CVE-2026-55651 Overview
CVE-2026-55651 is an Excessive Data Exposure vulnerability [CWE-200] affecting Easy!Appointments, a self-hosted appointment scheduling application. The flaw resides in the customers search endpoint of version 1.5.2. An authenticated user can query the endpoint and retrieve appointment hashes that belong to other users on the platform. Attackers can then use these hashes to modify or delete appointments owned by other providers, resulting in an appointment takeover. The maintainer resolved the issue in version 1.6.0.
Critical Impact
Authenticated attackers can enumerate appointment hashes of other providers through the customers search endpoint and use them to alter or delete arbitrary appointments across the scheduler.
Affected Products
- Easy!Appointments 1.5.2
- Earlier releases sharing the same customers search endpoint logic
- Self-hosted deployments not upgraded to 1.6.0
Discovery Timeline
- 2026-07-14 - CVE-2026-55651 published to NVD
- 2026-07-14 - Last updated in NVD database
Technical Details for CVE-2026-55651
Vulnerability Analysis
Easy!Appointments issues each appointment a hash that acts as a shared identifier for modification and deletion operations. The customers search endpoint returns customer records to authenticated users of the application. In version 1.5.2, the endpoint response includes appointment hashes linked to the returned customer objects rather than scoping the data to the requesting user. Any authenticated account can therefore retrieve hashes tied to appointments owned by other providers. Because the appointment modification and deletion routines authorize actions using the hash rather than the identity of the caller, possession of the hash is sufficient to control the appointment.
Root Cause
The root cause is over-broad response serialization in the customers search endpoint combined with hash-based authorization for appointment operations. The endpoint does not filter appointment-related fields based on the requester's ownership or role. Sensitive identifiers that should remain private are exposed to any authenticated client, breaking the trust model that assumes hashes are secrets known only to the appointment owner and their provider.
Attack Vector
The attack requires an authenticated session and network access to the application. An attacker queries the customers search endpoint, parses the response for appointment hashes belonging to other providers, and issues follow-up requests to the appointment modification or deletion endpoints using those hashes. No user interaction is required, and the scope remains within the vulnerable application. The result is unauthorized tampering with or destruction of third-party appointment data. Refer to the GitHub Security Advisory GHSA-4vmm-5qvc-w5p7 for maintainer details.
Detection Methods for CVE-2026-55651
Indicators of Compromise
- Unexpected PUT or DELETE requests against appointment endpoints originating from accounts that do not own the target appointments.
- Repeated authenticated GET requests to the customers search endpoint with broad query parameters returning large result sets.
- Appointment records modified or deleted without a corresponding audit entry from the owning provider account.
Detection Strategies
- Enable verbose application logging for the customers search endpoint and correlate response sizes with the requesting user's expected data scope.
- Alert when a single authenticated session accesses appointment hashes across multiple provider identifiers within a short time window.
- Compare appointment change events against the acting user's provider assignment to flag cross-tenant modifications.
Monitoring Recommendations
- Ingest Easy!Appointments web server and application logs into a centralized analytics platform to baseline normal endpoint usage.
- Monitor for anomalous ratios of read operations to appointment write operations per user account.
- Track authentication events tied to newly created low-privilege accounts followed by rapid queries to the customers search endpoint.
How to Mitigate CVE-2026-55651
Immediate Actions Required
- Upgrade all Easy!Appointments deployments from 1.5.2 to version 1.6.0 or later.
- Audit appointment records for unauthorized modifications or deletions performed since the vulnerable version was deployed.
- Rotate or invalidate outstanding appointment hashes where the application supports regeneration.
Patch Information
The maintainer released version 1.6.0, which fixes the excessive data exposure in the customers search endpoint. See the GitHub Security Advisory GHSA-4vmm-5qvc-w5p7 for the official patch reference and upgrade guidance.
Workarounds
- Restrict access to the Easy!Appointments backend to trusted networks or VPN clients until the upgrade is complete.
- Reduce the number of authenticated accounts and disable self-registration to limit exposure of the vulnerable endpoint.
- Place a reverse proxy or Web Application Firewall rule in front of the customers search endpoint to enforce per-role access controls.
# Upgrade Easy!Appointments to the patched release
git fetch --tags
git checkout 1.6.0
php composer.phar install --no-dev
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
