Master Blocks 1.4.1 - 1.4.1.4 - Unauthenticated Stored XSS via White Label Settings

The Master Blocks WordPress plugin before 1.5.0 does not have authorisation on one of its REST routes, allowing unauthenticated users to update its settings, including a value that is output unescaped in the admin area, leading to Stored XSS that executes in the session of any administrator visiting a wp-admin page.