WP User Frontend < 4.3.14 - Reflected XSS via 'field_attr' Parameter

The User Frontend WordPress plugin before 4.3.14 does not sanitise and escape some user-supplied values before reflecting them into HTML attributes in a publicly reachable AJAX response, leading to Reflected Cross-Site Scripting. The affected action is gated by an anonymous nonce that only validates for logged-out requests, so the payload executes against logged-out visitors rather than authenticated users.