The Ninja Forms WordPress plugin is vulnerable to sensitive information disclosure via the bulk_export_submissions function found in the ~/includes/Routes/Submissions.php file, in versions up to and including 3.5.7. This allows authenticated attackers to export all Ninja Forms submissions data via the /ninja-forms-submissions/export REST API which can include personally identifiable information.
The Ninja Forms WordPress plugin is vulnerable to arbitrary email sending via the trigger_email_action function found in the ~/includes/Routes/Submissions.php file, in versions up to and including 3.5.7. This allows authenticated attackers to send arbitrary emails from the affected server via the /ninja-forms-submissions/email-action REST API which can be used to socially engineer victims.
In the Ninja Forms Contact Form WordPress plugin before 3.4.34.1, low-level users, such as subscribers, were able to trigger the action, wp_ajax_nf_oauth, and retrieve the connection url needed to establish a connection. They could also retrieve the client_id for an already established OAuth connection.