github-slug-action is a GitHub Action to expose slug value of GitHub environment variables inside of one's GitHub workflow. Starting in version 4.0.0` and prior to version 4.4.1, 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. This can be used to execute code on the GitHub runners and to exfiltrate any secrets one uses in the CI pipeline. A patched action is available in version 4.4.1. No workaround is available.

Affected: GitHub Actions: rlespinasse/github-slug-action

### 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](https://securitylab.github.com/research/github-actions-untrusted-input/) 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.