Description

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()),...
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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

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.

Attacker sends:

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

Pydantic accepts the extra user_id field (allowed by extra='allow').

insert_new_folder spreads the form data over the server-set 'user_id': user_id, overwriting it with the attacker's value.

The Folder row is persisted with user_id = <victim_user_id>.

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)

Mitigation

Aliases

References