CVE-2026-91109

The Simply Schedule Appointments plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to, and including, 1.6.12.31 via the 'complete_group' parameter due to missing validation on a user controlled key. This makes it possible for authenticated attackers, with subscriber-level access and above, to disclose every co-booker's private per-appointment id_token (exposed as public_token) alongside their PII (name and email address), then use each leaked token to read, overwrite arbitrary appointment meta on, or cancel the co-booker's appointment via the same REST controller. Exploitation requires the attacker to possess a valid id_token for any single appointment within the targeted group booking.

• https://plugins.trac.wordpress.org/browser/simply-schedule-appointments/tags/1.6.12.27/includes/class-appointment-model.php#L1966
• https://plugins.trac.wordpress.org/browser/simply-schedule-appointments/tags/1.6.12.27/includes/class-appointment-model.php#L2315
• https://plugins.trac.wordpress.org/browser/simply-schedule-appointments/tags/1.6.12.27/includes/class-appointment-model.php#L3160
• https://plugins.trac.wordpress.org/browser/simply-schedule-appointments/tags/1.6.12.27/includes/class-db-model.php#L348
• https://plugins.trac.wordpress.org/changeset/3709365/simply-schedule-appointments/trunk/includes/class-appointment-model.php
• https://www.wordfence.com/threat-intel/vulnerabilities/id/d1cd3de2-16ca-4f95-ad6f-47cfbe00c959?source=cve