Newsletter < 8.8.5 - Admin+ Stored XSS via Widget

The Newsletter WordPress plugin before 8.8.5 does not validate and escape some of its Widget options before outputting them back in a page/post where the block 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).