The SpeedSize Image & Video AI-Optimizer plugin for WordPress is vulnerable to Cross-Site Request Forgery in all versions up to, and including, 1.5.1. This is due to missing or incorrect nonce validation on the 'speedsize_clear_css_cache_action' function. This makes it possible for unauthenticated attackers to clear the plugins cache via a forged request granted they can trick a site administrator into performing an action such as clicking on a link.