Before version 2.7.21.1370b23 the Meshtastic firmware GitHub Actions workflow main_matrix.yml was triggered by pull_request_target. The workflow design allowed multiple jobs to checkout code from a pull request originating from an external contributor’s fork and execute that code with full repository secrets and an elevated GITHUB_TOKEN. No approval gate was in place. Pull requests from external users with author_association “NONE” automatically triggered CI. The workflow ran attacker‑controlled files directly from the fork checkout. This flaw could lead to supply‑chain compromise, self‑hosted runner compromise, or repository takeover. The vulnerability is distinct from the GHSA‑6mwm‑v2vv‑pp96 fix which addressed a command injection in the setup job; that fix moved the github.head_ref argument to an environment variable but did not prevent the fork‑checkout vulnerability. The patch in version 2.7.21.1370b23 rectifies this issue.

The affected product is the Meshtastic firmware repository maintained by the Meshtastic project. Versions older than 2.7.21.1370b23 are vulnerable, as the protection was added in that release. Anyone who relies on the legacy GitHub Actions workflow for building or deploying firmware, or who hosts the workflow in their own account, is impacted.

The CVSS score of 10 reflects a critical severity. The EPSS score of 1% indicates a very low injection probability but still non‑trivial. While the vulnerability is not listed in the CISA KEV catalog, the lack of an approval gate means a malicious pull request from an external contributor can automatically trigger the destructive workflow. Attackers can simply create a PR from a fork, and GitHub will run the workflow, checkout the attacker’s code, and execute it with full repository privileges. The result is immediate privilege escalation in the CI environment and significant supply‑chain risk.