rpc: dns rebind protection (#15962)

* cmd,node,rpc: add allowedHosts to prevent dns rebinding attacks

* p2p,node: Fix bug with dumpconfig introduced in r54aeb8e4c0bb9f0e7a6c67258af67df3b266af3d

* rpc: add wildcard support for rpcallowedhosts + go fmt

* cmd/geth, cmd/utils, node, rpc: ignore direct ip(v4/6) addresses in rpc virtual hostnames check

* http, rpc, utils: make vhosts into map, address review concerns

* node: change log messages to use geth standard (not sprintf)

* rpc: fix spelling

Author: holiman

cmd/geth/main.go

@@ -114,6 +114,7 @@ var (
 		utils.VMEnableDebugFlag,
 		utils.NetworkIdFlag,
 		utils.RPCCORSDomainFlag,
+		utils.RPCVirtualHostsFlag,
 		utils.EthStatsURLFlag,
 		utils.MetricsEnabledFlag,
 		utils.FakePoWFlag,

cmd/geth/usage.go

@@ -156,6 +156,7 @@ var AppHelpFlagGroups = []flagGroup{
 			utils.IPCDisabledFlag,
 			utils.IPCPathFlag,
 			utils.RPCCORSDomainFlag,
+			utils.RPCVirtualHostsFlag,
 			utils.JSpathFlag,
 			utils.ExecFlag,
 			utils.PreloadJSFlag,

cmd/utils/flags.go

@@ -397,6 +397,11 @@ var (
 		Usage: "Comma separated list of domains from which to accept cross origin requests (browser enforced)",
 		Value: "",
 	}
+	RPCVirtualHostsFlag = cli.StringFlag{
+		Name:  "rpcvhosts",
+		Usage: "Comma separated list of virtual hostnames from which to accept requests (server enforced). Accepts '*' wildcard.",
+		Value: "localhost",
+	}
 	RPCApiFlag = cli.StringFlag{
 		Name:  "rpcapi",
 		Usage: "API's offered over the HTTP-RPC interface",
@@ -690,6 +695,8 @@ func setHTTP(ctx *cli.Context, cfg *node.Config) {
 	if ctx.GlobalIsSet(RPCApiFlag.Name) {
 		cfg.HTTPModules = splitAndTrim(ctx.GlobalString(RPCApiFlag.Name))
 	}
+
+	cfg.HTTPVirtualHosts = splitAndTrim(ctx.GlobalString(RPCVirtualHostsFlag.Name))
 }
 
 // setWS creates the WebSocket RPC listener interface string from the set

node/api.go

@@ -114,7 +114,7 @@ func (api *PrivateAdminAPI) PeerEvents(ctx context.Context) (*rpc.Subscription,
 }
 
 // StartRPC starts the HTTP RPC API server.
-func (api *PrivateAdminAPI) StartRPC(host *string, port *int, cors *string, apis *string) (bool, error) {
+func (api *PrivateAdminAPI) StartRPC(host *string, port *int, cors *string, apis *string, vhosts *string) (bool, error) {
 	api.node.lock.Lock()
 	defer api.node.lock.Unlock()
 
@@ -141,6 +141,14 @@ func (api *PrivateAdminAPI) StartRPC(host *string, port *int, cors *string, apis
 		}
 	}
 
+	allowedVHosts := api.node.config.HTTPVirtualHosts
+	if vhosts != nil {
+		allowedVHosts = nil
+		for _, vhost := range strings.Split(*host, ",") {
+			allowedVHosts = append(allowedVHosts, strings.TrimSpace(vhost))
+		}
+	}
+
 	modules := api.node.httpWhitelist
 	if apis != nil {
 		modules = nil
@@ -149,7 +157,7 @@ func (api *PrivateAdminAPI) StartRPC(host *string, port *int, cors *string, apis
 		}
 	}
 
