ultimatemember/includes/core/class-register.php

<?php
namespace um\core;

// Exit if accessed directly
if ( ! defined( 'ABSPATH' ) ) exit;

if ( ! class_exists( 'Register' ) ) {
    class Register {

        function __construct(){

            add_action("um_after_register_fields",  array( $this, 'add_nonce' ) );
            add_action("um_submit_form_register", array( $this, 'verify_nonce'), 1, 1);
        }

        public function add_nonce(){
            wp_nonce_field( 'um_register_form' );
        }

        public function verify_nonce( $args ){
	        /**
	         * UM hook
	         *
	         * @type filter
	         * @title um_register_allow_nonce_verification
	         * @description Enable/DIsable nonce verification of registration
	         * @input_vars
	         * [{"var":"$allow_nonce","type":"bool","desc":"Enable nonce"}]
	         * @change_log
	         * ["Since: 2.0"]
	         * @usage
	         * <?php add_filter( 'um_register_allow_nonce_verification', 'function_name', 10, 1 ); ?>
	         * @example
	         * <?php
	         * add_filter( 'um_register_allow_nonce_verification', 'my_register_allow_nonce_verification', 10, 1 );
	         * function my_register_allow_nonce_verification( $allow_nonce ) {
	         *     // your code here
	         *     return $allow_nonce;
	         * }
	         * ?>
	         */
	        $allow_nonce_verification = apply_filters( "um_register_allow_nonce_verification", true );

            if( ! $allow_nonce_verification  ){
                return $args;
            }

            if ( ! wp_verify_nonce( $args['_wpnonce'], 'um_register_form' ) || empty( $args['_wpnonce'] ) || ! isset( $args['_wpnonce'] ) ) {
                wp_die('Invalid Nonce.');
            }

            return $args;
        }

    }
}