The Web Invoice WordPress plugin through 2.1.3 does not properly sanitize and escape a parameter before using it in a SQL statement, leading to a SQL Injection exploitable by high privilege users such as admin by default. However, depending on the plugin configuration, other users, such as subscriber could exploit this as well
https://wpscan.com/vulnerability/45f43359-98c2-4447-b51b-2d466bad8261