Simply Schedule Appointments - Security Vulnerability (CVE-2026-91109)

CVE-2026-91109

Vulnerability CVE-2026-91109 PLUGIN simply-schedule-appointments MEDIUM

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.

CVE-2026-91109

MEDIUM CVSS 6.5 Published 2026-10-01 Updated 2026-10-01

AI Risk Elevated (64/100) Active Exploit: No strong signal Published Exploit: No public exploit references Priority: P3 Priority

Severity Band MEDIUM

CVSS Vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

Affected Components 1

Reference Links 6

AI Risk Engine Elevated (64/100)

Exploitability High

Active Exploitation No strong signal

Published Exploit Status No public exploit references

Threat Timeline

2026-10-01 CVE published and first recorded in the threat feed.
2026-10-01 Record updated with latest vulnerability metadata.
2026-10-01 AI technical context refreshed for mitigation and impact guidance.
Now Monitoring for follow-up changes, linked references, and new related CVEs.

AI Context

Machine-generated threat intelligence

AI Updated 6 days ago

AI enriched 6 days ago (2026-10-01 18:41 UTC)

Technical Summary

Potential Impact

Severity is MEDIUM (CVSS 6.5). Depending on deployment context, affected components may be exposed to unauthorized actions or data integrity risk.

Exploitability Assessment

Exploitability is assessed as High based on remote code execution potential.

Primary risk drivers: remote code execution potential

Mitigation Recommendations

Validate affected product versions, prioritize patching, and monitor references for vendor remediation guidance. If immediate patching is not possible, apply compensating controls and limit exposure of vulnerable surfaces.

Detection & Monitoring

Track authentication anomalies, unexpected file writes, and suspicious plugin API activity around affected components.

Business Impact Lens

AI risk score 64/100 (Elevated, High) with priority P3 Priority. Prioritize remediation where affected components process customer data, admin sessions, or Internet-exposed workflows.

Affected Products

Simply Schedule Appointments PLUGIN · simply-schedule-appointments Affected range not specified Fixed version not specified

References

What to do about this

Patch on your next cycle Worth fixing, but not ahead of other work.

Fix it

Update Simply Schedule Appointments to the latest available version.

Where the vendor has not published a fix yet, disable the plugin until they do.

No Hack Halt control meaningfully contains this one — updating is the remedy. We would rather say so than sell you something that will not help.

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Am I affected by this vulnerability?

You are affected if your site runs Simply Schedule Appointments.

How do I fix it?

Update Simply Schedule Appointments to the latest available version. Where the vendor has not yet published a fix, remove or disable the plugin until they do.