The polyfill.js is a popular open source library to support older browsers. 100K+ sites embed it using the cdn.polyfill.io domain. Notable users are JSTOR, Intuit and World Economic Forum. However, in February this year, a Chinese company bought the domain and the Github account. Since then, this domain was caught injecting malware on mobile devices via any site that embeds cdn.polyfill.io. Any complaints were quickly removed (archive here) from the Github repository.
You need to get up to date from three years ago. NodeJS 16.20, or thereabouts, enabled dependency auditing by default.
I’m still fighting my engineers go get current enough to use this (but we do have a proxy artifact server that also attempts to keep downloads clean, and a dependency scanner)