reachy_mini Allows Unrestricted Upload of File with Dangerous Type

Summary

The Reachy Mini daemon exposes the “/api/media/sounds/upload” endpoint without authentication and file validation mechanisms.
An attacker can use this endpoint to upload malicious files into the file system that will propagate in future attacks.

Compromise Chain: Unauthenticated to Full Root Access

This issue is part of a full compromise chain allowing an unauthenticated user to gain root access on the Reachy’s operating system:

1. Unrestricted File Upload in Media Sounds Upload API <= current finding
2. Bluetooth Authentication Bypass
3. Bluetooth Directory Traversal

Description

The root cause of the issue is at the handler located in “src/daemon/app/routers/media.py” file at the “upload_sound” method:

@router.post("/sounds/upload")
async def upload_sound(
    file: UploadFile = File(...),
) -> dict[str, str]:
    """Upload a sound file to the daemon's temporary sound directory.
    The file is saved to ``/tmp/reachy_mini_sounds/<original_filename>``.
    If a file with the same name already exists it is overwritten.
    Returns:
        JSON with the absolute *path* of the saved file on the daemon.
    """
    if not file.filename:
        raise HTTPException(status_code=400, detail="Filename is required")
    # Reject path traversal
    filename = Path(file.filename).name
    if not filename or filename in (".", ".."):
        raise HTTPException(status_code=400, detail="Invalid filename")
    os.makedirs(SOUNDS_TMP_DIR, exist_ok=True)
    dest = os.path.join(SOUNDS_TMP_DIR, filename)
    content = await file.read()
    with open(dest, "wb") as f:
        f.write(content)
    return {"status": "ok", "path": dest}

This endpoint lacks multiple defence mechanisms:

1. No authentication mechanism.
2. No file extension validation.
3. No file content/size validation.

Additionally, the daemon is bound to the 0.0.0.0 network interfaces (a.k.a. all network interfaces) by default along with permissive CORS ( allow_origins=[“*”] ) meaning the following API endpoint is exposed to every network interface the daemon is connected to.

PoC

1. Start the daemon in simulation mode (command depends on the installed environment):

 .venv/bin/mjpython -m reachy_mini.daemon.app.main --sim --no-media

2. After that check that the media upload API endpoint is activated and you can upload a wav file:

curl -X POST http://<daemon_domain>:<daemon_port>/api/media/sounds/upload \
    -F "file=@/path/to/your/file.wav"

3. Now attempt to create a “.sh” file containing a script and upload it:

curl -X POST http://<daemon_domain>:<daemon_port>/api/media/sounds/upload \
    -F "file=@/path/to/your/script.sh"

4. Now error message will be received and you will see that the script file was successfully uploaded to disk.

Impact

Due to this issue, an attacker can upload malicious files instead of the intended sounds files, harming the integrity of the stored data and allowing an attacker to propagate a foothold in cases another vulnerabilities would arise.

Fix suggestion

Perform the following check on the API endpoint:

1. Validate that the file extension contains only desired extensions (allow-list approach).
2. Validate that the uploaded file’s content matches the desired extension (Magic numbers, and known file structure per file type).
3. Enforce authentication on the file upload endpoint.

Credit

The vulnerability was discovered by Natan Nehorai of the JFrog Vulnerability Research team.