[client] Force TLS1.2 for RDP with Win11/Server2025 for CredSSP compatibility (#4617)

client/wasm/internal/rdp/cert_validation.go

@@ -73,8 +73,8 @@ func (p *RDCleanPathProxy) validateCertificateWithJS(conn *proxyConnection, cert
 	}
 }
 
-func (p *RDCleanPathProxy) getTLSConfigWithValidation(conn *proxyConnection) *tls.Config {
+func (p *RDCleanPathProxy) getTLSConfigWithValidation(conn *proxyConnection, requiresCredSSP bool) *tls.Config {
-	return &tls.Config{
+	config := &tls.Config{
 		InsecureSkipVerify: true, // We'll validate manually after handshake
 		VerifyConnection: func(cs tls.ConnectionState) error {
 			var certChain [][]byte
@@ -93,4 +93,15 @@ func (p *RDCleanPathProxy) getTLSConfigWithValidation(conn *proxyConnection) *tl
 			return nil
 		},
 	}
+
+	// CredSSP (NLA) requires TLS 1.2 - it's incompatible with TLS 1.3
+	if requiresCredSSP {
+		config.MinVersion = tls.VersionTLS12
+		config.MaxVersion = tls.VersionTLS12
+	} else {
+		config.MinVersion = tls.VersionTLS12
+		config.MaxVersion = tls.VersionTLS13
+	}
+
+	return config
 }

client/wasm/internal/rdp/rdcleanpath.go

@@ -6,11 +6,13 @@ import (
 	"context"
 	"crypto/tls"
 	"encoding/asn1"
+	"errors"
 	"fmt"
 	"io"
 	"net"
 	"sync"
 	"syscall/js"
+	"time"
 
 	log "github.com/sirupsen/logrus"
 )
@@ -19,18 +21,34 @@ const (
 	RDCleanPathVersion     = 3390
 	RDCleanPathProxyHost   = "rdcleanpath.proxy.local"
 	RDCleanPathProxyScheme = "ws"
+
+	rdpDialTimeout = 15 * time.Second
+
+	GeneralErrorCode = 1
+	WSAETimedOut     = 10060
+	WSAEConnRefused  = 10061
+	WSAEConnAborted  = 10053
+	WSAEConnReset    = 10054
+	WSAEGenericError = 10050
 )
 
 type RDCleanPathPDU struct {
-	Version           int64    `asn1:"tag:0,explicit"`
+	Version           int64          `asn1:"tag:0,explicit"`
-	Error             []byte   `asn1:"tag:1,explicit,optional"`
+	Error             RDCleanPathErr `asn1:"tag:1,explicit,optional"`
-	Destination       string   `asn1:"utf8,tag:2,explicit,optional"`
+	Destination       string         `asn1:"utf8,tag:2,explicit,optional"`
-	ProxyAuth         string   `asn1:"utf8,tag:3,explicit,optional"`
+	ProxyAuth         string         `asn1:"utf8,tag:3,explicit,optional"`
-	ServerAuth        string   `asn1:"utf8,tag:4,explicit,optional"`
+	ServerAuth        string         `asn1:"utf8,tag:4,explicit,optional"`
-	PreconnectionBlob string   `asn1:"utf8,tag:5,explicit,optional"`
+	PreconnectionBlob string         `asn1:"utf8,tag:5,explicit,optional"`
-	X224ConnectionPDU []byte   `asn1:"tag:6,explicit,optional"`
+	X224ConnectionPDU []byte         `asn1:"tag:6,explicit,optional"`
-	ServerCertChain   [][]byte `asn1:"tag:7,explicit,optional"`
+	ServerCertChain   [][]byte       `asn1:"tag:7,explicit,optional"`
-	ServerAddr        string   `asn1:"utf8,tag:9,explicit,optional"`
+	ServerAddr        string         `asn1:"utf8,tag:9,explicit,optional"`
+}
+
+type RDCleanPathErr struct {
+	ErrorCode      int16 `asn1:"tag:0,explicit"`
+	HTTPStatusCode int16 `asn1:"tag:1,explicit,optional"`
+	WSALastError   int16 `asn1:"tag:2,explicit,optional"`
+	TLSAlertCode   int8  `asn1:"tag:3,explicit,optional"`
 }
 
 type RDCleanPathProxy struct {
@@ -210,9 +228,13 @@ func (p *RDCleanPathProxy) handleDirectRDP(conn *proxyConnection, firstPacket []
 	destination := conn.destination
 	log.Infof("Direct RDP mode: Connecting to %s via NetBird", destination)
 
