An issue was discovered in Joomla! before 3.9.3. A combination of specific web server configurations, in connection with specific file types and browser-side MIME-type sniffing, causes an XSS attack vector.Referenceshttps://developer.joomla.org/security-centre/766-20190202-core-browserside-mime-type-sniffing-causes-xss-attack-vectors
