CVE-2026-84452

Case Description: MSRC 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). Finder Description: WARNING: Original content contained invalid characters. Please see original submission in the event that the characters removed are relevant for the PoC. serve/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. build 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. Reported Repro Steps: 1. Setup git clone -q https://github.com/microsoft/winml-cli.git ~/winml-poc && cd ~/winml-poc && mkdir -p temp /tmp/poc/evil/pwn python3 -m pip install -q --target /tmp/poc/deps onnx onnxruntime transformers fastapi uvicorn click 2. Hostile model repo (payload is module-level → runs on import) cat