Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to version 0.8.6, any authenticated user can overwrite any file's content by ID through the `POST /api/v1/retrieval/process/files/batch` endpoint. The endpoint performs no ownership check, so a regular user with read access to a shared knowledge base can obtain file UUIDs via `GET /api/v1/knowledge/{id}/files` and then overwrite those files, escalating from read to write. The overwritten content is served to the LLM via RAG, meaning the attacker controls what the model tells other users. Version 0.8.6 patches the issue.

Affected: PyPI: open-webui

### Summary

Any authenticated user can overwrite any file's content by ID through the `POST /api/v1/retrieval/process/files/batch` endpoint. The endpoint performs no ownership check, so a regular user with read access to a shared knowledge base can obtain file UUIDs via `GET /api/v1/knowledge/{id}/files` and then overwrite those files, escalating from read to write. The overwritten content is served to the LLM via RAG, meaning the attacker controls what the model tells other users.

### Details

The `process_files_batch()` function in `backend/open_webui/routers/retrieval.py` appears to be designed as an internal helper. The knowledge base router (`add_files_to_knowledge_batch()` in `knowledge.py`) imports and calls it directly after performing its own ownership and access control checks. The frontend never calls the retrieval route directly; all legitimate UI flows go through the knowledge base wrapper.

However, the function is also exposed as a standalone HTTP endpoint via `@router.post(...)`. This direct route only requires `get_verified_user` (any authenticated user) and performs no ownership check of its own:

```python for file in form_data.files: text_content = file.data.get("content", "") # attacker-controlled

file_updates.append(FileUpdateForm( hash=calculate_sha256_string(text_content), data={"content": text_content}, # written to DB ))

for file_update, file_result in zip(file_updates, file_results): Files.update_file…

Affected: PyPI: open-webui

### Summary

Any authenticated user can overwrite any file's content by ID through the `POST /api/v1/retrieval/process/files/batch` endpoint. The endpoint performs no ownership check, so a regular user with read access to a shared knowledge base can obtain file UUIDs via `GET /api/v1/knowledge/{id}/files` and then overwrite those files, escalating from read to write. The overwritten content is served to the LLM via RAG, meaning the attacker controls what the model tells other users.

### Details

The `process_files_batch()` function in `backend/open_webui/routers/retrieval.py` appears to be designed as an internal helper. The knowledge base router (`add_files_to_knowledge_batch()` in `knowledge.py`) imports and calls it directly after performing its own ownership and access control checks. The frontend never calls the retrieval route directly; all legitimate UI flows go through the knowledge base wrapper.

However, the function is also exposed as a standalone HTTP endpoint via `@router.post(...)`. This direct route only requires `get_verified_user` (any authenticated user) and performs no ownership check of its own:

```python for file in form_data.files: text_content = file.data.get("content", "") # attacker-controlled

file_updates.append(FileUpdateForm( hash=calculate_sha256_string(text_content), data={"content": text_content}, # written to DB ))

for file_update, file_result in zip(file_updates, file_results): Files.update_file…