CubeCart is an ecommerce software solution. Prior to version 6.5.11, a logic flaw exists in the newsletter subscription endpoint that allows an attacker to unsubscribe any user without their consent. By changing the value of the force_unsubscribe parameter in the POST request to 1, an attacker can force the removal of any valid subscriber’s email address. This issue has been patched in version 6.5.11.