Falang multilanguage <= 1.3.39 - Cross-Site Request Forgery via add_language

The Falang multilanguage plugin for WordPress is vulnerable to Cross-Site Request Forgery in versions up to, and including, 1.3.39. This is due to missing or incorrect nonce validation on the add_language, update_language, and delete_language functions. This makes it possible for unauthenticated attackers to invoke those functions via a forged request granted they can trick a site administrator into performing an action such as clicking on a link.