Magento Long Term Support (LTS) is an unofficial, community-driven project provides an alternative to the Magento Community Edition e-commerce platform with a high level of backward compatibility. Versions prior to 20.12.3 and 20.13.0 contain a vulnerability that allows script execution in the admin panel which could lead to cross-site scripting against authenticated admin users. The attack requires an admin user with configuration access, so in practicality it is not very likely to be useful given that a user with this level of access is probably already a full admin. Versions 20.12.3 and 20.13.0 contain a patch for the issue.
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.