Gogs is an open source self-hosted Git service. Versions 0.13.4 and below have a broken access control vulnerability which allows authenticated users with write access to any repository to modify labels belonging to other repositories. The UpdateLabel function in the Web UI (internal/route/repo/issue.go) fails to verify that the label being modified belongs to the repository specified in the URL path, enabling cross-repository label tampering attacks. The vulnerability exists in the Web UI's label update endpoint POST /:username/:reponame/labels/edit. The handler function UpdateLabel uses an incorrect database query function that bypasses repository ownership validation. This issue has been fixed in version 0.14.1.