The Ninja Forms - Excel Export plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to, and including, 3.3.6 via the 'spreadsheetexportformid' parameter due to missing validation on a user controlled key. This makes it possible for authenticated attackers, with subscriber-level access and above, to enumerate any Ninja Forms form ID and download all stored submission data — including names, email addresses, phone numbers, physical addresses, and any other PII collected by site forms — as a downloadable XLSX file.