GHSA-q56x-g2fj-4rj6: ONNX: TOCTOU arbitrary file read/write in save_external_dat

The save_external_data method seems to include multiple issues introducing a local TOCTOU vulnerability, an arbitrary file read/write on any system. It potentially includes a path validation bypass on Windows systems. Regarding the TOCTOU, an attacker seems to be able to overwrite victim’s files via symlink following under the same privilege scope. The mentioned function can be found here: https://github.com/onnx/onnx/blob/main/onnx/external_data_helper.py#L188