Nom du plugin	Booking Calendar
Type of Vulnerability	Script intersite stocké (XSS stocké)
CVE Number	CVE-2025-9346
Urgence	Faible
CVE Publish Date	2025-08-27
Source URL	CVE-2025-9346

Booking Calendar <= 10.14.1 — Authenticated Stored Cross-Site Scripting (CVE-2025-9346)

A stored cross-site scripting (XSS) vulnerability was disclosed for the popular Booking Calendar WordPress plugin affecting versions up to and including 10.14.1. The vulnerability is tracked as CVE-2025-9346 and publicly reported on 27 August 2025. A fix was released in Booking Calendar 10.14.2.

As a managed WordPress Web Application Firewall vendor and security service provider, we want to give site owners, developers and hosting teams a clear, pragmatic walkthrough: what the vulnerability is, how it works, who it affects, possible attacker outcomes, how to detect exploitation attempts, and the defensive measures you should put in place immediately — both short-term mitigations and long-term hardening. We’ll also explain how WP-Firewall can protect your site while you apply fixes.

This article is written by our security engineers in plain, actionable language and includes recommended checks and safe code patterns to reduce risk.

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Executive summary (short)

• Vulnerability: Stored Cross-Site Scripting (XSS) in Booking Calendar plugin.
• Affected versions: Booking Calendar <= 10.14.1.
• Fixed in: 10.14.2.
• CVE: CVE-2025-9346.
• Privilege required to inject: an authenticated user with low-privilege account such as Contributor (or higher), depending on plugin configuration and site capabilities.
• Primary impact: Malicious script injected by an authenticated user gets stored and later rendered in administrative interfaces (or other pages), executing in the context of administrators or users who view the content.
• Severity: Medium/Low depending on context (public CVSS 5.9 was assigned), but remains a serious risk because it enables privilege escalation, account takeover, and post-exploitation persistence if chained with other issues.
• Immediate action: Update plugin to 10.14.2 as soon as possible. If you cannot update immediately, deploy WAF rules, restrict user roles, and audit stored booking entries for suspicious HTML/JS.

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What is Stored XSS and why it matters here

Stored XSS occurs when an application accepts user-supplied input, stores it (in the database or persistent storage), and later outputs that content without proper escaping or sanitization. When another user (often an administrator) views the stored content, the browser executes injected JavaScript under the context of the vulnerable site (origin). That script can steal session tokens, perform actions on behalf of the logged-in user, or load external malware.

In this Booking Calendar case the plugin accepts booking-related input from authenticated site users — booking notes, comments, guest details or custom fields — and later renders those inputs in the WordPress administration area or on pages where privileged users view booking entries. If sanitization wasn’t enforced at input or output, a malicious contributor could embed JavaScript that executes in the browser of whoever opens that booking record.

Why this is dangerous:

• An attacker with a Contributor account (a role often allowed on blogs/sites for user-contributed content) can inject persistent script.
• Administrators and other privileged users who regularly review bookings are high-value targets; executed script can perform actions as those users.
• Stored XSS is persistent and can be exploited at scale without continued attacker interaction.

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Technical analysis (how the vulnerability works)

Note: we will avoid publishing exploit code. The goal here is to explain mechanisms so defenders can detect and mitigate.

Typical vulnerable flow:

1. The plugin exposes a form or API endpoint which accepts booking metadata (guest name, email, comments, custom fields, notes).
2. Input is accepted from authenticated users (Contributor role or higher). The plugin fails to sanitize or properly escape HTML/JS in that field before storing it in the database.
3. Later, when viewing the booking record in the WordPress admin or a front-end output that is only accessible to authenticated users, the plugin outputs the stored value without escaping for HTML context (for example echoing raw text to the page).
4. The attacker’s script executes in the victim’s browser because the site origin is trusted — allowing actions like:
   • Reading cookies or session tokens (if not HttpOnly).
   • Submitting forms on behalf of the administrator.
   • Making authenticated AJAX calls to WordPress admin-ajax.php or REST endpoints.
   • Adding backdoors, modifying settings, or creating new admin users (via CSRF-like actions performed from the victim’s browser).
   • Displaying a phishing iframe or exfiltrating data to attacker-controlled endpoints.

