The GTN does not necessarily have a notion of 'supported versions' as our site is completely static and does not go through any sort of managed release cycle, unlike Galaxy. All dynamic features implemented in our site are strictly client-side, which generally provides acceptable security guarantees and low risk of user-facing exploitation.
There are occasionally vulnerabilities in the tools we use to build the site, however those vulnerabilities generally do not affect us, nor the output produced by jekyll and related tools.
Please report any vulnerabilities using GitHub private reporting. One of the maintainers will acknowledge your report within 5 business days (European).