Improper input validation in net/http and net/http/cgi

An input validation flaw in the CGI components allows the HTTP_PROXY environment variable to be set by the incoming Proxy header, which changes where Go by default proxies all outbound HTTP requests.

This environment variable is also used to set the outgoing proxy, enabling an attacker to insert a proxy into outgoing requests of a CGI program.

Read more about “httpoxy” here: https://httpoxy.org.