An issue has been discovered in GitLab CE/EE affecting all versions after 13.7 before 16.6.6, 16.7 prior to 16.7.4, and 16.8 prior to 16.8.1. Improper input sanitization of user name allows arbitrary API PUT requests.
https://about.gitlab.com/releases/2024/01/25/critical-security-release-gitlab-16-8-1-released/