GitLab EE/CE 11.1 through 12.9 is vulnerable to parameter tampering on an upload feature that allows an unauthorized user to read content available under specific folders.
https://www.debian.org/security/2020/dsa-4691
https://about.gitlab.com/releases/categories/releases/
https://about.gitlab.com/releases/2020/03/26/security-release-12-dot-9-dot-1-released/