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/218f8015-e14b-46a8-889d-08b2b822f8ae