The AWeber WordPress plugin through 7.3.20 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/cc35b2f4-f1f1-4ed3-91b2-025bd5848b29/