Open WebUI: Forged model meta.knowledge allows cross-user file read and deletion
Summary
Open WebUI lets a user who can create, update, or import workspace models store arbitrary meta.knowledge entries on their model without checking whether they own or can read the referenced files. Open WebUI then treats meta.knowledge entries of type file as an authorization source in two places: the built-in view_file tool reads the file's extracted text, and has_access_to_file()'s model branch authorizes the file content and file delete endpoints. A malicious model owner can therefore attach another user's file ID to their model metadata and read or delete that private file.
Impact
Security boundary crossed: file confidentiality and integrity.
An authenticated attacker needs the workspace.models or workspace.models_import permission (or write access to an existing model) and a victim file ID. With those, for a file they do not own and cannot otherwise read, the attacker can:
- read the file's extracted text (up to
100000 characters per view_file call from file.data.content), - read the file's content via
GET /api/v1/files/{id}/content, and - delete the file via
DELETE /api/v1/files/{id}.
Root Cause
ModelMeta allows extra metadata fields and ModelForm accepts that metadata without a validator for meta.knowledge file access:
```python
# backend/open_webui/models/models.py
class ModelForm(BaseModel):
model_config = ConfigDict(extra='ignore')
id: str
base_model_id: Optional[str] = None
name: str
meta: ModelMeta
params: ModelParams
```
Model creation only checks the caller's model-workspace permission and then stores the form data:
```python
# backend/open_webui/routers/models.py
if user.role != 'admin' and not await has_permission(
user.id, 'workspace.models', request.app.state.config.USER_PERMISSIONS, db=db
):
raise HTTPException(...)
model = await Models.insert_new_model(form_data, user.id, db=db)
```
The insert sink persists the supplied meta:
```python
# backend/open_webui/models/models.py
result = Model(
**{
**form_data.model_dump(exclude={'access_grants'}),
'user_id': user_id,
...
}
)
```
When built-in tools are assembled, meta.knowledge is passed through as __model_knowledge__, and any file entry enables view_file:
```python
# backend/open_webui/utils/tools.py
model_knowledge = model.get('info', {}).get('meta', {}).get('knowledge', [])
...
knowledge_types = {item.get('type') for item in model_knowledge}
if 'file' in knowledge_types or 'collection' in knowledge_types:
builtin_functions.append(view_file)
```
view_file treats matching __model_knowledge__ file IDs as authorization, before has_access_to_file():
```python
# backend/open_webui/tools/builtin.py
if (
file.user_id != user_id
and user_role != 'admin'
and not any(
item.get('type') == 'file' and item.get('id') == file_id for item in (__model_knowledge__ or [])
)
and not await has_access_to_file(...)
):
return json.dumps({'error': 'File not found'})
```
The same forged meta.knowledge is also trusted outside the tool path. has_access_to_file() iterates the caller's accessible models and returns true when a model's meta.knowledge contains the requested file ID:
```python
# backend/open_webui/utils/access_control/files.py
for model in await Models.get_models_by_user_id(user.id, permission=access_type, db=db):
knowledge_items = getattr(model.meta, 'knowledge', None) or []
for item in knowledge_items:
if isinstance(item, dict) and item.get('type') == 'file' and item.get('id') == file.id:
return True
```
This branch is not restricted to read, so it also satisfies the write check that DELETE /api/v1/files/{id} performs. The same missing validation applies to the import path (POST /api/v1/models/import) and the update path, not only create.
PoC
```python
#!/usr/bin/env python3
"""
Verifier for forged model meta.knowledge file entries reaching builtin tools.
The proof executes:
- the real Models.insert_new_model() sink with a forged meta.knowledge entry
- the real builtin view_file() authorization branch
Fake DB/model adapters are used only to avoid requiring a live Open WebUI
server. The security-sensitive code under test is Open WebUI application code.
"""
from __future__ import annotations
import asyncio
import ast
import json
import os
import sys
import types
from pathlib import Path
from types import SimpleNamespace
REPO = Path(__file__).resolve().parents[1]
BUILTIN_TOOLS = REPO / "backend/open_webui/tools/builtin.py"
def prepare_imports() -> None:
sys.path.insert(0, str(REPO / "backend"))
os.environ["VECTOR_DB"] = "none"
class DummyTyper:
def command(self, *args, **kwargs):
return lambda fn: fn
sys.modules.setdefault(
"typer",
types.SimpleNamespace(
Typer=lambda *args, **kw
