Login with phone number < 1.7.27 - Authentication Bypass due to Missing Empty Value Check

Description

The Login with phone number plugin for WordPress is vulnerable to authentication bypass in versions up to, and including, 1.7.26. This is due to the 'activation_code' default value is empty, and the not empty check is missing in the 'lwp_ajax_register' function. This makes it possible for unauthenticated attackers to log in as any existing user on the site, such as an administrator, if they have access to the user email. The vulnerability is patched in version 1.7.26, but there is an issue in the patch that causes the entire function to not work, and this issue is fixed in version 1.7.27.