CVE-2025-25173 Overview
CVE-2025-25173 is a stored Cross-Site Scripting (XSS) vulnerability in the FasterThemes FastBook plugin for WordPress, also known as fastbook-responsive-appointment-booking-and-scheduling-system. The flaw affects all plugin versions up to and including 1.1. It is classified under CWE-79, Improper Neutralization of Input During Web Page Generation. An attacker can inject malicious script content that is persistently stored by the plugin and later rendered in the browsers of users who view affected pages. Successful exploitation requires user interaction but no authentication, and the scope is changed, meaning the impact crosses security boundaries within the WordPress site.
Critical Impact
Attackers can persist malicious JavaScript in the WordPress site that executes in administrator or visitor browsers, enabling session hijacking, credential theft, and content manipulation.
Affected Products
- FasterThemes FastBook plugin for WordPress
- FastBook responsive appointment booking and scheduling system
- All versions from n/a through 1.1
Discovery Timeline
- 2025-06-27 - CVE-2025-25173 published to NVD
- 2026-04-23 - Last updated in NVD database
Technical Details for CVE-2025-25173
Vulnerability Analysis
The vulnerability is a stored Cross-Site Scripting (XSS) flaw in the FastBook appointment booking plugin. The plugin fails to properly sanitize and encode user-supplied input before persisting it and later rendering it in web pages. When a victim loads a page containing the malicious payload, the attacker-controlled script executes in the browser context of the WordPress site.
Stored XSS in a booking plugin is attractive to attackers because submission forms are typically exposed to unauthenticated users. Booking entries are then reviewed by administrators or staff in the WordPress admin dashboard, providing a reliable path for the payload to reach a privileged session.
Root Cause
The plugin does not enforce output encoding or input sanitization on fields that accept user-supplied data submitted through booking and scheduling functionality. Input flows from the request handler into a database record and is later concatenated into HTML output without using WordPress escaping helpers such as esc_html(), esc_attr(), or wp_kses(). This omission allows raw HTML and <script> tags to survive the storage and rendering pipeline.
Attack Vector
An unauthenticated remote attacker submits a booking or scheduling request containing a crafted JavaScript payload in a vulnerable field. The payload is stored in the WordPress database. When an administrator or another user views the booking record in the admin panel or front-end output, the script executes. Attackers can use this access to exfiltrate session cookies, perform actions on behalf of the administrator, or pivot to plant a persistent backdoor in the site.
No verified proof-of-concept code is publicly listed. See the Patchstack WordPress Vulnerability advisory for additional technical context.
Detection Methods for CVE-2025-25173
Indicators of Compromise
- Booking records, customer names, comments, or notes containing <script>, onerror=, onload=, or javascript: substrings.
- Unexpected outbound requests from administrator browsers to attacker-controlled domains shortly after loading the bookings admin page.
- New or modified WordPress administrator accounts created without a corresponding legitimate login.
Detection Strategies
- Query the WordPress database tables used by the FastBook plugin for entries containing HTML tags or JavaScript event handlers.
- Inspect web server access logs for POST requests to FastBook booking endpoints carrying URL-encoded <script> payloads or unusual character sequences.
- Use a Content Security Policy (CSP) report-only directive to surface inline script execution originating from FastBook-rendered pages.
Monitoring Recommendations
- Monitor WordPress admin sessions for anomalous activity such as plugin installations, theme edits, or user role changes following access to booking pages.
- Alert on changes to wp_users and wp_usermeta that add administrator privileges.
- Track requests to wp-admin/admin-ajax.php with FastBook-related actions and review payload contents for HTML markup.
How to Mitigate CVE-2025-25173
Immediate Actions Required
- Identify all WordPress sites running the FastBook plugin and confirm the installed version is 1.1 or earlier.
- Deactivate the FastBook plugin until a patched version is verified and installed.
- Review existing booking entries and purge records containing HTML tags or JavaScript payloads.
- Rotate WordPress administrator passwords and invalidate active sessions if compromise is suspected.
Patch Information
No fixed version is identified in the NVD record at the time of publication. Affected versions are listed as n/a through <= 1.1. Refer to the Patchstack advisory for the latest vendor remediation status.
Workarounds
- Remove or deactivate the FastBook plugin until the vendor releases a patched build.
- Deploy a web application firewall (WAF) rule that blocks POST requests to FastBook endpoints containing HTML tags or script event handlers.
- Apply a strict Content Security Policy that disallows inline scripts on pages rendering booking data.
- Restrict access to the WordPress admin area by IP allowlist to reduce exposure of administrator sessions.
# Configuration example: disable the vulnerable plugin via WP-CLI
wp plugin deactivate fastbook-responsive-appointment-booking-and-scheduling-system
wp plugin delete fastbook-responsive-appointment-booking-and-scheduling-system
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
