GHSA-996f-334j-67g7 Easy!Appointments disable_booking_message rendered as raw HTML on public booking page — Stored XSS

• Packagist alextselegidis/easyappointments: <= 1.5.2 (no fix yet)

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: ```php ``` 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: ```javascript // 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: ```php // 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: ```php // 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: ```php // application/views/pages/booking_message.php line 10-12 ``` 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: ```http POST /index.php/booking_settings/save HTTP/1.1 Host: 127.0.0.1:18094 Cookie: Content-Type: application/x-www-form-urlencoded csrf_token=&booking_settings[0][name]=disable_booking&booking_settings[0][value]=1&booking_settings[1][name]=disable_booking_message&booking_settings[1][value]= ``` Response: `200 OK` — settings saved successfully Step 2 — Unauthenticated visitor opens public booking page: ```http GET / HTTP/1.1 Host: 127.0.0.1:18094 (no authentication) ``` Observed response fragment: ```html ``` 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: ```php // application/views/pages/booking_message.php ``` 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