WPUpper Share Buttons <= 3.51 - Cross-Site Request Forgery to Custom CSS Update

The WPUpper Share Buttons plugin for WordPress is vulnerable to Cross-Site Request Forgery in all versions up to, and including, 3.51. This is due to missing or incorrect nonce validation on the 'save_custom_css_request' function. This makes it possible for unauthenticated attackers to inject custom CSS to modify a site via a forged request granted they can trick a site administrator into performing an action such as clicking on a link.