The Keap Official Opt-in Forms WordPress plugin through 1.0.11 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/58f7c9aa-5e59-468f-aba9-b15e7942fd37/