| Package | Affected versions | Patched versions |
|---|---|---|
| open-webui | < 0.8.6 | 0.8.6 |
| open webui | < 0.8.6 | 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.
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:
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_by_id(id=file_result.file_id, form_data=file_update)
# ^^^ no ownership check
There is no verification that file.user_id == user.id before the write. Any authenticated user who knows a file UUID can overwrite that file.
How an attacker obtains file UUIDs:
Same as with read access, any user who can see a knowledge base can retrieve file IDs for every document in it via GET /api/v1/knowledge/{id}/files. In deployments where knowledge bases are shared across teams, this gives any regular user a list of valid targets.
Suggested fix: Add an ownership check before writing:
for file in form_data.files:
db_file = Files.get_file_by_id(file.id)
if not db_file or (db_file.user_id != user.id and user.role != "admin"):
file_errors.append(BatchProcessFilesResult(
file_id=file.id, status="failed",
error="Permission denied: not file owner",
))
continue
Classification:
Running one of these products? Scan your site to see whether it exposes a vulnerable version.
Scan my site freeTested on Open WebUI 0.8.3 using a default Docker configuration.
Prerequisites:
ghcr.io/open-webui/open-webui:main)Obtaining the file UUID (attacker):
GET /api/v1/knowledge/{kb_id}/files
This returns metadata for all files in the KB, including their UUIDs.
Exploit (attacker):
python3 poc_exploit.py --url http://<host>:3000 --file-id <target-file-uuid> -t <attacker-jwt>
The PoC script: poc_exploit.py
POST /api/v1/retrieval/process/files/batch with a canary payload containing a unique marker stringVerifying RAG poisoning:
After the overwrite, log in as any other user, start a chat with the poisoned knowledge base attached, and ask about the document. The model's response will include the attacker's canary string (BOLA-<marker>), confirming that attacker-controlled content reached the LLM and influenced the response.
No special tooling is required. The script uses only Python 3 standard library (urllib).
Who is affected: Any multi-user Open WebUI deployment where knowledge bases are shared. The attacker needs a valid account (any role) and a target file UUID, which is available through any knowledge base they have read access to.
What can happen:
The core issue is that a function designed as an internal helper is exposed as a public endpoint without its own authorization checks. A user with read-only access to a knowledge base can escalate to write access over any file in it.
The research and reporting related to this vulnerability was aided by the help of AI tools.