In the Ninja Forms Contact Form WordPress plugin before 3.4.34.1, low-level users, such as subscribers, were able to trigger the action, wp_ajax_nf_oauth, and retrieve the connection url needed to establish a connection. They could also retrieve the client_id for an already established OAuth connection.
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.
The wp_ajax_nf_oauth_disconnect from the Ninja Forms Contact Form – The Drag and Drop Form Builder for WordPress WordPress plugin before 3.4.34 had no nonce protection making it possible for attackers to craft a request to disconnect a site's OAuth connection.