I've recently started using GitHub Actions and I was very disappointed to learn how few "native" actions there are. I don't want to introduce yet another avenue of third-party code via the GitHub Actions marketplace.
(Apart from having run actions, the only other actions I use are the upload/download-artifact ones to share binaries between jobs, and the matrix feature for parallelizing runs.)
But to be clear, the kind of vulnerability that the P0 issue is talking about is not necessarily from malicious actions. As the issue itself says, the vuln also happens from untrusted input being processed by a trusted action, like issues and PRs.
I played around with some actions wrt. commit signing and originally wrote a action a verify commit and tag signatures (in the way I need ;=) ). But now I plan to port it to a more general interface I can call from a GH action.
So I have a "run tests" action which just executes .github/run-tests, and it is up to the project-owner to write "make test" in that script, or whatever else they prefer.
It keeps things well-defined, and portable, but avoids the need to have project-specific workflows. I like being able to keep the same .yaml files in all my projects.
https://github.com/skx/github-action-tester
Similar thing for building and uploading artifacts, run ".github/build" and specify the glob-pattern for your artifacts:
I’m still a bit unclear how that could happen in practice thought. So the PR/Issue text would need to be written to stdout?
Yes. The issue title (the two actions the P0 issue talks about both do this) or the text, and same for PRs.
So interpreters like node/ruby/perl etc could execute the malicious stuff in the env variables. Are there any other cli tools that could do something dangerous?