-	rdpConn, err := p.nbClient.Dial(conn.ctx, "tcp", destination)
+	ctx, cancel := context.WithTimeout(conn.ctx, rdpDialTimeout)
+	defer cancel()
+
+	rdpConn, err := p.nbClient.Dial(ctx, "tcp", destination)
 	if err != nil {
 		log.Errorf("Failed to connect to %s: %v", destination, err)
+		p.sendRDCleanPathError(conn, newWSAError(err))
 		return
 	}
 	conn.rdpConn = rdpConn
@@ -220,6 +242,7 @@ func (p *RDCleanPathProxy) handleDirectRDP(conn *proxyConnection, firstPacket []
 	_, err = rdpConn.Write(firstPacket)
 	if err != nil {
 		log.Errorf("Failed to write first packet: %v", err)
+		p.sendRDCleanPathError(conn, newWSAError(err))
 		return
 	}
 
@@ -227,6 +250,7 @@ func (p *RDCleanPathProxy) handleDirectRDP(conn *proxyConnection, firstPacket []
 	n, err := rdpConn.Read(response)
 	if err != nil {
 		log.Errorf("Failed to read X.224 response: %v", err)
+		p.sendRDCleanPathError(conn, newWSAError(err))
 		return
 	}
 
@@ -269,3 +293,52 @@ func (p *RDCleanPathProxy) sendToWebSocket(conn *proxyConnection, data []byte) {
 		conn.wsHandlers.Call("send", uint8Array.Get("buffer"))
 	}
 }
+
+func (p *RDCleanPathProxy) sendRDCleanPathError(conn *proxyConnection, pdu RDCleanPathPDU) {
+	data, err := asn1.Marshal(pdu)
+	if err != nil {
+		log.Errorf("Failed to marshal error PDU: %v", err)
+		return
+	}
+	p.sendToWebSocket(conn, data)
+}
+
+func errorToWSACode(err error) int16 {
+	if err == nil {
+		return WSAEGenericError
+	}
+	var netErr *net.OpError
+	if errors.As(err, &netErr) && netErr.Timeout() {
+		return WSAETimedOut
+	}
+	if errors.Is(err, context.DeadlineExceeded) {
+		return WSAETimedOut
+	}
+	if errors.Is(err, context.Canceled) {
+		return WSAEConnAborted
+	}
+	if errors.Is(err, io.EOF) {
+		return WSAEConnReset
+	}
+	return WSAEGenericError
+}
+
+func newWSAError(err error) RDCleanPathPDU {
+	return RDCleanPathPDU{
+		Version: RDCleanPathVersion,
+		Error: RDCleanPathErr{
+			ErrorCode:    GeneralErrorCode,
+			WSALastError: errorToWSACode(err),
+		},
+	}
+}
+
+func newHTTPError(statusCode int16) RDCleanPathPDU {
+	return RDCleanPathPDU{
+		Version: RDCleanPathVersion,
+		Error: RDCleanPathErr{
+			ErrorCode:      GeneralErrorCode,
+			HTTPStatusCode: statusCode,
+		},
+	}
+}

client/wasm/internal/rdp/rdcleanpath_handlers.go

@@ -3,6 +3,7 @@
 package rdp
 
 import (
+	"context"
 	"crypto/tls"
 	"encoding/asn1"
 	"io"
@@ -11,11 +12,17 @@ import (
 	log "github.com/sirupsen/logrus"
 )
 
