Clean connection headers for forward auth request only

Co-authored-by: Kevin Pollet <pollet.kevin@gmail.com>

docs/content/migration/v2.md

@@ -637,3 +637,15 @@ Increasing the `readTimeout` value could be the solution notably if you are deal
 - TCP: `Error while handling TCP connection: readfrom tcp X.X.X.X:X->X.X.X.X:X: read tcp X.X.X.X:X->X.X.X.X:X: i/o timeout`
 - HTTP: `'499 Client Closed Request' caused by: context canceled`
 - HTTP: `ReverseProxy read error during body copy: read tcp X.X.X.X:X->X.X.X.X:X: use of closed network connection`
+
+## v2.11.3
+
+### Connection headers
+
+In `v2.11.3`, the handling of the request Connection headers directives has changed to prevent any abuse.
+Before, Traefik removed any header listed in the Connection header just before forwarding the request to the backends.
+Now, Traefik removes the headers listed in the Connection header as soon as the request is handled.
+As a consequence, middlewares do not have access to those Connection headers,
+and a new option has been introduced to specify which ones could go through the middleware chain before being removed: `<entrypoint>.forwardedHeaders.connection`.
+
+Please check out the [entrypoint forwarded headers connection option configuration](../routing/entrypoints.md#forwarded-headers) documentation.

pkg/middlewares/auth/connectionheader.go

@@ -13,16 +13,21 @@ const (
 	upgradeHeader    = "Upgrade"
 )
 
-// Remover removes hop-by-hop headers listed in the "Connection" header.
+// RemoveConnectionHeaders removes hop-by-hop headers listed in the "Connection" header.
 // See RFC 7230, section 6.1.
-func Remover(next http.Handler) http.HandlerFunc {
-	return func(rw http.ResponseWriter, req *http.Request) {
+func RemoveConnectionHeaders(req *http.Request) {
 	var reqUpType string
 	if httpguts.HeaderValuesContainsToken(req.Header[connectionHeader], upgradeHeader) {
 		reqUpType = req.Header.Get(upgradeHeader)
 	}
 
-		removeConnectionHeaders(req.Header)
+	for _, f := range req.Header[connectionHeader] {
+		for _, sf := range strings.Split(f, ",") {
+			if sf = textproto.TrimString(sf); sf != "" {
+				req.Header.Del(sf)
+			}
+		}
+	}
 
 	if reqUpType != "" {
 		req.Header.Set(connectionHeader, upgradeHeader)
@@ -30,17 +35,4 @@ func Remover(next http.Handler) http.HandlerFunc {
 	} else {
 		req.Header.Del(connectionHeader)
 	}
-
-		next.ServeHTTP(rw, req)
-	}
-}
-
-func removeConnectionHeaders(h http.Header) {
-	for _, f := range h[connectionHeader] {
-		for _, sf := range strings.Split(f, ",") {
-			if sf = textproto.TrimString(sf); sf != "" {
-				h.Del(sf)
-			}
-		}
-	}
 }

pkg/middlewares/auth/connectionheader_test.go

@@ -50,19 +50,13 @@ func TestRemover(t *testing.T) {
 		t.Run(test.desc, func(t *testing.T) {
 			t.Parallel()
 
-			next := http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {})
-
-			h := Remover(next)
-
 			req := httptest.NewRequest(http.MethodGet, "https://localhost", nil)
 
 			for k, v := range test.reqHeaders {
 				req.Header.Set(k, v)
 			}
 
-			rw := httptest.NewRecorder()
-
-			h.ServeHTTP(rw, req)
+			RemoveConnectionHeaders(req)
 
 			assert.Equal(t, test.expected, req.Header)
 		})

pkg/middlewares/auth/forward.go

@@ -89,7 +89,7 @@ func NewForward(ctx context.Context, next http.Handler, config dynamic.ForwardAu
 		fa.authResponseHeadersRegex = re
 	}
 
-	return Remover(fa), nil
+	return fa, nil
 }
 
 func (fa *forwardAuth) GetTracingInformation() (string, ext.SpanKindEnum) {
@@ -195,6 +195,8 @@ func (fa *forwardAuth) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 
 func writeHeader(req, forwardReq *http.Request, trustForwardHeader bool, allowedHeaders []string) {
 	utils.CopyHeaders(forwardReq.Header, req.Header)
+
+	RemoveConnectionHeaders(forwardReq)
 	utils.RemoveHeaders(forwardReq.Header, hopHeaders...)
 
 	forwardReq.Header = filterForwardRequestHeaders(forwardReq.Header, allowedHeaders)