PhpSpreadsheet has Cross-Site Scripting (XSS) vulnerability in custom properties

PhpSpreadsheet is a PHP library for reading and writing spreadsheet files. Versions prior to 3.7.0, 2.3.5, 2.1.6, and 1.29.7 have a cross-site scripting (XSS) vulnerability in custom properties. The HTML page is generated without clearing custom properties. Versions 3.7.0, 2.3.5, 2.1.6, and 1.29.7 contain a patch for the issue.