The plugin does not escape the postid parameter of pvc_stats shortcode, allowing users with a role as low as Contributor to perform Stored XSS attacks. A post made by a contributor would still have to be approved by an admin to have the XSS triggered in the frontend, however, higher privilege users, such as editor could exploit this without the need of approval, and even when the blog disallows the unfiltered_html capability.
[pvc_stats postid='a" style="animation-name:twentytwentyone-close-button-transition" onanimationend="alert(origin)']
[pvc_stats postid='a" onmouseover="alert(origin)']