CVE-2026-87966 in Easy Appointments Plugin
Summary
by MITRE • 09/18/2026
The Easy Appointments WordPress plugin before 4.0.2.2 does not perform an ownership or authorization check on its unauthenticated appointment-reservation endpoint before updating an existing appointment identified by a request-supplied id, allowing unauthenticated attackers to overwrite, and through a follow-on cleanup delete, arbitrary appointments.
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Analysis
by VulDB Data Team • 09/18/2026
The vulnerability in the Easy Appointments WordPress plugin prior to version 4.0.2.2 represents a critical failure in access control mechanisms within an unauthenticated endpoint responsible for managing appointment reservations. This flaw allows any remote attacker who can interact with the application over the network to manipulate existing calendar data without providing valid credentials or session tokens. The core technical issue stems from the server-side logic failing to verify that the user initiating the request is the legitimate owner of the specific appointment identified by the supplied identifier. In a secure implementation, an update operation must validate that the requester has explicit permission to modify the resource in question, typically by cross-referencing the session identity with the ownership field stored in the database for that specific record. By omitting this check, the application treats any request containing a valid appointment ID as authorized, regardless of who is making it.
From an operational perspective, this lack of authorization enforcement leads to severe integrity violations within the scheduling system. An attacker can overwrite arbitrary appointments by submitting crafted requests with modified details such as time slots, service types, or customer information associated with existing entries. This capability disrupts business operations by corrupting schedules and potentially causing double-bookings or missed services for legitimate users. Furthermore, the vulnerability extends beyond simple modification due to a follow-on cleanup mechanism within the plugin's codebase. When certain conditions are met during an update operation, this logic may trigger deletion routines that remove appointments entirely. Consequently, attackers can not only alter but also permanently delete arbitrary calendar entries by exploiting the same unauthenticated endpoint, leading to significant data loss and service disruption for organizations relying on the platform for appointment management.
This vulnerability aligns with CWE-269, which describes Improper Privilege Control, specifically where a user is able to perform actions that exceed their assigned privileges due to insufficient authorization checks. It also maps directly to MITRE ATT&CK technique T1078, Valid Accounts, although in this specific case the exploitation does not require valid credentials at all, making it an unauthenticated attack vector often categorized under broader access control failures like CWE-284 Improper Access Control. The ability to overwrite and delete data without authentication places this flaw in a high-severity category due to its direct impact on data integrity and availability.
To mitigate this risk, administrators must immediately upgrade the Easy Appointments plugin to version 4.0.2.2 or later, where these authorization checks have been implemented to ensure that only authenticated users with proper ownership rights can modify appointment records. Until an update is applied, it may be necessary to restrict access to the affected endpoint through web application firewall rules if possible, although upgrading remains the definitive solution. Regular security audits and penetration testing of WordPress plugins are recommended to identify similar logic flaws in other components before they can be exploited by malicious actors seeking to disrupt business continuity or compromise sensitive scheduling data.