The TinyMCE Custom Styles WordPress plugin before 1.1.4 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/9afec4aa-1210-4c40-b566-64e37acf2b64