cal.com (formerly cal.diy) suffers a repository takeover due to misconfigured GitHub Actions workflows. The pr.yml workflow triggers on pull_request_target, granting the workflow full write access to the repository and passing the credentials to the check-types.yml script, which performs a dangerous checkout of pull request code and executes it. This flaw, classified as CWE‑77, lets an attacker run arbitrary commands with the write‑scoped GITHUB_TOKEN, enabling commit pushes, merges, deletions, and force‑pushes of branches, effectively owning the repository.

All users of the cal.com platform, including those who host their own instance of cal.diy, are impacted. The vulnerable workflows reside in the main branch of the cal.com repository (referred to as cal.diy). No patched version has been released, so all deployments using the current workflow configuration remain exposed. Administrators should confirm the version of the repository and monitor for updates.

With a CVSS score of 8.5, the attack severity is high. The EPSS score is less than 1 %, suggesting a low but non‑zero chance of exploitation in the near term, and the vulnerability is not yet in the CISA KEV catalog. The typical attack path involves an authenticated contributor submitting a pull request: the workflow runs with the repository‑write token, the dangerous checkout pulls the attacker’s code, and the subsequent script installation and execution grant the attacker full control. Because the flaw lives in the workflow definition rather than a binary code path, the vulnerability can be exploited remotely from within the GitHub environment without any additional network access.