Gitea resolves local reusable workflow files from a fork's head commit when a trusted base-branch workflow runs for a pull_request_target event. A fork author can modify a referenced reusable workflow so attacker-controlled code executes with the repository and organization secrets available to that event. Exploitation requires a base workflow that calls a local reusable workflow, and bypasses the intended separation between trusted base code and untrusted fork code.
https://github.com/go-gitea/gitea/security/advisories/GHSA-r9ch-mqjm-g67v
https://github.com/go-gitea/gitea/releases/tag/v1.27.2
https://github.com/go-gitea/gitea/pull/38897
https://github.com/go-gitea/gitea/pull/38886