The Issues API in Redmine before 2.6.8, 3.0.x before 3.0.6, and 3.1.x before 3.1.2 allows remote authenticated users to obtain sensitive information in changeset messages by leveraging permission to read issues with related changesets from other projects.
https://www.redmine.org/versions/105
https://www.redmine.org/projects/redmine/wiki/Changelog_3_1
https://www.redmine.org/projects/redmine/wiki/Changelog_3_0
https://www.redmine.org/issues/21136
https://github.com/redmine/redmine/commit/8d8f612fa368a72c56b63f7ce6b7e98cab9feb22