Description

The Online Scheduling and Appointment Booking System WordPress plugin before 28.3 does not prevent deserialization of untrusted input and does not correctly restrict a privileged maintenance feature to administrators, allowing users granted a custom booking-management capability, which an administrator must explicitly assign, to inject arbitrary PHP objects, overwrite privileged site options, and read stored integration secrets.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "4.7",
  "pubDate": "2026-09-27T06:17:17.293Z",
  "pubdate": "2026-09-27T06:17:17.293Z",
  "executiveSummary": "The Online Scheduling and Appointment Booking System WordPress plugin prior to version 28.3 contains a critical security flaw involving insecure deserialization and improper access control.\nThe vulnerability allows authenticated users with specific booking-management capabilities to perform unauthorized actions, including the injection of arbitrary PHP objects and the modification of sensitive site options.\nBy manipulating the deserialization process, an attacker can bypass intended security restrictions, potentially leading to remote code execution, unauthorized access to system secrets, and full site compromise.\nThe flaw stems from the insufficient validation of user-supplied data passed to deserialization functions and the failure to restrict privileged maintenance features exclusively to site administrators.\nExploitation requires the attacker to hold an assigned booking-management capability, which is configurable by administrators. While this represents a specific privilege requirement, the impact is significant due to the ability to extract integration secrets and alter core configuration settings.\nThis vulnerability poses a high risk to the confidentiality, integrity, and availability of the affected WordPress installation.",
  "technicalDetails": "The vulnerability resides within the Online Scheduling and Appointment Booking System plugin's internal handling of user input during maintenance operations. The root cause is twofold: the use of unsafe PHP deserialization functions on untrusted input and an authorization flaw that incorrectly grants access to maintenance functionality.\nInsecure deserialization occurs when the plugin processes serialized objects from user-supplied parameters without proper sanitization or validation. PHP's unserialize() function, when utilized on untrusted data, allows an attacker to instantiate arbitrary objects existing within the application's scope or available via existing libraries. By crafting a malicious serialized payload, an attacker can trigger unintended object behaviors, such as magic method calls (e.g., __destruct, __wakeup), which can be chained to achieve object injection.\nThe authorization flaw exacerbates this issue by failing to implement strict capability checks for sensitive maintenance features. Although the plugin is intended to restrict certain functions to administrators, the current implementation allows users possessing a custom 'booking-management' capability to interact with these vulnerable endpoints. Because administrators can explicitly assign this capability to non-admin users, the attack surface is significantly broader than intended.\nThe attack flow proceeds as follows: First, an authenticated attacker with the booking-management capability identifies the vulnerable maintenance endpoint. Second, the attacker submits a specially crafted, serialized PHP object via the input vector. Third, the backend application unserializes this object, allowing the attacker to influence the internal state of the application. Through this object injection, the attacker can overwrite privileged site options stored in the database, effectively altering site configuration or settings.\nFurthermore, the ability to read stored integration secrets allows an attacker to compromise external services linked to the WordPress site, such as payment gateways or third-party scheduling APIs. Post-exploitation impact ranges from administrative configuration tampering to complete site takeover, as the ability to overwrite site options can often be leveraged to execute arbitrary code or redirect traffic to malicious servers.\nThe vulnerability affects all versions of the Online Scheduling and Appointment Booking System plugin released prior to version 28.3."
}