GitHub Actions Script Injection

What Is Broken and Why

GitHub Actions workflows interpolate context expressions like ${{ github.head_ref }} directly into shell run: steps at workflow parse time — before the shell executes. An attacker who controls the input (branch name, PR title, issue body, commit message) can inject arbitrary shell commands that execute with the workflow's token permissions. Even a read-only token becomes dangerous if it can be leveraged into cache poisoning, secret exfiltration via subsequent workflows, or SSRF to internal services.

Key Signals