CVE-2026-110381 in Simply Schedule Appointments Plugin
Summary
by MITRE • 10/15/2026
Authorization Bypass Through User-Controlled Key vulnerability in NSquared Simply Schedule Appointments simply-schedule-appointments allows Exploiting Incorrectly Configured Access Control Security Levels.This issue affects Simply Schedule Appointments: from n/a through 1.6.12.35.
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Analysis
by VulDB Data Team • 10/15/2026
The identified vulnerability represents a critical authorization bypass flaw within the NSquared Simply Schedule Appointments plugin, specifically affecting versions ranging from initial releases up to version 1.6.12.35. This security defect stems from an improper implementation of access control mechanisms where the application relies on user-controlled keys or identifiers to determine privilege levels without adequate validation against server-side authorization policies. In a secure architecture, access decisions must be enforced centrally based on verified session tokens and role-based attributes rather than trusting input parameters directly supplied by the client side. When this principle is violated, an attacker can manipulate these control variables to escalate privileges, effectively bypassing intended restrictions that should limit their actions to those appropriate for their authenticated user level.
From a technical perspective, this flaw aligns with CWE-284 Improper Access Control and more specifically CWE-639 Authorization Bypass Through User-Controlled Key. The vulnerability allows an attacker to modify specific parameters in HTTP requests or API calls that dictate which resources are being accessed or what actions can be performed. By altering these keys, the malicious actor can access administrative functions, view sensitive appointment data belonging to other users, or modify scheduling configurations without possessing the necessary permissions. This type of attack is particularly dangerous because it does not require authentication bypass in the traditional sense; rather, it exploits a logical error where the system trusts client-supplied identifiers as authoritative sources for authorization decisions.
The operational impact of this vulnerability is significant for any organization relying on Simply Schedule Appointments to manage bookings and user interactions. Unauthorized access could lead to the exposure of personally identifiable information contained within appointment records, including names, contact details, and potentially sensitive health or business data depending on the industry context. Furthermore, an attacker with elevated privileges gained through this flaw could disrupt service availability by deleting appointments, altering schedules, or injecting malicious content into public-facing booking forms. This undermines the integrity and confidentiality of the application’s core functionality, leading to potential regulatory compliance issues under frameworks such as GDPR or HIPAA if protected health information is compromised due to insufficient access controls.
In terms of threat modeling, this vulnerability maps directly to MITRE ATT&CK technique T1078 Valid Accounts, specifically within the context of privilege escalation and lateral movement where an attacker leverages valid but improperly constrained credentials to perform actions beyond their intended scope. The exploitation path typically involves intercepting network traffic using a proxy tool like Burp Suite or OWASP ZAP, identifying the specific parameter controlling access rights, and modifying its value to reference administrative resources or functions that are otherwise restricted. Successful exploitation requires only basic knowledge of web application architecture and does not necessitate complex reverse engineering efforts, making it accessible to low-skilled threat actors as well as automated scanning tools.
To mitigate this vulnerability, immediate action is required by upgrading the Simply Schedule Appointments plugin to a version later than 1.6.12.35 where these access control checks have been corrected. Developers must ensure that all authorization decisions are made server-side using secure session management and role-based access control models rather than relying on client-supplied identifiers. Implementing strict input validation, enforcing least privilege principles, and conducting regular security audits of authentication flows can prevent similar issues in the future. Additionally, organizations should deploy Web Application Firewalls configured to detect anomalous patterns in parameter manipulation and monitor logs for unauthorized attempts to access administrative endpoints using standard user credentials.