Appointment Booking Calendar <= 1.4.06 - Unauthenticated Payment Bypass via Insufficient PayPal IPN Verification
- ID
- WPSEC-2026-1774
- Plugin
- Appointment Booking Calendar (appointment-booking-calendar)
- Affected
- all versions before 1.4.07
- Remediation
- Update to 1.4.07 or later.
- CVSS 3.1
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
- Weakness
- CWE-345
- Usage
- Plugin Low · Affected versions None seen among sites WPSec scans, 2026-10-27
- Attack surface
- Appointment Booking Calendar on WPSec AttackSurface
- Fix released
- Published
Description
The Appointment Booking Calendar plugin for WordPress is vulnerable to payment bypass via the PayPal IPN handler (cpabc_ipncheck) in all versions up to, and including, 1.4.06, due to insufficient verification of payment notifications. The handler took the booking ID from the cpabc_ipncheck URL parameter, which is not part of the message PayPal verifies. It did not check the receiver e-mail, currency, amount or payment status (pending eCheck payments were accepted), and it did not stop a transaction ID from being used again. This makes it possible for unauthenticated attackers to mark arbitrary pending bookings as paid and confirmed, without paying the site owner, by sending a genuine PayPal-verified IPN message from an unrelated or minimal payment against any booking ID. Because the confirmation e-mail is also sent to the payer_email in that message, attackers can also receive other customers' booking details (name, e-mail, phone and comments).
References
- https://wpsec.com/vuln/WPSEC-2026-1774/
- https://plugins.svn.wordpress.org/appointment-booking-calendar/tags/1.4.07/
- https://wordpress.org/plugins/appointment-booking-calendar/
Published by WPSec. Provided as is, without warranty. Corrections: contact us.
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