When importing a form from JSON, if the field label or handle contained malicious content, the output wasn't correctly escaped when viewing a preview of what was to be imported. As imports are undertaking primarily by users who have themselves exported the form from one environment to another, and would require direct manipulation of the JSON export, this is marked as moderate. This vulnerability will not occur unless someone deliberately …
It is possible to inject malicious code into the HTML content of an email notification, which is then rendered on the preview. There is no issue when rendering the email via normal means (a delivered email). This would require access to the form's email notification settings.
Users with access to a form's settings can include malicious Twig code into fields that support Twig. These might be the Submission Title or the Success Message. This code will then be executed upon creating a submission, or rendering the text. This is listed as low-medium severity due to requiring control panel access to edit a form's settings.