Open WebUI's Mass Assignment via Pydantic extra='allow' Allows Creating Folders in Other Users' Accounts

Mass Assignment via Pydantic extra='allow' Allows Creating Folders in Other Users' Accounts

Affected Component

Folder creation endpoint and form model:

• backend/open_webui/models/folders.py (lines 72-77, FolderForm with extra='allow')
• backend/open_webui/models/folders.py (lines 95-106, insert_new_folder dict construction)
• backend/open_webui/routers/folders.py (line 119, create_folder endpoint)

Affected Versions

Current main branch (commit 6fdd19bf1) and likely all versions since FolderForm adopted extra='allow'.

Description

FolderForm uses model_config = ConfigDict(extra='allow'), which permits arbitrary fields to pass through Pydantic validation and be included in model_dump(exclude_unset=True). In insert_new_folder, the server-assigned user_id is placed at the start of the dict and then overwritten by the spread of form data:

# models/folders.py:95-106
folder = FolderModel(
    **{
        'id': id,                                              # server
        'user_id': user_id,                                    # server — overwritten below
        **(form_data.model_dump(exclude_unset=True) or {}),    # user-controlled (extra='allow')
        'parent_id': parent_id,
        'created_at': int(time.time()),
        'updated_at': int(time.time()),
    }
)

Because FolderModel declares user_id: str as a real field (not just a form extra), any attacker-supplied user_id in the POST body is accepted by the model and persisted on the Folder row.

Attack Scenario

1. Attacker discovers a victim's user ID. User UUIDs commonly leak via the user search endpoint (GET /api/v1/users/search, intentionally accessible to verified users for sharing UI), shared chat metadata, or channel member lists.
2. Attacker sends:

   POST /api/v1/folders/
   {
     "name": "Important: Click here",
     "user_id": "<victim_user_id>",
     "meta": {"icon": "warning"},
     "data": {...}
   }

3. Pydantic accepts the extra user_id field (allowed by extra='allow').
4. insert_new_folder spreads the form data over the server-set 'user_id': user_id, overwriting it with the attacker's value.
5. The Folder row is persisted with user_id = <victim_user_id>.
6. The victim sees the attacker-planted folder in their UI on next load because GET /api/v1/folders/ filters by the viewer's own user_id.

The attacker can repeat this to plant multiple folders, use crafted name values for phishing ("Click here to recover account" / "Security alert"), and abuse the meta and data fields to add visual elements that further mimic legitimate content.

Impact

• Unauthorized write into victim's folder tree
• Phishing surface: attacker-controlled name, meta, and data render in the victim's UI in a trusted context
• DoS / spam: attacker can flood a victim with arbitrary folders; victim must manually delete each one
• Attacker cannot read the folder back — all read paths filter by the caller's own user_id — so confidentiality is preserved, but integrity and trust are compromised

Preconditions

• Attacker must have an authenticated account with features.folders permission (default for all users)
• Attacker must know or guess the victim's user UUID (obtainable through various non-sensitive endpoints)