A cryptograhic flaw in Magento 2.1 prior to 2.1.18, Magento 2.2 prior to 2.2.9, Magento 2.3 prior to 2.3.2 could be abused by an unauthenticated user to discover an invariant used in gift card generation.
An unauthenticated user can execute SQL statements that allow arbitrary read access to the underlying database, which causes sensitive data leakage. This issue is fixed in Magento 2.1 prior to 2.1.18, Magento 2.2 prior to 2.2.9, Magento 2.3 prior to 2.3.2.
Magento Community Edition and Enterprise Edition before 2.0.10 and 2.1.x before 2.1.2 have XSS via e-mail templates that are mishandled during a preview, aka APPSEC-1503.