MathJax can rely on polyfill. Unfortunately, the polyfill service was taken over by a group of sketchy people. You can read more over here https://blog.cloudflare.com/polyfill-io-now-available-on-cdnjs-reduce-your-supply-chain-risk/

So, to avoid your visitors getting hacked, please replace all your https://polyfill.io links with:

https://cdnjs.cloudflare.com/polyfill