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.

The WPUpper Share Buttons plugin for WordPress is vulnerable to unauthorized access of data when preparing sharing links for posts and pages in all versions up to, and including, 3.43. This makes it possible for unauthenticated attackers to obtain the contents of password protected posts and pages.

The WPUpper Share Buttons WordPress plugin through 3.42 does not sanitise and escape some of its settings, which could allow high privilege users such as admin to perform Stored Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed (for example in multisite setup).