Reflected cross-site scripting in development mode handler in Vaadin 14, 15-19

URL encoding error in development mode handler in com.vaadin:flow-server versions 2.0.0 through 2.6.1 (Vaadin 14.0.0 through 14.6.1), 3.0.0 through 6.0.9 (Vaadin 15.0.0 through 19.0.8) allows local user to execute arbitrary JavaScript code by opening crafted URL in browser.