This report focuses on vulnerabilities on web-applications and web-sites from Cross-Site Scripting attacks (XSS). The different types of XSS attacks are examined: DOM-based, active and passive attacks. The spread of XSS attacks across platforms – government and financial institutions, transportation companies, hospitality and entertainment has been analyzed. Research and analysis of the security of corporate websites and their resistance to XSS attacks have been carried out. The basic guidelines for preventing valuable data theft and unauthorized access to websites and applications from XSS attacks are reviewed and systematized.