A flaw was found in the Go standard library packages before upstream versions 1.15 and 1.14.8. Both the net/http/cgi and net/http/fcgi packages use a default Content-Type response header value of "text/html", rather than "text/plain". This flaw allows an attacker to exploit this issue in applications using these packages by uploading crafted files, allowing a Cross-site Scripting attack (XSS). The highest threat from this vulnerability is to confidentiality and integrity.