+const (
+	// MS-RDPBCGR: confusingly named, actually means PROTOCOL_HYBRID (CredSSP)
+	protocolSSL      = 0x00000001
+	protocolHybridEx = 0x00000008
+)
+
 func (p *RDCleanPathProxy) processRDCleanPathPDU(conn *proxyConnection, pdu RDCleanPathPDU) {
 	log.Infof("Processing RDCleanPath PDU: Version=%d, Destination=%s", pdu.Version, pdu.Destination)
 
 	if pdu.Version != RDCleanPathVersion {
-		p.sendRDCleanPathError(conn, "Unsupported version")
+		p.sendRDCleanPathError(conn, newHTTPError(400))
 		return
 	}
 
@@ -24,10 +31,13 @@ func (p *RDCleanPathProxy) processRDCleanPathPDU(conn *proxyConnection, pdu RDCl
 		destination = pdu.Destination
 	}
 
-	rdpConn, err := p.nbClient.Dial(conn.ctx, "tcp", destination)
+	ctx, cancel := context.WithTimeout(conn.ctx, rdpDialTimeout)
+	defer cancel()
+
+	rdpConn, err := p.nbClient.Dial(ctx, "tcp", destination)
 	if err != nil {
 		log.Errorf("Failed to connect to %s: %v", destination, err)
-		p.sendRDCleanPathError(conn, "Connection failed")
+		p.sendRDCleanPathError(conn, newWSAError(err))
 		p.cleanupConnection(conn)
 		return
 	}
@@ -40,6 +50,34 @@ func (p *RDCleanPathProxy) processRDCleanPathPDU(conn *proxyConnection, pdu RDCl
 	p.setupTLSConnection(conn, pdu)
 }
 
+// detectCredSSPFromX224 checks if the X.224 response indicates NLA/CredSSP is required.
+// Per MS-RDPBCGR spec: byte 11 = TYPE_RDP_NEG_RSP (0x02), bytes 15-18 = selectedProtocol flags.
+// Returns (requiresTLS12, selectedProtocol, detectionSuccessful).
+func (p *RDCleanPathProxy) detectCredSSPFromX224(x224Response []byte) (bool, uint32, bool) {
+	const minResponseLength = 19
+
+	if len(x224Response) < minResponseLength {
+		return false, 0, false
+	}
+
+	// Per X.224 specification:
+	//   x224Response[0] == 0x03: Length of X.224 header (3 bytes)
+	//   x224Response[5] == 0xD0: X.224 Data TPDU code
+	if x224Response[0] != 0x03 || x224Response[5] != 0xD0 {
+		return false, 0, false
+	}
+
+	if x224Response[11] == 0x02 {
+		flags := uint32(x224Response[15]) | uint32(x224Response[16])<<8 |
+			uint32(x224Response[17])<<16 | uint32(x224Response[18])<<24
+
+		hasNLA := (flags & (protocolSSL | protocolHybridEx)) != 0
+		return hasNLA, flags, true
+	}
+
+	return false, 0, false
+}
+
 func (p *RDCleanPathProxy) setupTLSConnection(conn *proxyConnection, pdu RDCleanPathPDU) {
 	var x224Response []byte
 	if len(pdu.X224ConnectionPDU) > 0 {
@@ -47,7 +85,7 @@ func (p *RDCleanPathProxy) setupTLSConnection(conn *proxyConnection, pdu RDClean
 		_, err := conn.rdpConn.Write(pdu.X224ConnectionPDU)
 		if err != nil {
 			log.Errorf("Failed to write X.224 PDU: %v", err)
-			p.sendRDCleanPathError(conn, "Failed to forward X.224")
+			p.sendRDCleanPathError(conn, newWSAError(err))
 			return
 		}
 
@@ -55,21 +93,32 @@ func (p *RDCleanPathProxy) setupTLSConnection(conn *proxyConnection, pdu RDClean
 		n, err := conn.rdpConn.Read(response)
 		if err != nil {
 			log.Errorf("Failed to read X.224 response: %v", err)
-			p.sendRDCleanPathError(conn, "Failed to read X.224 response")
+			p.sendRDCleanPathError(conn, newWSAError(err))
 			return
 		}
 		x224Response = response[:n]
 		log.Debugf("Received X.224 Connection Confirm (%d bytes)", n)
 	}
 
