Description
An input-validation flaw was discovered in the Go programming language built
in CGI implementation, which set the environment variable 'HTTP_PROXY' using the
incoming 'Proxy' HTTP-request header. The environment variable 'HTTP_PROXY' is
used by numerous web clients, including Go's net/http package, to specify a
proxy server to use for HTTP and, in some cases, HTTPS requests. This meant that
when a CGI-based web application ran, an attacker could specify a proxy server
which the application then used for subsequent outgoing requests, allowing a
man-in-the-middle attack. (CVE-2016-5386)