The Classified Listing - Mobile Number Verification plugin for WordPress is vulnerable to Authentication Bypass in all versions up to, and including, 1.6.0. This is due to missing server-side Firebase OTP validation in the process_otp_login() function. This makes it possible for unauthenticated attackers to authenticate as any user with a phone number registered in the plugin's phone table by submitting an arbitrary OTP code and UID through the Firebase OTP login flow. Successful exploitation requires OTP login to be enabled with Firebase selected as the verification gateway, and requires the attacker to know or guess the target account's registered phone number. Administrator account takeover is possible if an administrator account has a phone number registered in the plugin.