Harden-Runner

OIDC Configured but GitHub Actions Still Vulnerable: Megalodon and actions-cool Attacks Expose Runner Risks

Even after widespread adoption of OIDC for temporary cloud credentials in GitHub Actions, two major attacks in May 2026 demonstrated that the approach remains insufficient on its own. Attackers compromised actions-cool/issues-helper by substituting action tags to execute malicious commits that read Runner.Worker memory. The Megalodon campaign injected malicious workflows into 5,561 public repositories, harvesting environment variables, credential files, kubeconfig, SSH keys, and OIDC tokens. OIDC eliminates long-lived AWS_ACCESS_KEY_ID secrets but leaves short-lived tokens exposed inside the runner during job execution. Four mandatory protection layers are now required: strict cloud trust policies using StringEquals on the sub claim, job-level id-token: write permissions, outbound traffic controls such as Harden-Runner, and CODEOWNERS enforcement on .github/workflows/. GitHub Environments with mandatory reviewers add an essential human-approval gate that would have disrupted the Megalodon attack path.