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 of the hyperlink base in the HTML page header. The HTML page is formed without sanitizing the hyperlink base. Versions 3.7.0, 2.3.5, 2.1.6, and 1.29.7 contain a patch for the issue.