Print access logs for rejected requests and warn about new behavior

pkg/server/router/deny.go

@@ -0,0 +1,62 @@
+package router
+
+import (
+	"net/http"
+	"strings"
+
+	"github.com/rs/zerolog/log"
+)
+
+// denyFragment rejects the request if the URL path contains a fragment (hash character).
+// When go receives an HTTP request, it assumes the absence of fragment URL.
+// However, it is still possible to send a fragment in the request.
+// In this case, Traefik will encode the '#' character, altering the request's intended meaning.
+// To avoid this behavior, the following function rejects requests that include a fragment in the URL.
+func denyFragment(h http.Handler) http.Handler {
+	return http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		if strings.Contains(req.URL.RawPath, "#") {
+			log.Debug().Msgf("Rejecting request because it contains a fragment in the URL path: %s", req.URL.RawPath)
+			rw.WriteHeader(http.StatusBadRequest)
+
+			return
+		}
+
+		h.ServeHTTP(rw, req)
+	})
+}
+
+// denyEncodedPathCharacters reject the request if the escaped path contains encoded characters in the given list.
+func denyEncodedPathCharacters(encodedCharacters map[string]struct{}, h http.Handler) http.Handler {
+	return http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		if len(encodedCharacters) == 0 {
+			h.ServeHTTP(rw, req)
+			return
+		}
+
+		escapedPath := req.URL.EscapedPath()
+
+		for i := 0; i < len(escapedPath); i++ {
+			if escapedPath[i] != '%' {
+				continue
+			}
+
+			// This should never happen as the standard library will reject requests containing invalid percent-encodings.
+			// This discards URLs with a percent character at the end.
+			if i+2 >= len(escapedPath) {
+				rw.WriteHeader(http.StatusBadRequest)
+				return
+			}
+
+			// This rejects a request with a path containing the given encoded characters.
+			if _, exists := encodedCharacters[escapedPath[i:i+3]]; exists {
+				log.Debug().Msgf("Rejecting request because it contains encoded character %s in the URL path: %s", escapedPath[i:i+3], escapedPath)
+				rw.WriteHeader(http.StatusBadRequest)
+				return
+			}
+
+			i += 2
+		}
+
+		h.ServeHTTP(rw, req)
+	})
+}