The echosign plugin before 1.2 for WordPress has XSS via the inc.php page parameter.
https://wpvulndb.com/vulnerabilities/8465
https://wordpress.org/plugins/echosign/#developers
https://euvd.enisa.europa.eu/vulnerability/EUVD-2016-1975
https://0x62626262.wordpress.com/2016/04/21/echosign-plugin-for-wordpress-xss-vulnerability/