Excessive Data Exposure in Easy!Appointments Leads to Appointment Takeover

Executive Summary

CVE-2026-55651 is a vulnerability in the Easy!Appointments application, specifically in version 1.5.2. It is classified as an Excessive Data Exposure flaw in the customers search endpoint.

An authenticated user can exploit this vulnerability to obtain appointment hashes belonging to other users. These hashes allow the attacker to modify or delete appointments of other providers, leading to what is called an Appointments Takeover.

The issue arises due to a lack of proper object-level authorization controls, meaning the application does not restrict access to appointment data based on user permissions.

The vulnerability has a CVSS v3.1 BaseScore of 7.1, indicating high severity. It requires low attack complexity and low privileges to exploit.

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Detection Guidance

To detect this vulnerability on your network or system, you can check if your Easy!Appointments instance is running version 1.5.2, as this version is affected by the Excessive Data Exposure flaw in the customers search endpoint.

You can verify the installed version of Easy!Appointments by checking the application's configuration files or accessing the admin dashboard, which typically displays the version number.

• Check the application version via the command line if you have access to the server. Navigate to the Easy!Appointments installation directory and look for a version file or configuration file (e.g., config.php or version.txt). Example command: cat /path/to/easyappointments/config.php | grep 'APP_VERSION'.

To test for the vulnerability, you can attempt to access the /customers/search endpoint as an authenticated user and observe if it returns appointment hashes belonging to other users. This can be done using tools like curl or a web browser with developer tools enabled.

• Example curl command to test the endpoint (replace placeholders with actual values): curl -X GET 'http://your-easyappointments-instance/customers/search?keyword=test' -H 'Authorization: Bearer YOUR_AUTH_TOKEN'.

If the response includes appointment hashes or details that do not belong to the authenticated user, the system is likely vulnerable.

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Impact Analysis

If you are using Easy!Appointments version 1.5.2, this vulnerability could impact you in several ways.

• An attacker could access appointment hashes belonging to other users, compromising data confidentiality.
• The attacker could modify or delete appointments of other providers, leading to unauthorized cancellations or changes.
• This could disrupt service operations, causing confusion or financial loss for both providers and customers.
• The integrity of your appointment scheduling system could be compromised, affecting trust in the application.

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Compliance Impact

This vulnerability can have significant implications for compliance with standards and regulations like GDPR and HIPAA.

• GDPR: The exposure of appointment data, which may include personal or sensitive information, could violate GDPR's data protection principles. Unauthorized access to such data may lead to non-compliance with GDPR's requirements for data confidentiality and integrity, potentially resulting in fines or legal action.
• HIPAA: If the appointment data includes protected health information (PHI), this vulnerability could lead to unauthorized access or modification of PHI. This violates HIPAA's Privacy and Security Rules, which require safeguards to protect the confidentiality and integrity of PHI.

The lack of proper authorization controls may also indicate a failure to implement adequate security measures, which is a requirement under both GDPR and HIPAA.

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Mitigation Strategies

The most immediate step to mitigate this vulnerability is to upgrade Easy!Appointments to version 1.6.0 or later, as this version includes the fix for the Excessive Data Exposure issue.

• Download the latest version of Easy!Appointments from the official repository: https://github.com/alextselegidis/easyappointments/releases.
• Follow the upgrade instructions provided in the repository's documentation to ensure a smooth transition to the patched version.

If upgrading is not immediately possible, you can apply temporary mitigations by restricting access to the /customers/search endpoint.

• Modify the application code to enforce object-level authorization controls, ensuring that the /customers/search endpoint only returns appointments belonging to the requesting provider.
• Implement network-level restrictions, such as IP whitelisting or firewall rules, to limit access to the endpoint to trusted users only.

Monitor the application logs for any suspicious activity related to the /customers/search endpoint, such as repeated access attempts or unusual data retrieval patterns.

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