The Build App Online plugin for WordPress is vulnerable to authentication bypass in versions up to, and including, 3.0.5. This is due to the 'eb_user_email_verification_key' default value is empty, and the not empty check is missing in the 'eb_user_email_verify' 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 id. This can only be exploited if the 'Email Verification' setting is enabled.