about the system capabilities and bypass restrictions. 2. Attacker can perform content manipulation affecting the input/output of the model.

Details from MITRE ATLAS

Discover LLM System Information - https://atlas.mitre.org/techniques/AML.T0069 Discover LLM System Information: System Instruction Keywords - https://atlas.mitre.org/techniques/AML.T0069.001 Discover LLM System Information: System Prompt - https://atlas.mitre.org/techniques/AML.T0069.002

Recommendation

1. The web response should not reveal system prompt and related internal/back-end details regarding the model to the regular user. 2. Only the model name and non-sensitive details should be revealed to regular user and internal/back-end details should not be disclosed.