CVE-2026-39987 For Marimo 0.20.4 PoC

⚠️ This tool is intended for educational purposes and authorized security testing only. The creator is not responsible for any unauthorized or illegal use. Use at your own risk. ⚠️

Info:

CVE-2026-39987 is a critical pre-authentication Remote Code Execution (RCE) vulnerability in Marimo (versions prior to 0.23.0)

Why it works:

The /terminal/ws endpoint is exposed without any authentication.

inside: marimo/_server/api/endpoints/terminal.py

@router.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket) -> None:
    app_state = AppState(websocket)
    if app_state.mode != SessionMode.EDIT:
        await websocket.close(...)
        return
    if not supports_terminal():
        await websocket.close(...)
        return
    await websocket.accept()
    # further down..
    child_pid, fd = pty.fork()

As you can see there's no authentication check at all before it creates a PTY shell.

Example use of the tool:

python3 CVE-2026-39987.py example.com -c 'whoami'

if it gives nothing and the target uses SSL use the --max-wait and --any-ssl arg.

python3 CVE-2026-39987.py example.com -c 'whoami' --any-ssl --max-wait 5

there's also interactive mode

python3 CVE-2026-39987.py example.com -i --any-ssl

References:

1. https://nvd.nist.gov/vuln/detail/CVE-2026-39987
2. https://github.com/marimo-team/marimo/security/advisories/GHSA-2679-6mx9-h9xc
3. https://www.cve.org/CVERecord?id=CVE-2026-39987
4. https://github.com/marimo-team/marimo