Unauthorized Access to the Container Registry of other groups was discovered in GitLab Enterprise 12.0.0-pre. In other words, authenticated remote attackers can read Docker registries of other groups. When a legitimate user changes the path of a group, Docker registries are not adapted, leaving them in the old namespace. They are not protected and are available to all other users with no previous access to the repo.
https://atomic111.github.io/article/gitlab-Unauthorized-Access-to-Container-Registry