The cal.com (cal.diy) repository is vulnerable to a command injection and repository takeover via GitHub Actions workflows. Specifically, the pr.yml workflow uses the pull_request_target trigger with default write permissions, which are passed to check-types.yml. The check-types.yml workflow performs a checkout of attacker-controlled pull request code using the dangerous-git-checkout action and executes it through yarn install and package.json scripts. This execution occurs with the repository's write-scoped GITHUB_TOKEN, enabling an attacker to perform unauthorized repository modifications such as pushing commits, merging pull requests, and deleting branches. The vulnerability affects the main branch, and no official fix or patch has been released.

An attacker who submits a malicious pull request can execute arbitrary commands within the GitHub Actions environment with write permissions to the repository. This allows them to push commits, merge or alter pull requests, add or remove comments, and delete or force-push branches. Such actions can lead to full repository compromise, including unauthorized code changes and disruption of repository integrity.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is released, repository maintainers should avoid using the pull_request_target trigger with default write permissions for workflows that execute untrusted code. Restrict workflow permissions, avoid executing code from untrusted pull requests, and consider using safer workflow triggers or manual code reviews before merging. Monitor official cal.com advisories for updates and patches.