In the plugin, users with the contributor role and above can create a new Payment Form, however the Label and Help Text input fields were not getting sanitized properly. So it was possible to inject malicious content such as img tags, leading to a Stored Cross-Site Scripting issue which is triggered when the form will be edited, for example when an admin reviews it and could lead to privilege escalation.
Proof of Concept
Steps to reproduce:
1) Sign in with an Contributor Account
2) Create a Form and add <img src=x onerror=alert(1) /> to the Help Text or Field Label option of any field
3) The XSS will fire because of the live render. Discard this alert Box and post your Form for review
4) Sign in with your admin account and check the new form in the backend (like when reviewing it).
5) Observe the XSS