This, to me, isn't news. Any platform that permits free arbitrary code execution (so, Netlify, Cloudflare Pages, GitHub Actions, DockerHub automated builds, CircleCI, et al) that can access the network can be assumed to have been abused in this manner.
I think blocking network access is the simplest fix. Just make the payor specify a whitelist. Email them the blocked attempts. You can run the white list checker on a c3a.large for a pretty big CI.
I am of the school of know and manage your dependencies. And it is really hard to block stuff with a black list. Especially when the opponent has money.
