The risk is simple enough. GitHub Enterprise allows admins to configure a list of actions to allow or deny. Ideally these actions are published in the GitHub Marketplace.

The idea is that the organization does not trust these third-parties, therefore they disable their access.

However this solution bypasses those lists by cloning open-source actions directly into the runner. At that point it’s just running code, no different from if the maintainers wrote a complex action themselves.