A flaw was discovered in the way Ansible templating was implemented in versions before 2.6.18, 2.7.12 and 2.8.2, causing the possibility of information disclosure through unexpected variable substitution. By taking advantage of unintended variable substitution the content of any variable may be disclosed.
https://access.redhat.com/errata/RHSA-2019:3744
https://access.redhat.com/errata/RHSA-2019:3789
https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2019-10156
https://github.com/ansible/ansible/pull/57188
https://lists.debian.org/debian-lts-announce/2019/09/msg00016.html
https://lists.debian.org/debian-lts-announce/2021/01/msg00023.html