Appointment Booking Plugin <= 5.7.2 - Unauthenticated Authentication Bypass to Customer Account Takeover via Insufficient Verification in create_wp_user_for_customer() username_exists FallbackCVE-2026-100163

The Appointment Booking Plugin – LatePoint | Calendar & Scheduling for WordPress plugin for WordPress is vulnerable to Authentication Bypass in versions up to, and including, 5.7.2 via the OsCustomerHelper::create_wp_user_for_customer() helper reached from the public process_step_customer() booking step. When the 'Use WordPress users as customers' option is enabled, the helper falls back from email_exists() to username_exists( $customer->email ), which matches any WordPress user whose user_login equals the victim customer's email even when that user's user_email is completely different, and links that WordPress user's ID into the victim's LatePoint customer row (only privileged roles are excluded; Subscriber is allowed). This makes it possible for authenticated attackers, with Subscriber-level access and above, to take over another customer's LatePoint account — accessing their bookings, service, agent, and calendar data, and having the victim customer's email overwritten with the attacker's on next login — by holding a Subscriber account whose user_login equals the victim's email and submitting an unauthenticated public booking step registration request.

Quoted source text, attributed separately from HOL analysis.