CVE-2025-13317 is a vulnerability classified under CWE-862 (Missing Authorization) found in the Appointment Booking Calendar plugin for WordPress, developed by codepeople. The flaw exists in all versions up to and including 1.3.96 and stems from an unauthenticated endpoint named cpabc_appointments_check_IPN_verification. This endpoint processes booking confirmations based on payment notifications but fails to verify the origin or authenticity of these notifications, nor does it enforce any authorization checks. Consequently, an unauthenticated attacker can craft requests with the 'cpabc_ipncheck' parameter to arbitrarily confirm bookings and insert them into the live calendar. This unauthorized insertion triggers administrative and customer notification emails, potentially causing confusion, operational disruption, and reputational harm. The vulnerability affects the integrity of booking data but does not compromise confidentiality or availability. The CVSS 3.1 base score is 5.3 (medium), reflecting the network attack vector, no required privileges or user interaction, and limited impact on integrity only. No patches or known exploits are currently reported, but the vulnerability is publicly disclosed and should be addressed promptly. The plugin is widely used by small and medium businesses for appointment scheduling, making this a relevant threat for organizations relying on this software for customer engagement and operational workflows.

For European organizations, this vulnerability primarily threatens the integrity of appointment booking data, allowing attackers to insert fraudulent bookings without authorization. This can disrupt business operations by causing scheduling conflicts, resource misallocation, and administrative overhead in managing false appointments. The automatic triggering of notification emails to administrators and customers can lead to confusion, customer dissatisfaction, and potential reputational damage. While confidentiality and availability are not directly impacted, the operational disruption and loss of trust can have significant business consequences, especially for service providers relying heavily on accurate scheduling (e.g., healthcare providers, salons, consultancy firms). Additionally, fraudulent bookings could be used as a vector for social engineering or further attacks if attackers leverage the notification system to deliver malicious content. The medium CVSS score reflects a moderate risk, but the ease of exploitation and lack of authentication requirements increase the urgency for mitigation. Organizations in Europe with a strong online appointment booking presence should consider this vulnerability a priority to address to maintain operational integrity and customer trust.

1. Immediately disable or restrict access to the cpabc_appointments_check_IPN_verification endpoint if possible, using web application firewalls (WAFs) or server configuration rules to block unauthenticated requests. 2. Implement strict authorization and authentication checks on the booking confirmation endpoint to ensure only legitimate payment notifications from trusted sources are processed. 3. Monitor booking logs and notification email triggers for unusual activity patterns, such as a sudden spike in confirmed bookings or notifications. 4. Employ network-level filtering to restrict access to the endpoint to known payment gateway IP addresses if feasible. 5. Engage with the plugin vendor or community to obtain patches or updates addressing this vulnerability and apply them promptly once available. 6. Educate administrative staff to verify suspicious bookings and establish manual verification processes temporarily. 7. Consider alternative booking plugins with verified security postures if patching is delayed or unavailable. 8. Regularly audit WordPress plugins for security updates and vulnerabilities to prevent similar issues.