The Expert Invoice WordPress plugin through 1.0.2 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/65d84e69-0548-4c7d-bcde-5777d72da555/