Key technical issues that lead to exploitability:

• Lack of input validation on a field that accepts rich text or HTML.
• Lack of output escaping on rendering the stored field — the canonical mistake.
• Administrative views which render user content in full HTML context (e.g. innerHTML) are particularly dangerous.

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Affected components and versions

• Plugin: Booking Calendar (WordPress).
• Vulnerable versions: <= 10.14.1.
• Fixed in: 10.14.2.
• CVE: CVE-2025-9346.
• Published: 27 Aug 2025.
• Research credit: (public disclosure credited to the original researcher).

If you run any site using the Booking Calendar plugin and your installed plugin version is 10.14.1 or older, treat this as high-priority to address — especially if your site allows contributor-level accounts or guest bookings that create persistent records.

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Exploitation scenarios (realistic threats)

1. Contributor-to-admin escalation:
   • A site allows registered contributors to submit bookings with a notes field.
   • The contributor injects a script into the notes.
   • When an administrator opens the booking in the admin UI, the script performs an AJAX request to create a new administrator account or to change the site email and password reset flows.
2. Persistent front-end compromise:
   • If booking entries are displayed on a page where privileged editors or authors visit, the stored script could run in their session too.
   • Exploits could be chained to install persistent backdoors, plugins, or modify theme code.
3. Mass-targeting editorial teams:
   • A compromised booking entry could redirect admin users to a phishing page that looks like a plugin updater — convincing an admin to input credentials or install malicious code.
4. Third-party integrations:
   • If the booking content is used in email previews or dashboards that render HTML, the script could attempt to exfiltrate data or cause other systems to make requests.

Important context: the attacker must have a user account on the site (Contributor+). However, many sites allow self-registration or guest submitters; where those are available, the barrier to entry is low.

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Detection: signs you may be affected

Check for these indicators:

• Plugin version <= 10.14.1 in your site’s Plugins list.
• Presence of unexpected JavaScript-like strings stored in booking-related DB tables (look for "<script", "onmouseover=", "javascript:", "eval(", "innerHTML", "document.cookie", or obfuscated payloads).
• Unusual admin activity after a particular booking record was viewed (e.g., settings changed, new users created, posts modified).
• Suspicious outbound HTTP requests from the server to external domains, especially soon after admin users viewed a booking entry.
• Browser console errors or network activity initiated when opening booking admin pages.
• WAF logs showing attempts to inject script code via POST requests to booking endpoints.

Practical database check (safe non-destructive approach):

SELECT id, field_value FROM wp_booking_table WHERE field_value LIKE '%<%';

If you find matches, inspect them carefully; remove or sanitize suspicious entries.

Note: Do not run any untrusted scripts in your admin browser session while investigating.

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Immediate mitigations (while you patch)

1. Update plugin to 10.14.2 (or later)
   • This is the single most important remediation. Apply updates on staging first if you must, but prioritize production patching when possible.
2. Limit user privileges temporarily
   • Disable or restrict new account registration.
   • Change contributor-level workflows: stop offering ‘Contributor’ role for new users until patched.
   • Remove or reduce privileges from accounts that do not need them.
3. Block the offending endpoints via WAF
   • Deploy rules that block POST/PUT requests containing suspicious payload patterns (script tags, onerror/onload attributes, javascript:).
   • Monitor admin page GET requests that include suspicious query strings.
4. Audit and sanitize stored data
   • Export booking entries and search for stored HTML or JavaScript. Remove or sanitize suspicious fields.
   • If you find evidence of a compromise, rotate admin passwords and review user accounts.
5. Harden admin access:
   • Enforce strong passwords on admin accounts.
   • Turn on two-factor authentication for administrators.
   • Limit admin access by IP if possible (allowlist IPs for wp-admin).
6. Apply Content Security Policy (CSP)
   • Implement a restrictive CSP that disallows inline scripts and restricts external script loading. Example header:
     Content-Security-Policy: default-src 'self'; script-src 'self'; object-src 'none'; frame-ancestors 'none';
   • CSP reduces the impact of XSS by preventing execution of injected inline scripts in many cases.
7. Temporary output escaping via snippet
   • If you cannot update plugin immediately, add defensive output escaping on pages that render booking content. For example, sanitize rendering by escaping HTML:

   // Example: Force plain text when rendering booking fields
   echo esc_html( $booking_field_value );
       

   • Or allow only safe HTML with wp_kses:

   $allowed = array(
     'a' => array('href' => true, 'title' => true, 'target' => true),
     'strong' => array(),
     'em' => array(),
     'br' => array(),
   );
   echo wp_kses( $booking_field_value, $allowed );
       

   • Note: Use these only when you know the template or output context; avoid modifying the plugin core unless you maintain changes and can revert once patched.
8. Monitor logs
   • Watch webserver logs, WAF logs, and wp-admin access logs for repeated attempts to post payloads or for admin users opening the same booking records.

