PeproDev Ultimate Invoice <= 2.0.9 - Insecure Direct Object Reference to Unauthenticated Order Information Exposure

The PeproDev Ultimate Invoice plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to, and including, 2.0.9 via the invoicing viewer due to missing validation on a user controlled key. This makes it possible for unauthenticated attackers to view invoices for completed orders which can contain PII of users.