GHSA-jmpx-686v-c3wx

# Unauthorized Reflected XSS in the constructor of the `Downloader` class

**Product**: Phpspreadsheet
**Version**: version 3.6.0
**CWE-ID**: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
**CVSS vector v.3.1**: 8.2 (AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:N)
**CVSS vector v.4.0**: 8.3 (AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:H/VA:N/SC:L/SI:H/SA:L)
**Description**: using the `/vendor/phpoffice/phpspreadsheet/samples/download.php` script, an attacker can perform a XSS-type attack
**Impact**: execution of arbitrary JavaScript code in the browser
**Vulnerable component**: the constructor of the `Downloader` class
**Exploitation conditions**: an unauthorized user
**Mitigation**: sanitization of the `name` and `type` variables
**Researcher**: Aleksey Solovev (Positive Technologies)

# Research

The researcher discovered zero-day vulnerability Unauthorized Reflected Cross-Site Scripting (XSS) (in the constructor of the `Downloader` class) in Phpspreadsheet.

The latest version (3.6.0) of the `phpoffice/phpspreadsheet` library was installed. The installation was carried out with the inclusion of examples.

*Listing 1. Installing the `phpoffice/phpspreadsheet` library*
```
$ composer require phpoffice/phpspreadsheet --prefer-source
```

The `./vendor/phpoffice/phpspreadsheet/samples/download.php` file processes the GET parameters `name` and `type`.


*Figure 1. The `./vendor/phpoffice/phpspreadsheet/samples/download.php` file accepts GET parameters.*

Consider the constructor of the `Downloader` class, where GET parameters are passed. Error is displayed without sanitization using GET parameters transmitted from the user.


*Figure 2. Error is displayed without sanitization*

When clicking on the following link, arbitrary JavaScript code will be executed.

*Listing 2.*
```
https://192.***.***.***/vendor/phpoffice/phpspreadsheet/samples/download.php?name=%3Cimg%20src=1%20onerror=alert()%3E&type=1
```

Demonstration of the execution of arbitrary JavaScript code.

<img width="537" alt="fig3" src="https://github.com/user-attachments/assets/745d6e21-396f-4357-8ff8-e856adf15fee" />

*Figure 3. Executing arbitrary JavaScript code*

# Credit
This vulnerability was discovered by **Aleksey Solovev (Positive Technologies)**