https://mathjax.rstudio.com/latest/MathJax.js points to MathJax 2.7.2.
MathJax 2.7.2 is affected by the following vulnerabilities:
https://nvd.nist.gov/vuln/detail/CVE-2018-1999024 (fixed by 2.7.4) https://nvd.nist.gov/vuln/detail/CVE-2023-39663 (still present in 2.7.9, disputed by vendor)
I recommend the site point to 2.7.9, which should be backwards compatible with 2.7.2. The next version after 2.7.9 is 3.0, which has many breaking changes.
2.7.9 can be found at https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.9/MathJax.min.js