The malicious package includes a hidden _runtime directory containing a downloader and obfuscated JavaScript payload. The attack chain involves a Python script (start.py) that downloads and executes the Bun JavaScript runtime, which then runs an 11MB obfuscated malicious payload (router_runtime.js) to conduct credential theft. GitHub tokens are validated against api.github.com/user endpoint and used to inject worm-like payload to up to 50 branches. The malware implements npm-based propagation by modifying local npm packages with postinstall hooks, increasing patch version numbers, and repacking .tgz tarballs.