The Form Notify plugin for WordPress is vulnerable to Authentication Bypass in versions up to and including 1.1.10. This is due to the plugin trusting user-controlled cookie data to determine which WordPress account to authenticate after a LINE OAuth login. When LINE doesn't provide an email address (which is common), the plugin falls back to reading the 'form_notify_line_email' cookie value without verifying that the LINE account is associated with that email address.

This makes it possible for unauthenticated attackers to gain access to any user account on the site, including administrator accounts, by completing a LINE OAuth flow with their own LINE account while injecting a malicious cookie containing the target victim's email address.