-	if err := api.node.startHTTP(fmt.Sprintf("%s:%d", *host, *port), api.node.rpcAPIs, modules, allowedOrigins); err != nil {
+	if err := api.node.startHTTP(fmt.Sprintf("%s:%d", *host, *port), api.node.rpcAPIs, modules, allowedOrigins, allowedVHosts); err != nil {
 		return false, err
 	}
 	return true, nil

node/config.go

@@ -105,6 +105,15 @@ type Config struct {
 	// useless for custom HTTP clients.
 	HTTPCors []string `toml:",omitempty"`
 
+	// HTTPVirtualHosts is the list of virtual hostnames which are allowed on incoming requests.
+	// This is by default {'localhost'}. Using this prevents attacks like
+	// DNS rebinding, which bypasses SOP by simply masquerading as being within the same
+	// origin. These attacks do not utilize CORS, since they are not cross-domain.
+	// By explicitly checking the Host-header, the server will not allow requests
+	// made against the server with a malicious host domain.
+	// Requests using ip address directly are not affected
+	HTTPVirtualHosts []string `toml:",omitempty"`
+
 	// HTTPModules is a list of API modules to expose via the HTTP RPC interface.
 	// If the module list is empty, all RPC API endpoints designated public will be
 	// exposed.
@@ -137,7 +146,7 @@ type Config struct {
 	WSExposeAll bool `toml:",omitempty"`
 
 	// Logger is a custom logger to use with the p2p.Server.
-	Logger log.Logger
+	Logger log.Logger `toml:",omitempty"`
 }
 
 // IPCEndpoint resolves an IPC endpoint based on a configured value, taking into

node/node.go

@@ -263,7 +263,7 @@ func (n *Node) startRPC(services map[reflect.Type]Service) error {
 		n.stopInProc()
 		return err
 	}
-	if err := n.startHTTP(n.httpEndpoint, apis, n.config.HTTPModules, n.config.HTTPCors); err != nil {
+	if err := n.startHTTP(n.httpEndpoint, apis, n.config.HTTPModules, n.config.HTTPCors, n.config.HTTPVirtualHosts); err != nil {
 		n.stopIPC()
 		n.stopInProc()
 		return err
@@ -287,7 +287,7 @@ func (n *Node) startInProc(apis []rpc.API) error {
 		if err := handler.RegisterName(api.Namespace, api.Service); err != nil {
 			return err
 		}
-		n.log.Debug(fmt.Sprintf("InProc registered %T under '%s'", api.Service, api.Namespace))
+		n.log.Debug("InProc registered", "service", api.Service, "namespace", api.Namespace)
 	}
 	n.inprocHandler = handler
 	return nil
@@ -313,7 +313,7 @@ func (n *Node) startIPC(apis []rpc.API) error {
 		if err := handler.RegisterName(api.Namespace, api.Service); err != nil {
 			return err
 		}
-		n.log.Debug(fmt.Sprintf("IPC registered %T under '%s'", api.Service, api.Namespace))
+		n.log.Debug("IPC registered", "service", api.Service, "namespace", api.Namespace)
 	}
 	// All APIs registered, start the IPC listener
 	var (
@@ -324,7 +324,7 @@ func (n *Node) startIPC(apis []rpc.API) error {
 		return err
 	}
 	go func() {
-		n.log.Info(fmt.Sprintf("IPC endpoint opened: %s", n.ipcEndpoint))
+		n.log.Info("IPC endpoint opened", "url", fmt.Sprintf("%s", n.ipcEndpoint))
 
 		for {
 			conn, err := listener.Accept()
@@ -337,7 +337,7 @@ func (n *Node) startIPC(apis []rpc.API) error {
 					return
 				}
 				// Not closed, just some error; report and continue
-				n.log.Error(fmt.Sprintf("IPC accept failed: %v", err))
+				n.log.Error("IPC accept failed", "err", err)
 				continue
 			}
 			go handler.ServeCodec(rpc.NewJSONCodec(conn), rpc.OptionMethodInvocation|rpc.OptionSubscriptions)
@@ -356,7 +356,7 @@ func (n *Node) stopIPC() {
 		n.ipcListener.Close()
 		n.ipcListener = nil
 
