Downloading malicious GitHub Actions workflow artifact results in path traversal vulnerability

Summary

A security vulnerability has been identified in GitHub CLI that could create or overwrite files in unintended directories when users download a malicious GitHub Actions workflow artifact through gh run download.

Details

This vulnerability stems from a GitHub Actions workflow artifact named .. when downloaded using gh run download. The artifact name and --dir flag are used to determine the artifact’s download path. When the artifact is named .., the resulting files within the artifact are extracted exactly 1 directory higher than the specified --dir flag value.

In 2.63.1, gh run download will not download artifacts named .. and . and instead exit with the following error message:

error downloading ..: would result in path traversal

Impact

Successful exploitation heightens the risk of local path traversal attack vectors exactly 1 directory higher than intended.

Remediation and Mitigation

1. Upgrade gh to 2.63.1
2. Implement additional validation to ensure artifact filenames do not contain potentially dangerous patterns, such as .., to prevent path traversal risks.