CVE-2026-91109

Simply Schedule Appointments <= 1.6.12.31 - Insecure Direct Object Reference to Authenticated (Subscriber+) Sensitive Information Disclosure via 'complete_group' Parameter

2026-09-30 15:10
jtb75

Strategic Overview

Status
Patched in 1.6.12.33
Affected Plugin
Simply Schedule Appointments
Affected Version
<= 1.6.12.31
CVSS
6.5Medium
Weakness type
CWE-639 · Authorization Bypass Through User-Controlled Key
CVE
CVE-2026-91109
View all Simply Schedule Appointments vulnerabilities

At a glance

CVE-2026-91109 is a medium-severity Authorization Bypass Through User-Controlled Key vulnerability in the Simply Schedule Appointments WordPress plugin, affecting versions <= 1.6.12.31. It carries a CVSS score of 6.5 (reachable over the network; low attack complexity; high confidentiality impact). Exploitation requires an authenticated account at Subscriber level or above. The issue is fixed in version 1.6.12.33; sites on affected versions should update now. Disclosed September 2026, reported by jtb75.

Vulnerability Overview

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.

Technical Analysis

The vector marks this flaw as remotely reachable over the network, with low attack complexity — no special timing or configuration is needed, and no interaction from a victim user. A successful exploit has high impact on confidentiality.

CWE-639: Authorization Bypass Through User-Controlled Key

Simply Schedule Appointments <= 1.6.12.31 carries this weakness at complete_group, and reaching it takes an account at Subscriber level or above. Authorization bypass through a user-controlled key, often called insecure direct object reference, means the application looks up a record by an identifier from the request without checking that the caller owns it.

Changing a number in the request is enough to read or modify other users' records, which on commerce and membership sites means customer data. For Simply Schedule Appointments the fix is 1.6.12.33: builds <= 1.6.12.31 are affected, anything from 1.6.12.33 onward is not.

Remediation

Update to version 1.6.12.33, or a newer patched version

How does WordSec protect against this?

Because it turns on account access, WordSec's login security is the relevant layer: role-based two-factor, captcha and brute-force limits raise the cost of getting the account this needs. None of that substitutes for the fix: Simply Schedule Appointments 1.6.12.33 closes this, and updating the plugin is the step that ends it.

  • Login Security
  • Alerts

External References

https://www.cve.org/CVERecord?id=CVE-2026-91109https://www.wordfence.com/threat-intel/vulnerabilities/id/d1cd3de2-16ca-4f95-ad6f-47cfbe00c959https://nvd.nist.gov/vuln/detail/CVE-2026-91109

Related records

Vulnerability data © Defiant, Inc., provided under the Wordfence Intelligence T&C