-	tlsConfig := p.getTLSConfigWithValidation(conn)
+	requiresCredSSP, selectedProtocol, detected := p.detectCredSSPFromX224(x224Response)
+	if detected {
+		if requiresCredSSP {
+			log.Warnf("Detected NLA/CredSSP (selectedProtocol: 0x%08X), forcing TLS 1.2 for compatibility", selectedProtocol)
+		} else {
+			log.Warnf("No NLA/CredSSP detected (selectedProtocol: 0x%08X), allowing up to TLS 1.3", selectedProtocol)
+		}
+	} else {
+		log.Warnf("Could not detect RDP security protocol, allowing up to TLS 1.3")
+	}
+
+	tlsConfig := p.getTLSConfigWithValidation(conn, requiresCredSSP)
 
 	tlsConn := tls.Client(conn.rdpConn, tlsConfig)
 	conn.tlsConn = tlsConn
 
 	if err := tlsConn.Handshake(); err != nil {
 		log.Errorf("TLS handshake failed: %v", err)
-		p.sendRDCleanPathError(conn, "TLS handshake failed")
+		p.sendRDCleanPathError(conn, newWSAError(err))
 		return
 	}
 
@@ -106,47 +155,6 @@ func (p *RDCleanPathProxy) setupTLSConnection(conn *proxyConnection, pdu RDClean
 	p.cleanupConnection(conn)
 }
 
-func (p *RDCleanPathProxy) setupPlainConnection(conn *proxyConnection, pdu RDCleanPathPDU) {
-	if len(pdu.X224ConnectionPDU) > 0 {
-		log.Debugf("Forwarding X.224 Connection Request (%d bytes)", len(pdu.X224ConnectionPDU))
-		_, err := conn.rdpConn.Write(pdu.X224ConnectionPDU)
-		if err != nil {
-			log.Errorf("Failed to write X.224 PDU: %v", err)
-			p.sendRDCleanPathError(conn, "Failed to forward X.224")
-			return
-		}
-
-		response := make([]byte, 1024)
-		n, err := conn.rdpConn.Read(response)
-		if err != nil {
-			log.Errorf("Failed to read X.224 response: %v", err)
-			p.sendRDCleanPathError(conn, "Failed to read X.224 response")
-			return
-		}
-
-		responsePDU := RDCleanPathPDU{
-			Version:           RDCleanPathVersion,
-			X224ConnectionPDU: response[:n],
-			ServerAddr:        conn.destination,
-		}
-
-		p.sendRDCleanPathPDU(conn, responsePDU)
-	} else {
-		responsePDU := RDCleanPathPDU{
-			Version:    RDCleanPathVersion,
-			ServerAddr: conn.destination,
-		}
-		p.sendRDCleanPathPDU(conn, responsePDU)
-	}
-
-	go p.forwardConnToWS(conn, conn.rdpConn, "TCP")
-	go p.forwardWSToConn(conn, conn.rdpConn, "TCP")
-
-	<-conn.ctx.Done()
-	log.Debug("TCP connection context done, cleaning up")
-	p.cleanupConnection(conn)
-}
-
 func (p *RDCleanPathProxy) sendRDCleanPathPDU(conn *proxyConnection, pdu RDCleanPathPDU) {
 	data, err := asn1.Marshal(pdu)
 	if err != nil {
@@ -158,21 +166,6 @@ func (p *RDCleanPathProxy) sendRDCleanPathPDU(conn *proxyConnection, pdu RDClean
 	p.sendToWebSocket(conn, data)
 }
 
-func (p *RDCleanPathProxy) sendRDCleanPathError(conn *proxyConnection, errorMsg string) {
-	pdu := RDCleanPathPDU{
-		Version: RDCleanPathVersion,
-		Error:   []byte(errorMsg),
-	}
-
-	data, err := asn1.Marshal(pdu)
-	if err != nil {
-		log.Errorf("Failed to marshal error PDU: %v", err)
-		return
-	}
-
-	p.sendToWebSocket(conn, data)
-}
-
 func (p *RDCleanPathProxy) readWebSocketMessage(conn *proxyConnection) ([]byte, error) {
 	msgChan := make(chan []byte)
 	errChan := make(chan error)