[mceachen]

GitHub actions supports version numbers, version ranges, and even commit hashes.

[werrett]

Only commit hashes are safe. In this case the bad actor changed all of the version tags to point to their malicious commit. See https://github.com/tj-actions/changed-files/tags

All the tags point to commit `^0e58ed8` https://github.com/tj-actions/changed-files/commit/0e58ed867...

[frenchtoast8]

The version numbers aren't immutable, so an attacker can just update the versions to point to the compromised code, which is what happened here. Commit hashes are a great idea, but you still need to be careful: lots of people use bots like Renovate to update your pinned hashes whenever a new version is published, which runs into the same problem.

[marsovo]

I don't think that's exactly what happened here: the compromise created new tags but generally the tag consumption relies on semantic versioning

In other words: you specify version 44, the attacker creates 44.1, you're still hosed.

[BlackFingolfin]

No you literally can (and the attackers did) change version 44 (the tag for it) to point to a different compromised commmit

[marsovo]

Yes, you're right. I wasn't able to double-check as the repo was deleted at the time. That said, AIUI making the tags read-only would still often be vulnerable to semantic-version exploitation.