The Category Posts Widget WordPress plugin before 4.9.20 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).
https://wpscan.com/vulnerability/6bf93a34-a19f-4266-a95d-033551db43e6/