CVE-2026-86475 Overview
CVE-2026-86475 affects the Appointment Hour Booking WordPress plugin in versions before 1.5.95. The plugin fails to validate each appointment in a booking submission against the capacity configured for its own slot. Unauthenticated visitors can exploit this flaw to reserve slots that are already fully booked, bypassing the plugin's business logic controls.
The vulnerability is classified as improper input validation [CWE-20] and stems from missing per-slot capacity checks during multi-appointment submissions. Because the flaw requires no authentication and can be triggered remotely, any public-facing WordPress site running a vulnerable version of the plugin is at risk of booking integrity issues.
Critical Impact
Unauthenticated attackers can overbook appointment slots, disrupting business scheduling and causing integrity loss for booking data.
Affected Products
- Appointment Hour Booking WordPress plugin versions prior to 1.5.95
- WordPress sites exposing booking submission endpoints from the affected plugin
- Any deployment relying on the plugin's slot capacity enforcement for scheduling integrity
Discovery Timeline
- 2026-09-16 - CVE-2026-86475 published to the National Vulnerability Database
- 2026-09-16 - Last updated in the NVD database
Technical Details for CVE-2026-86475
Vulnerability Analysis
The Appointment Hour Booking plugin allows a single booking submission to contain multiple appointments. The plugin validates capacity limits inconsistently across appointments within one submission. When multiple appointments target the same time slot, the plugin does not re-check the running capacity against the slot's configured maximum. This lets a submission consume more seats than the slot allows.
The issue is a business logic flaw rooted in improper input validation. The plugin trusts the submitted appointment set without enforcing per-slot capacity as an invariant. As a result, an unauthenticated visitor can occupy slots that should be closed to new bookings. The impact is limited to integrity of booking records, with no confidentiality or availability loss reported.
Root Cause
The root cause is missing validation logic that iterates every appointment in a submission and confirms the requested slot still has remaining capacity at the time of processing. Because the check is either absent or applied only to the first appointment, subsequent entries bypass the constraint. This is a classic input validation failure [CWE-20] applied to business logic.
Attack Vector
An unauthenticated attacker submits a crafted booking request to the plugin's public booking endpoint. The request contains one or more appointments targeting a slot that is already at or near capacity. The plugin accepts the submission and records the bookings, exceeding the configured slot limit. No user interaction, privileges, or special conditions are required beyond reaching the booking form.
See the WPScan Vulnerability Report for additional technical detail on the affected submission flow.
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Indicators of Compromise
- Booking records showing more reservations than the configured slot capacity permits
- Multiple appointments created from the same source IP address within a short window targeting a saturated slot
- Unexpected booking submissions containing several appointments for identical time slots
Detection Strategies
- Compare live booking counts per slot against the plugin's configured capacity and alert on any breach
- Review web server access logs for repeated POST requests to the plugin's booking submission endpoint from unauthenticated clients
- Correlate booking database entries with source metadata to identify anomalous multi-appointment submissions
Monitoring Recommendations
- Enable audit logging on the WordPress database tables used by the plugin to record booking creation events
- Instrument the booking submission endpoint with a Web Application Firewall (WAF) rule that flags submissions containing multiple appointments for the same slot
- Track plugin version inventory across WordPress deployments to identify hosts still running versions before 1.5.95
How to Mitigate CVE-2026-86475
Immediate Actions Required
- Upgrade the Appointment Hour Booking plugin to version 1.5.95 or later on all WordPress installations
- Audit existing booking records for slots that exceed their configured capacity and reconcile with affected customers
- Restrict access to the booking submission endpoint using rate limiting or CAPTCHA to reduce automated abuse
Patch Information
The vendor addressed CVE-2026-86475 in Appointment Hour Booking version 1.5.95. The patched release enforces per-slot capacity validation across every appointment in a booking submission. Administrators should apply the update through the WordPress plugin management interface. Refer to the WPScan Vulnerability Report for the vendor's fix reference.
Workarounds
- Temporarily disable the Appointment Hour Booking plugin on sites where patching cannot be applied immediately
- Configure a WAF rule to reject booking submissions containing multiple appointments targeting the same slot
- Manually review and remove overbooked appointments until the plugin can be updated to the fixed version
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
