Unauthorized Appointment Injection in Easy!Appointments

Executive Summary

CVE-2026-52839 is a vulnerability in Easy!Appointments, a self-hosted appointment scheduler, affecting versions prior to 1.6.0. The issue involves an authorization bypass in the appointment management system.

The vulnerability allows an authenticated provider to inject or reassign appointments into another provider's schedule. Specifically, the `appointments/store` and `appointments/update` endpoints do not verify that the `id_users_provider` parameter matches the current session's provider ID. This means a malicious provider can create new appointments for another provider or modify existing appointments to assign them to a different provider.

Additionally, the `store` endpoint has a write-before-crash bug. Even though the system crashes due to a type error after the unauthorized appointment is created, the appointment is already committed to the database. The attacker receives an error response, but the unauthorized appointment persists.

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Detection Guidance

Detecting this vulnerability requires checking for unauthorized appointments in provider schedules or verifying if the application enforces proper provider isolation in the appointments/store and appointments/update endpoints.

• Review application logs for unusual activity in the appointments/store or appointments/update endpoints, such as repeated failed attempts or unexpected appointment assignments.
• Manually test the endpoints by attempting to inject or reassign appointments with a provider ID that does not match the authenticated session. For example, use a tool like curl or Postman to send a POST request to the appointments/store endpoint with an id_users_provider value belonging to another provider.
• Check the database for appointments where the id_users_provider does not match the expected provider for the appointment, which may indicate unauthorized modifications.
• Verify the application version. If it is Easy!Appointments version 1.5.2 or earlier, it is vulnerable to this issue.

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Impact Analysis

If you are using Easy!Appointments versions 1.5.2 or earlier, this vulnerability could impact you in several ways:

• Unauthorized appointment injections: A malicious provider could add appointments to your schedule without your knowledge or consent, leading to scheduling conflicts or disruptions.
• Appointment reassignments: Existing appointments could be reassigned to other providers, causing confusion, missed appointments, or miscommunication with clients.
• Data integrity issues: The write-before-crash bug means unauthorized appointments may persist in the database even if the attacker receives an error, leading to inconsistent or unreliable scheduling data.
• Operational disruptions: The vulnerability could be exploited to manipulate schedules, potentially leading to overbooking, underutilization of resources, or other operational inefficiencies.

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Compliance Impact

This vulnerability could impact compliance with several standards and regulations, depending on the context in which Easy!Appointments is used:

• GDPR (General Data Protection Regulation): If the application processes personal data of EU citizens, unauthorized access or manipulation of appointment data could violate GDPR principles. Specifically, it may breach the integrity and confidentiality of personal data (Article 5(1)(f)) and fail to implement appropriate technical measures to ensure data security (Article 32).
• HIPAA (Health Insurance Portability and Accountability Act): If Easy!Appointments is used in a healthcare setting to manage patient appointments, this vulnerability could lead to unauthorized access or modification of protected health information (PHI). This would violate the HIPAA Security Rule, which requires safeguards to ensure the confidentiality, integrity, and availability of PHI.
• Other industry-specific regulations: Depending on the sector (e.g., finance, legal), similar data protection or privacy regulations may apply. Unauthorized access to or manipulation of sensitive scheduling data could result in non-compliance with these regulations.

To mitigate compliance risks, organizations should update to version 1.6.0 or later, which patches the vulnerability, and review their systems to ensure no unauthorized changes were made to appointment data.

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Mitigation Strategies

To mitigate this vulnerability, follow these immediate steps:

• Upgrade to Easy!Appointments version 1.6.0 or later, which patches the vulnerability by enforcing proper provider ID matching in the store() and update() endpoints.
• If upgrading is not immediately possible, apply a temporary fix by modifying the application code to enforce provider ID validation in the appointments/store and appointments/update endpoints. Ensure the id_users_provider parameter matches the current authenticated provider's session ID before processing the request.
• Monitor the appointments/store and appointments/update endpoints for suspicious activity, such as unauthorized appointment injections or reassignments.
• Review and audit existing appointments in the database to identify and remove any unauthorized entries that may have been injected by exploiting this vulnerability.
• Restrict access to the application's administrative interfaces to trusted users only, reducing the risk of exploitation by malicious insiders.

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