Question

Your CI workflow builds and caches Node dependencies using a key derived from package-lock.json. The workflow triggers on both pull_request from forks and push to main. A security reviewer warns that a malicious contributor could poison the shared cache. What is the MOST accurate description of GitHub Actions cache scoping that mitigates this concern, and what remaining precaution is still required?

Accepted Answer

Caches created by a workflow run on a pull_request from a fork are written to a scope isolated to that PR's ref and cannot overwrite the base branch cache; you should still avoid restoring caches that could contain attacker-controlled build artifacts into privileged jobs.

Answer

All caches are globally shared across every branch and PR, so the only mitigation is to disable caching entirely for pull_request events.

Answer

Fork PR caches automatically overwrite the main branch cache under the same key, so you must add the run ID to every cache key to keep them unique.

Answer

Cache access is controlled solely by GITHUB_TOKEN permissions, so setting permissions: read-all fully prevents any cache poisoning from fork PRs.