The Category Posts Widget WordPress plugin before 4.9.17, term-and-category-based-posts-widget WordPress plugin before 4.9.13 does not validate and escape some of its "Category Posts" widget settings before outputting them back in a page/post where the Widget is embed, 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)
CWE-79