The Category Posts Widget WordPress plugin before 4.9.18 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/119d5249-48e4-429e-8a1d-ad112e0c966d/