The 404 to Start WordPress plugin through 1.6.1 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/ae44f2d8-a452-4310-b616-54d9519867eb