FastCGI: ensure HTTP_HOST is set to the requested target host.

Previously, the HTTP_HOST environment variable was constructed from the
Host request header field, which doesn't work well with HTTP/2 and
HTTP/3 where Host may be supplanted by the ":authority" pseudo-header
field per RFC 9110, section 7.2. Also, it might give an incorrect
HTTP_HOST value from HTTP/1.x requests given in the absolute form, in
which case the Host header must be ignored by the server, per RFC 9112,
section 3.2.2.

The fix is to redefine the HTTP_HOST default from a protocol-specific
value given in the $host variable. This will now use the Host request
header field, ":authority" pseudo-header field, or request line target
URI depending on request HTTP version.

Also the CGI specification (RFC 3875, 4.1.18) notes

  The server SHOULD set meta-variables specific to the protocol and
  scheme for the request. Interpretation of protocol-specific
  variables depends on the protocol version in SERVER_PROTOCOL.

Closes: https://github.com/nginx/nginx/issues/256
Closes: https://github.com/nginx/nginx/issues/455
Closes: https://github.com/nginx/nginx/issues/912
This commit is contained in:
Andrew Clayton 2025-12-13 07:05:27 +00:00
parent 6a67f71a4a
commit 71b18973b2

View file

@ -656,9 +656,18 @@ static ngx_str_t ngx_http_fastcgi_hide_headers[] = {
};
static ngx_keyval_t ngx_http_fastcgi_headers[] = {
{ ngx_string("HTTP_HOST"),
ngx_string("$host$is_request_port$request_port") },
{ ngx_null_string, ngx_null_string }
};
#if (NGX_HTTP_CACHE)
static ngx_keyval_t ngx_http_fastcgi_cache_headers[] = {
{ ngx_string("HTTP_HOST"),
ngx_string("$host$is_request_port$request_port") },
{ ngx_string("HTTP_IF_MODIFIED_SINCE"),
ngx_string("$upstream_cache_last_modified") },
{ ngx_string("HTTP_IF_UNMODIFIED_SINCE"), ngx_string("") },
@ -3276,7 +3285,8 @@ ngx_http_fastcgi_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
conf->params_source = prev->params_source;
}
rc = ngx_http_fastcgi_init_params(cf, conf, &conf->params, NULL);
rc = ngx_http_fastcgi_init_params(cf, conf, &conf->params,
ngx_http_fastcgi_headers);
if (rc != NGX_OK) {
return NGX_CONF_ERROR;
}