CVE-2026-55651 is a high-severity (CVSS 7.1) Information Exposure vulnerability in alextselegidis/easyappointments. No vendor fix is recorded yet; mitigation options are listed below.
Easy!Appointments Vulnerable to Appointments Takeover via Excessive Data Exposure
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-55651.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-55651 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 396,257 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
alextselegidis/easyappointmentsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
Summary
An Excessive Data Exposure vulnerability in the customers search endpoint allows an authenticated user to obtain appointment hashes belonging to other users. Using these hashes, an attacker can modify or delete appointments of other providers, resulting in an Appointments Takeover.
Details
The customers search endpoint exposes excessive information, including appointment hashes, to any authenticated user without proper authorization checks. These hashes uniquely identify appointments that do not belong to the searching user.
By reusing the obtained hashes, an attacker can interact with appointment management endpoints, allowing the modification or deletion of third-party appointments.
The lack of object-level authorization controls leads to an Appointments Takeover, impacting data confidentiality and integrity.
Impact
This vulnerability allows an authenticated user to take control of appointments belonging to other users. By obtaining and reusing the exposed hashes, an attacker can view, modify, or delete appointments of other providers, compromising data integrity and confidentiality. This may result in unauthorized appointment cancellations or modifications, operational disruption of the service.
PoC
- Let's start by viewing an appointment with the provider “Jane Doe.”
- Now, with the provider “test test” (another provider), let's send the request to /customers/search, where we can verify that the customer “Joe Shmoe” is on the list. This makes it possible to extract the hash of the appointment associated with the user Jane Doe, because the response is returning excessive data.
- With this hash, we then go to the endpoint /calendar/reschedule/{hash} with the provider “test test,” where we can check some information about the appointment.
- By changing the provider to “test test,” it is possible to change the appointment provider.
- By saving, we can verify that the appointment is now in the “test test” provider, thus disappearing from the “John Doe” provider calendar.
Provider "test test" Calendar:
<img width="1916" height="879" alt="image" src="https://github.com/user-attachments/assets/77b9e11a-860f-4c08-847e-fa95c064710d" />Provider "John Doe" Calendar:
<img width="1917" height="880" alt="image" src="https://github.com/user-attachments/assets/d39566f5-a58c-4337-a781-0886faa83c12" />5.1. Since we have takeover the appointment, it is possible to cancel/delete it.
<img width="1486" height="736" alt="image" src="https://github.com/user-attachments/assets/2a87b9d0-1726-4fdc-af72-7ae9e20cc050" /> <img width="290" height="867" alt="image" src="https://github.com/user-attachments/assets/815b1df6-dfd4-437a-a2bd-e9b61832d5b0" />Recommendation
When making the POST request to the /customers/search endpoint, only return appointments that belong to the provider sending the request. This way, the provider does not have access to the random hash and cannot perform the takeover.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | alextselegidis/easyappointments | all versions | No fix |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for alextselegidis/easyappointments, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Remediation status
No patched version of alextselegidis/easyappointments has shipped for CVE-2026-55651 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them.
Frequently Asked Questions
Is CVE-2026-55651 in your dependencies?
Find it across Packagist, including transitive dependencies.