Redmine before 4.1.5 and 4.2.x before 4.2.3 may disclose the names of users on activity views due to an insufficient access filter.
https://www.redmine.org/projects/redmine/wiki/Security_Advisories
https://www.redmine.org/projects/redmine/wiki/Changelog_4_2#423-2021-10-10
https://www.redmine.org/projects/redmine/wiki/Changelog_4_1#415-2021-10-10
https://www.redmine.org/news/133
https://lists.debian.org/debian-lts-announce/2021/10/msg00013.html