Gitlab::BackgroundMigration::RedactLinks was prepending
EE::Gitlab::BackgroundMigration::RedactLinks, while
EE::Gitlab::BackgroundMigration::RedactLinks was trying to include
Gitlab::BackgroundMigration::RedactLinks::Redactable. Ruby 2.5.3 failed
with an uninitialized constant
(https://gitlab.com/gitlab-org/gitlab-ee/-/jobs/118388511).
It's possible that user pastes accidentally also unsubscribe link
which is included in footer of notification emails. This unsubscribe
link contains personal token which attacker then use to act as the
original user (e.g. for sending comments under his/her identity).