Hi, Renovate author/maintainer here. The affected repo has now been taken down, so I am writing this partly from memory, but I believe the scenario is: 1. An attacker had write access to the tj-actions/changed-files repo 2. The attacker chose to spoof a Renovate commit, in fact they spoofed the most recent commit in the same repo, which came from Renovate 3. Important: this spoofing of commits wasn't done to "trick"…
I'm not sure how this could exploited by just making a PR, unless you for some reason have secrets enabled for builds by unknown contributors, which obviously would be a mistake. Usually, only builds using secrets only run on certain branches which has a known contributor approving the code before it gets there.
> people mistakenly assume that git tags are immutable
If you're distributing a library on GitHub used by many other people/projects, then you really need to setup `protected branches` and `protected tags`, where you can prevent changes somewhat.