-		n.log.Info(fmt.Sprintf("IPC endpoint closed: %s", n.ipcEndpoint))
+		n.log.Info("IPC endpoint closed", "endpoint", n.ipcEndpoint)
 	}
 	if n.ipcHandler != nil {
 		n.ipcHandler.Stop()
@@ -365,7 +365,7 @@ func (n *Node) stopIPC() {
 }
 
 // startHTTP initializes and starts the HTTP RPC endpoint.
-func (n *Node) startHTTP(endpoint string, apis []rpc.API, modules []string, cors []string) error {
+func (n *Node) startHTTP(endpoint string, apis []rpc.API, modules []string, cors []string, vhosts []string) error {
 	// Short circuit if the HTTP endpoint isn't being exposed
 	if endpoint == "" {
 		return nil
@@ -382,7 +382,7 @@ func (n *Node) startHTTP(endpoint string, apis []rpc.API, modules []string, cors
 			if err := handler.RegisterName(api.Namespace, api.Service); err != nil {
 				return err
 			}
-			n.log.Debug(fmt.Sprintf("HTTP registered %T under '%s'", api.Service, api.Namespace))
+			n.log.Debug("HTTP registered", "service", api.Service, "namespace", api.Namespace)
 		}
 	}
 	// All APIs registered, start the HTTP listener
@@ -393,9 +393,8 @@ func (n *Node) startHTTP(endpoint string, apis []rpc.API, modules []string, cors
 	if listener, err = net.Listen("tcp", endpoint); err != nil {
 		return err
 	}
-	go rpc.NewHTTPServer(cors, handler).Serve(listener)
-	n.log.Info(fmt.Sprintf("HTTP endpoint opened: http://%s", endpoint))
-
+	go rpc.NewHTTPServer(cors, vhosts, handler).Serve(listener)
+	n.log.Info("HTTP endpoint opened", "url", fmt.Sprintf("http://%s", endpoint), "cors", strings.Join(cors, ","), "hvosts", strings.Join(vhosts, ","))
 	// All listeners booted successfully
 	n.httpEndpoint = endpoint
 	n.httpListener = listener
@@ -410,7 +409,7 @@ func (n *Node) stopHTTP() {
 		n.httpListener.Close()
 		n.httpListener = nil
 
-		n.log.Info(fmt.Sprintf("HTTP endpoint closed: http://%s", n.httpEndpoint))
+		n.log.Info("HTTP endpoint closed", "url", fmt.Sprintf("http://%s", n.httpEndpoint))
 	}
 	if n.httpHandler != nil {
 		n.httpHandler.Stop()
@@ -436,7 +435,7 @@ func (n *Node) startWS(endpoint string, apis []rpc.API, modules []string, wsOrig
 			if err := handler.RegisterName(api.Namespace, api.Service); err != nil {
 				return err
 			}
-			n.log.Debug(fmt.Sprintf("WebSocket registered %T under '%s'", api.Service, api.Namespace))
+			n.log.Debug("WebSocket registered", "service", api.Service, "namespace", api.Namespace)
 		}
 	}
 	// All APIs registered, start the HTTP listener
@@ -448,7 +447,7 @@ func (n *Node) startWS(endpoint string, apis []rpc.API, modules []string, wsOrig
 		return err
 	}
 	go rpc.NewWSServer(wsOrigins, handler).Serve(listener)
-	n.log.Info(fmt.Sprintf("WebSocket endpoint opened: ws://%s", listener.Addr()))
+	n.log.Info("WebSocket endpoint opened", "url", fmt.Sprintf("ws://%s", listener.Addr()))
 
 	// All listeners booted successfully
 	n.wsEndpoint = endpoint
@@ -464,7 +463,7 @@ func (n *Node) stopWS() {
 		n.wsListener.Close()
 		n.wsListener = nil
 
