Impact

This action uses the github.head_ref parameter in an insecure way.

This vulnerability can be triggered by any user on GitHub on any workflow using the action on pull requests. They just need to create a pull request with a branch name, which can contain the attack payload. (Note that first-time PR requests will not be run - but the attacker can submit a valid PR before submitting an invalid PR). This can be used to execute code on the GitHub runners (potentially use it for crypto-mining, and waste your resources) and to exfiltrate any secrets you use in the CI pipeline.

Patches

Pass the variable as an environment variable and then use the environment variable instead of substituting it directly.

Patched action is available on tag v4, tag v4.4.1, and any tag beyond.

Workarounds

No workaround is available if impacted, please upgrade the version

ℹ️ v3 and v4 are compatibles.

References

Here is a set of blog posts by Github's security team explaining this issue.

Thanks

Thanks to the team of researchers from Purdue University, who are working on finding vulnerabilities in CI/CD configurations of open-source software. Their tool detected this security vulnerability.