The plugin does not sanitise and escape some parameters before outputting them back in the response, leading to a Reflected Cross-Site Scripting which could be used against high privilege users such as admin
Make a logged in admin open a page with the following code (this requires the attacker to know/guess a list_id)
CPE | Name | Operator | Version |
---|---|---|---|
yikes-inc-easy-mailchimp-extender | lt | 6.8.8 |