Netsparker detected frame injection, which occurs when a frame on a vulnerable web page displays another web page via a user-controllable input.
An attacker might use this vulnerability to redirect users to other malicious websites that are used for phishing and similar attacks. Additionally they might place a fake login form in the frame, which can be used to steal credentials from your users.
It should be noted that attackers can also abuse injected frames in order to circumvent certain client side security mechanisms. Developers might overwrite functions to make it harder for attackers to abuse a vulnerability.