WPCOM Member <= 1.7.16 - Authentication Bypass via Weak OTP

The WPCOM Member plugin for WordPress is vulnerable to authentication bypass via brute force in all versions up to, and including, 1.7.16. This is due to weak OTP (One-Time Password) generation using only 6 numeric digits combined with a 10-minute validity window and no rate limiting on verification attempts. This makes it possible for unauthenticated attackers to brute-force the verification code and authenticate as any user, including administrators, if they know the target's phone number, and the target does not notice or ignores the SMS notification with the OTP.