Go before 1.14.8 and 1.15.x before 1.15.1 allows XSS because text/html is the default for CGI/FCGI handlers that lack a Content-Type header.
https://www.oracle.com/security-alerts/cpuApr2021.html
https://www.oracle.com//security-alerts/cpujul2021.html
https://security.netapp.com/advisory/ntap-20200924-0003/
http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00002.html
http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00000.html