During a security research I found an authenticated Stored XSS vulnerability. The name of the plugin is: Custom Share Buttons with Floating Sidebar, the version of the affected plugin: < 4.2
The plugin 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 when the unfiltered_html capability is disallowed.
Put the following payload in any of the Floating Sidebar > Share on xxxx (such as Share on Facebook) settings: " autofocus onfocus=alert(/XSS/)// and save The XSS will be triggered when viewing the plugin's settings again, as well as in the frontend when the Sidebar and the related Social Share button (tick the checkboxes in the General settings) are active All settings appear to also lack sanitisation and escaping
NIST CVSS SCORE: 4.8
Plugin has more than 10,000+ active installations.