CVE-2026-91109 croixhaug CVE debrief

Who should care

Defenders responsible for WordPress deployments using the Simply Schedule Appointments plugin, particularly those with subscriber-level access or above, should assess exposure and prioritize verification and updates to prevent potential exploitation.

Why it matters

CVE-2026-91109 is a medium-severity vulnerability in the Simply Schedule Appointments plugin for WordPress, allowing authenticated attackers to disclose sensitive appointment data and potentially manipulate appointments. Defenders should prioritize verification and updates to prevent exploitation.

• Disclosure of sensitive appointment data, including co-bookers' private per-appointment id_tokens and PII
• Potential unauthorized access to and manipulation of appointment data
• Read, overwrite, or cancellation of appointments by authenticated attackers
• Verification of plugin version and exposure of appointment data

Technical summary

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. The vulnerability exists in the 'complete_group' parameter due to missing validation on a user controlled key. This allows authenticated attackers with subscriber-level access and above to disclose co-bookers' private per-appointment id_tokens and PII, and use leaked tokens to read, overwrite, or cancel appointments.

Defensive priority

Defenders should prioritize verifying and updating the Simply Schedule Appointments plugin to a fixed version, assessing exposure of appointment data, and monitoring for potential exploitation attempts.

Recommended defensive actions

• Verify and update the Simply Schedule Appointments plugin to a fixed version
• Assess exposure of appointment data and potential impact on co-bookers
• Monitor for potential exploitation attempts and anomalous activity
• Implement additional security measures to protect appointment data and prevent unauthorized access
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, including its description, CVSS score, and affected versions. However, the exact versions that are fixed or the scope of affected deployments require further verification from the vendor or additional sources.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.