The issue is related to a bypass of the Cross-site Scripting (XSS) sanitizer in phpoffice/phpspreadsheet, a pure PHP library for reading and writing spreadsheet files. This bypass is achieved using the javascript protocol and special characters. An attacker can use special characters to generate an HTML link that, when clicked, executes arbitrary JavaScript code in the browser. The vulnerable component is the `PhpOfficePhpSpreadsheetWriterHtml` class, specifically the `generateRow` method. The exploitation conditions involve a user viewing a specially generated XML file.