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Long-term hardening (best practices)

• Treat all user-supplied content as untrusted. Apply validation, sanitization and escaping with the principle: sanitize input + escape on output.
• Use capability checks rigorously in plugin development: do not rely on role names; check specific capabilities.
• Keep a tight inventory of plugins and their update status; prioritize plugins that interact with user-supplied data.
• Regular code reviews for plugins that render HTML: ensure escaping functions (esc_html, esc_attr, esc_url, wp_kses) are used correctly for their context.
• Implement least privilege for users and consider a workflow that limits who can publish or submit content.
• Use a managed WAF that can apply virtual patches and block common payloads before they reach WordPress.

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How WP-Firewall protects you in this situation

At WP-Firewall we offer multiple layers of protection that help sites survive and recover from plugin vulnerabilities like stored XSS:

• Managed WAF rules: We deploy targeted WAF rules to detect and block XSS payloads targeting booking endpoints and admin pages. These rules match common patterns and obfuscation techniques used by attackers.
• Virtual patching (Pro plan): When a vulnerability is disclosed and before all sites can update, our virtual patch layer shields your site by neutralizing attack vectors at the web application layer without updating the vulnerable plugin immediately.
• Malware scanning and mitigation: Our scanners look for injected scripts, suspicious files and modifications that may indicate a successful XSS-driven post-exploitation.
• Mitigation of OWASP Top 10 risks: The free managed firewall includes protections tuned to mitigate the most common application-level threats, including XSS.
• Audit logs and alerting: We provide logging and alerts for anomalous POST/GET requests and suspicious admin behavior so you can act fast.
• Best-practice guidance: We provide checks and remediation steps (like those in this article) to help you repair any damage and prevent future incidents.

Note: Virtual patching and advanced remediation capabilities are included in higher tiers, while the free plan includes managed WAF and malware scanning that reduce exposure for many common attacks.

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Step-by-step remediation checklist

1. Confirm plugin version:
   • Login to WordPress admin → Plugins and verify Booking Calendar version. If <= 10.14.1, proceed.
2. Update Booking Calendar:
   • Backup site (files + database).
   • Update plugin to 10.14.2 or later.
   • Verify booking functionality on staging/production.
3. Audit booking data:
   • Search booking tables for HTML tags or scripted content and sanitize or remove suspicious values.
4. Reset and secure accounts:
   • Force password resets for admin users who viewed bookings recently (if you detect suspicious activity).
   • Review recently created users — disable or delete unknown accounts.
5. Deploy WAF rules:
   • Block HTTP requests to booking endpoints that contain <script, onerror=, onload=, javascript: or other suspicious constructs.
   • Monitor WAF alerts and whitelist legitimate integrations if necessary.
6. Turn on admin hardening:
   • Enable two-factor authentication for administrators.
   • Limit admin IP addresses, where feasible.
   • Make site registration restrictive or invite-only.
7. Review logs for indicators:
   • Check server logs, WAF logs, and WordPress activity logs for evidence of exploitation or lateral movement.
8. Notify stakeholders:
   • If you manage client sites, inform them of the update and steps taken.
   • If you detect a compromise, consider professional incident response.

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Indicators of Compromise (IOCs) & queries to run

Search your database and logs for the following patterns:

• DB fields containing:
  • “<script”
  • “onerror=”
  • “onload=”
  • “javascript:”
  • “document.cookie”
• Webserver/WAF logs:
  • POST requests to booking endpoints containing the above strings.
• Recent admin sessions that coincide with viewing the same booking ID that contains suspicious content.

