CVE-2026-13358 in Simply Schedule Appointments Plugin
Summary
by MITRE • 08/16/2026
The Appointment Booking Calendar — Simply Schedule Appointments Booking Plugin plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to, and including, 1.6.12.10 via the ssa_past_appointments due to missing validation on a user controlled key. This makes it possible for authenticated attackers, with contributor-level access and above, to access appointment records belonging to arbitrary users and harvest the per-appointment ownership tokens (32-character hashes) embedded in the rendered HTML, which can then be used without any authentication to read or modify those appointments including full customer PII such as name, email, phone number, and private notes. The /wp-json/ssa/v1/render-shortcode REST endpoint is registered unconditionally on rest_api_init regardless of whether the Divi theme is installed, and its permission callback only requires current_user_can('edit_posts'), meaning any Contributor-level account is sufficient to trigger this entire exploit chain.
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Analysis
by VulDB Data Team • 08/16/2026
The vulnerability identified in the Appointment Booking Calendar plugin for WordPress represents a critical insecure direct object reference flaw that undermines fundamental access control mechanisms within the application. This issue affects all versions up to and including 1.6.12.10, where the plugin fails to properly validate user input when processing the ssa_past_appointments parameter. The flaw stems from insufficient validation of user-controlled keys, allowing authenticated attackers with contributor-level privileges or higher to manipulate the system's object references and gain unauthorized access to appointment records that belong to other users.
The technical implementation of this vulnerability occurs through the /wp-json/ssa/v1/render-shortcode REST endpoint which is registered unconditionally during the rest_api_init hook regardless of theme compatibility. This endpoint's permission callback mechanism only requires the relatively low-level capability of edit_posts, making it accessible to users who have contributor status or higher within the WordPress ecosystem. The vulnerability creates a complete breakdown in object isolation where an attacker can traverse the appointment data structure without proper authorization checks, effectively bypassing the intended security boundaries that should protect individual user appointment records from unauthorized access.
The operational impact of this vulnerability extends far beyond simple data exposure, as it enables comprehensive data harvesting and manipulation capabilities. Attackers can harvest 32-character hash tokens embedded within the rendered HTML output for each appointment, creating a complete set of ownership tokens that can be used to access and modify any target appointment without requiring additional authentication. This exploitation chain allows malicious actors to read and modify sensitive customer information including names, email addresses, phone numbers, and private notes, constituting a significant privacy breach that could lead to identity theft, spam campaigns, or other malicious activities. The vulnerability essentially transforms what should be a restricted user-specific data access mechanism into a universal appointment record harvesting tool.
The security implications align with CWE-284 (Improper Access Control) and represent a clear violation of the principle of least privilege in software design. From an attack perspective, this vulnerability maps directly to techniques described in the MITRE ATT&CK framework under privilege escalation and credential access domains, where attackers can leverage low-level permissions to gain broader system access capabilities. The exploit chain demonstrates how seemingly minor validation flaws can compound into major security incidents, particularly when combined with weak permission models that do not properly enforce user boundaries. Organizations using this plugin face significant risk of data breaches and regulatory violations, as the harvested PII could violate privacy regulations such as gdpr or ccpa requirements, making this vulnerability not just a technical concern but also a compliance and legal risk.
Mitigation strategies should prioritize immediate plugin updates to versions that address the validation flaw and implement proper access controls on REST endpoints. Security administrators should review user role assignments and consider implementing additional access restrictions for REST API endpoints that handle sensitive data. The remediation process must include validating all user inputs through robust sanitization techniques and ensuring that object references are properly validated against the authenticated user's ownership rights, preventing unauthorized cross-user data access patterns that this vulnerability enables.