Open WebUI is an extensible, feature-rich, and user-friendly self-hosted AI platform. From 0.10.0 until 0.11.0, the DELETE /api/v1/folders/{id} handler in backend/open_webui/routers/folders.py allowed a user granted write access to a shared chat folder to permanently delete chats and messages belonging to the folder owner. The cascade following the authorization check is bound to the folder owner's id, but the subfolder check accepted any inherited write grant instead of requiring ownership or administrator status. A collaborator can destroy the owner's subtree or force-move chats out of it when delete_contents=false. This issue is fixed in 0.11.0.

Affected: PyPI: open-webui

## Summary A user granted write access to a shared chat folder could permanently delete chats and messages belonging to the folder's owner. Deleting a folder cascades into the owner's chats and the entire subfolder subtree, and the deletion handler required only write access on subfolders instead of ownership. Root folders were restricted to the owner or an admin, subfolders were not.

## Preconditions The Folders Sharing permission (`user.permissions.sharing.folders`) must be enabled; it is off by default. The victim must have shared a folder with the attacker at write access. `features.folders` and the `chat.delete` permission are enabled by default and are both required. Deployments that leave folder sharing disabled are not affected, and neither are single-user instances.

## Impact Permanent, irreversible destruction of another user's chat history within and beneath a shared folder. With `delete_contents=false` the same request instead force-moved the owner's chats out of the folder, an unauthorized relocation rather than a deletion. The write grant on the shared root folder is inherited by every descendant, so the attacker could destroy subfolders that were never explicitly shared with them. Nothing outside the shared folder's subtree is reachable, and no data is disclosed that write access did not already expose.

## Fix Fixed in 0.11.0 by https://github.com/open-webui/open-webui/pull/27003. Folder deletion is now restricted to the folder owner or an admin for root fo…

Affected: PyPI: open-webui

## Summary A user granted write access to a shared chat folder could permanently delete chats and messages belonging to the folder's owner. Deleting a folder cascades into the owner's chats and the entire subfolder subtree, and the deletion handler required only write access on subfolders instead of ownership. Root folders were restricted to the owner or an admin, subfolders were not.

## Preconditions The Folders Sharing permission (`user.permissions.sharing.folders`) must be enabled; it is off by default. The victim must have shared a folder with the attacker at write access. `features.folders` and the `chat.delete` permission are enabled by default and are both required. Deployments that leave folder sharing disabled are not affected, and neither are single-user instances.

## Impact Permanent, irreversible destruction of another user's chat history within and beneath a shared folder. With `delete_contents=false` the same request instead force-moved the owner's chats out of the folder, an unauthorized relocation rather than a deletion. The write grant on the shared root folder is inherited by every descendant, so the attacker could destroy subfolders that were never explicitly shared with them. Nothing outside the shared folder's subtree is reachable, and no data is disclosed that write access did not already expose.

## Fix Fixed in 0.11.0 by https://github.com/open-webui/open-webui/pull/27003. Folder deletion is now restricted to the folder owner or an admin for root fo…