GitHub Actions Cache Poisoning

What Is Broken and Why

GitHub Actions caches are shared across workflow runs within a repository. When a privileged workflow (with access to secrets or write permissions) restores a cache without verifying its integrity, an attacker who can write to the cache — even via a low-privilege workflow — can plant malicious content that executes in the privileged context. Since GitHub's November 2025 cache policy change, entries exceeding 10 GB are evicted immediately (not via batch jobs), making it possible to force eviction of legitimate cache entries and replace them with poisoned ones within a single workflow run.

Key Signals