URL Redirection to Untrusted Site ('Open Redirect')
In the Ninja Forms Contact Form WordPress plugin before 3.4.34, the wp_ajax_nf_oauth_connect AJAX action was vulnerable to open redirect due to the use of a user supplied redirect parameter and no protection in place.
CWE-601 - Open Redirect
An open redirect attack employs a URL parameter, HTML refresh tags, or a DOM based location change to exploit the trust of a vulnerable domain to direct the users to a malicious website. The attack could lead to higher severity vulnerabilities such as unauthorized access control, account takeover, XSS, and more.