The vulnerability in cal.com (cal.diy) arises from the use of the pull_request_target trigger in GitHub Actions workflows with default write permissions. The pr.yml workflow passes these permissions to check-types.yml, which uses the dangerous-git-checkout action to check out attacker-controlled pull request code and executes it via yarn install and package.json scripts. This allows an attacker to run arbitrary commands with the repository's write-scoped GITHUB_TOKEN, leading to repository takeover capabilities such as pushing commits, merging or mutating pull requests, commenting, and branch deletion or force-push. The main branch is affected, 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 enables them to push unauthorized commits, merge or alter pull requests, add or delete comments, and delete or force-push branches, effectively compromising the integrity and control of the repository.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, repository maintainers should avoid using pull_request_target triggers with write permissions that execute untrusted code. Restrict GitHub Actions workflows to use least privilege tokens and avoid executing code from untrusted pull requests. Consider disabling or modifying the affected workflows to prevent execution of attacker-controlled code.