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.