A path traversal vulnerability in onnx prior to version 1.21.0 allows an attacker to bypass symlink checks and read arbitrary files outside the intended model or user directory. This occurs because the symlink check uses std::filesystem::is_regular_file, which follows symlinks and thus can be bypassed. An attacker can craft a model with external data referencing a symlink to sensitive files, leading to unauthorized file reads when the model is loaded.