-		n.log.Info(fmt.Sprintf("WebSocket endpoint closed: ws://%s", n.wsEndpoint))
+		n.log.Info("WebSocket endpoint closed", "url", fmt.Sprintf("ws://%s", n.wsEndpoint))
 	}
 	if n.wsHandler != nil {
 		n.wsHandler.Stop()

p2p/server.go

@@ -142,7 +142,7 @@ type Config struct {
 	EnableMsgEvents bool
 
 	// Logger is a custom logger to use with the p2p.Server.
-	Logger log.Logger
+	Logger log.Logger `toml:",omitempty"`
 }
 
 // Server manages all peer connections.

rpc/http.go

@@ -31,6 +31,7 @@ import (
 	"time"
 
 	"github.com/rs/cors"
+	"strings"
 )
 
 const (
@@ -148,8 +149,11 @@ func (t *httpReadWriteNopCloser) Close() error {
 // NewHTTPServer creates a new HTTP RPC server around an API provider.
 //
 // Deprecated: Server implements http.Handler
-func NewHTTPServer(cors []string, srv *Server) *http.Server {
-	return &http.Server{Handler: newCorsHandler(srv, cors)}
+func NewHTTPServer(cors []string, vhosts []string, srv *Server) *http.Server {
+	// Wrap the CORS-handler within a host-handler
+	handler := newCorsHandler(srv, cors)
+	handler = newVHostHandler(vhosts, handler)
+	return &http.Server{Handler: handler}
 }
 
 // ServeHTTP serves JSON-RPC requests over HTTP.
@@ -195,7 +199,6 @@ func newCorsHandler(srv *Server, allowedOrigins []string) http.Handler {
 	if len(allowedOrigins) == 0 {
 		return srv
 	}
-
 	c := cors.New(cors.Options{
 		AllowedOrigins: allowedOrigins,
 		AllowedMethods: []string{http.MethodPost, http.MethodGet},
@@ -204,3 +207,51 @@ func newCorsHandler(srv *Server, allowedOrigins []string) http.Handler {
 	})
 	return c.Handler(srv)
 }
+
+// virtualHostHandler is a handler which validates the Host-header of incoming requests.
+// The virtualHostHandler can prevent DNS rebinding attacks, which do not utilize CORS-headers,
+// since they do in-domain requests against the RPC api. Instead, we can see on the Host-header
+// which domain was used, and validate that against a whitelist.
+type virtualHostHandler struct {
+	vhosts map[string]struct{}
+	next   http.Handler
+}
+
+// ServeHTTP serves JSON-RPC requests over HTTP, implements http.Handler
+func (h *virtualHostHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// if r.Host is not set, we can continue serving since a browser would set the Host header
+	if r.Host == "" {
+		h.next.ServeHTTP(w, r)
+		return
+	}
+	host, _, err := net.SplitHostPort(r.Host)
+	if err != nil {
+		// Either invalid (too many colons) or no port specified
+		host = r.Host
+	}
+	if ipAddr := net.ParseIP(host); ipAddr != nil {
+		// It's an IP address, we can serve that
+		h.next.ServeHTTP(w, r)
+		return
+
+	}
+	// Not an ip address, but a hostname. Need to validate
+	if _, exist := h.vhosts["*"]; exist {
+		h.next.ServeHTTP(w, r)
+		return
+	}
+	if _, exist := h.vhosts[host]; exist {
+		h.next.ServeHTTP(w, r)
+		return
+	}
+	http.Error(w, "invalid host specified", http.StatusForbidden)
+	return
+}
+
+func newVHostHandler(vhosts []string, next http.Handler) http.Handler {
+	vhostMap := make(map[string]struct{})
+	for _, allowedHost := range vhosts {
+		vhostMap[strings.ToLower(allowedHost)] = struct{}{}
+	}
+	return &virtualHostHandler{vhostMap, next}
+}