Sample safe SQL (read-only) to find entries with potential HTML:

SELECT id, booking_field, created_at
FROM wp_booking_table
WHERE booking_field LIKE '%<script%' OR
      booking_field LIKE '%onerror=%' OR
      booking_field LIKE '%javascript:%';

Use proper precautions: read-only queries, backups and a staged analysis process.

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Developer guidance: safe output patterns

When developing or auditing WordPress code, use the correct escaping for the output context.

• HTML body/text content:
  • Utiliser esc_html() when outputting into HTML text nodes.
  • Exemple: echo esc_html( $value );
• HTML attributes:
  • Utiliser esc_attr() when outputting into HTML attributes.
  • Exemple: printf( '<div data-note="%s">', esc_attr( $note ) );
• URLs:
  • Utiliser esc_url_raw() before storing, esc_url() before outputting.
• Allow limited HTML:
  • Utiliser wp_kses() to define an allowlist of tags and attributes if you legitimately need HTML (e.g., <a>, <strong>).
  • Exemple:

  $allowed = array(
    'a' => array( 'href' => true, 'rel' => true, 'target' => true ),
    'strong' => array(),
    'em' => array(),
    'br' => array()
  );
  $safe = wp_kses( $user_input, $allowed );
  echo $safe;
      

Remember: sanitize input, but always escape on output — input validation alone is insufficient because contexts vary.

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If you find evidence of compromise: emergency steps

1. Take the site offline or temporarily disable public access to admin areas until you contain the incident.
2. Revoke active sessions for all admin users and rotate credentials.
3. Remove any suspicious plugins or files found via scans.
4. Restore from a known clean backup if available.
5. Conduct a forensic review of when and how the compromise occurred — check web server timestamps, logs, and any newly created admin accounts or modifications.
6. If you cannot contain by yourself, engage a professional incident response service.

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Frequently asked questions

Q: If I’m a small blog with only one admin, is this still important?
A: Yes. Even a single admin account is a high-value target. Stored XSS may allow attackers to execute actions as that admin and fully compromise the site.

Q: Can a contributor exploit this without admin viewing the booking?
A: Stored XSS requires a victim to load the stored content. If admin users never view the particular booking record, the script won’t execute. However, attackers often try to trigger views (for example, by adding a comment to a recent booking or coordinating timing when admins review entries).

Q: Does a Content Security Policy guarantee protection?
A: CSP greatly reduces risk of many XSS attacks but is not a silver bullet. CSP should be part of a layered defense with proper escaping and input validation.

Q: Can I rely only on a firewall?
A: A WAF significantly reduces exposure and can mitigate exploitation, but it should complement — not replace — timely patching and secure coding practices.

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Secure Your Booking Forms with WP-Firewall Free Plan

If you want immediate baseline protection while you apply updates and perform audits, consider starting with WP-Firewall’s Basic (Free) plan. It includes managed firewall protections, an application layer WAF that blocks common XSS payloads, unlimited bandwidth for protections, a malware scanner to detect injected scripts, and targeted mitigation for OWASP Top 10 risks. These protections reduce the attack surface and give you breathing room to update plugins and sanitize stored data.

Start your free protection here: https://my.wp-firewall.com/buy/wp-firewall-free-plan/

(Upgrade options are available if you need automated malware removal, IP blacklisting/whitelisting, monthly security reporting, or virtual patching for rapid protection.)

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Closing notes from WP-Firewall security team

Plugin vulnerabilities like this one are a reminder that WordPress sites are composed systems: a minor gap in any plugin can escalate into a site-wide compromise if not handled carefully. The combination of user-supplied inputs, persistent storage and admin-facing rendering makes stored XSS particularly dangerous.

Our recommended priority:

1. Update Booking Calendar to 10.14.2 or later as soon as possible.
2. Audit stored booking data and sanitize suspicious entries.
3. Harden admin access and restrict registrations if not required.
4. Deploy WAF protections (our free plan includes managed firewall & WAF).
5. Consider CSP, 2FA and stronger role management for long-term resilience.

If you need help assessing risk across multiple sites, deploying virtual patching, or running a remediation engagement, our security team at WP-Firewall can assist — from automated protections to incident response planning.

Stay safe, and act quickly: updating plugins and applying basic hardening reduces the window attackers have to weaponize disclosed vulnerabilities.