PhpSpreadsheet HTML writer is vulnerable to Cross-Site Scripting via style information

PHPSpreadsheet is a pure PHP library for reading and writing spreadsheet files. In affected versions \PhpOffice\PhpSpreadsheet\Writer\Html doesn't sanitize spreadsheet styling information such as font names, allowing an attacker to inject arbitrary JavaScript on the page. As a result an attacker may used a crafted spreadsheet to fully takeover a session of a user viewing spreadsheet files as HTML. This issue has been addressed in release version 2.1.0. All users are advised to upgrade. There are no known workarounds for this vulnerability.