Summary

Short summary of the problem. Make the impact and severity as clear as possible. For example: An unsafe deserialization vulnerability allows any unauthenticated user to execute arbitrary code on the server.

\PhpOffice\PhpSpreadsheet\Writer\Html doesn't sanitize spreadsheet styling information such as font names, allowing an attacker to inject arbitrary JavaScript on the page.

Details

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See GHSA-wgmf-q9vr-vww6

PoC

Complete instructions, including specific configuration details, to reproduce the vulnerability.

Example target script:

<?php

require 'vendor/autoload.php';

$reader = \PhpOffice\PhpSpreadsheet\IOFactory::createReader("Xlsx");
$spreadsheet = $reader->load(__DIR__ . '/book.xlsx');

$writer = new \PhpOffice\PhpSpreadsheet\Writer\Html($spreadsheet);
print($writer->generateHTMLAll());

Save this file in the same directory:

book.xlsx

Open index.php in a web browser. An alert should be displayed.

Impact

What kind of vulnerability is it? Who is impacted?

Full takeover of the session of users viewing spreadsheet files as HTML.