Executive brief
The Booking Calendar is a popular WordPress plugin used to manage appointment and event scheduling on websites. An attacker can craft a malicious link containing hidden code that, when clicked by a website visitor, injects and executes arbitrary scripts in their browser. This could allow account takeover, session hijacking, or theft of sensitive information from visitors. The vulnerability is particularly dangerous because it bypasses the plugin's security check by default, allowing anyone to exploit it without authentication.
Technical details
The vulnerability is a Reflected Cross-Site Scripting (XSS) flaw in the 'options' parameter of the Booking Calendar plugin. The root cause is insufficient input sanitization and output escaping in the vulnerable component. The nonce check is disabled by default (via the 'booking_is_nonce_at_front_end' option), allowing unauthenticated requests to reach the vulnerable code path. An attacker can craft a reflected XSS payload via a malicious URL; no user authentication is required, only social engineering to trick a user into clicking the link. Successful exploitation allows arbitrary JavaScript execution in the victim's browser within the context of the WordPress site, enabling session hijacking, credential theft, or malware injection. Patching to version 11.8.3 or later should resolve the issue.
Affected products
- Phonetic Brands Booking Calendar up to and including 11.8.2
Timeline
- 2026-09-18: disclosed