ssh: fix malformed exec payload panic (#5428)

.golangci.yml

@@ -61,6 +61,11 @@ linters:
     - legacy
     - std-error-handling
     rules:
+    # Keep h2c and HTTP/1.1 Upgrade:h2c compatibility until an explicit migration.
+    - linters:
+      - staticcheck
+      path: ^pkg/util/vhost/http\.go$
+      text: "^SA1019:"
     - linters:
       - errcheck
       - maligned

Release.md

@@ -1,3 +1,4 @@
 ## Fixes
 
 * Fixed control-session replacement leaks when frpc reconnects through a half-open TCP multiplexed connection.
+* Fixed an SSH tunnel gateway panic when handling malformed exec requests.

go.mod

@@ -5,7 +5,7 @@ go 1.25.0
 require (
 	github.com/armon/go-socks5 v0.0.0-20160902184237-e75332964ef5
 	github.com/coreos/go-oidc/v3 v3.14.1
-	github.com/fatedier/golib v0.7.2-0.20260715094513-2780ae1d8cdb
+	github.com/fatedier/golib v0.8.0
 	github.com/google/uuid v1.6.0
 	github.com/gorilla/mux v1.8.1
 	github.com/gorilla/websocket v1.5.0
@@ -25,11 +25,11 @@ require (
 	github.com/tidwall/gjson v1.17.1
 	github.com/vishvananda/netlink v1.3.0
 	github.com/xtaci/kcp-go/v5 v5.6.13
-	golang.org/x/crypto v0.49.0
+	golang.org/x/crypto v0.54.0
-	golang.org/x/net v0.52.0
+	golang.org/x/net v0.56.0
 	golang.org/x/oauth2 v0.28.0
-	golang.org/x/sync v0.20.0
+	golang.org/x/sync v0.22.0
-	golang.org/x/sys v0.42.0
+	golang.org/x/sys v0.47.0
 	golang.org/x/time v0.10.0
 	golang.zx2c4.com/wireguard v0.0.0-20231211153847-12269c276173
 	gopkg.in/ini.v1 v1.67.0
@@ -64,9 +64,9 @@ require (
 	github.com/tjfoc/gmsm v1.4.1 // indirect
 	github.com/vishvananda/netns v0.0.4 // indirect
 	go.uber.org/automaxprocs v1.6.0 // indirect
-	golang.org/x/mod v0.33.0 // indirect
+	golang.org/x/mod v0.37.0 // indirect
-	golang.org/x/text v0.35.0 // indirect
+	golang.org/x/text v0.40.0 // indirect
-	golang.org/x/tools v0.42.0 // indirect
+	golang.org/x/tools v0.47.0 // indirect
 	golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2 // indirect
 	google.golang.org/protobuf v1.36.5 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect

go.sum

@@ -20,8 +20,8 @@ github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSs
 github.com/envoyproxy/go-control-plane v0.9.0/go.mod h1:YTl/9mNaCwkRvm6d1a2C3ymFceY/DCBVvsKhRF0iEA4=
 github.com/envoyproxy/go-control-plane v0.9.4/go.mod h1:6rpuAdCZL397s3pYoYcLgu1mIlRU8Am5FuJP05cCM98=
 github.com/envoyproxy/protoc-gen-validate v0.1.0/go.mod h1:iSmxcyjqTsJpI2R4NaDN7+kN2VEUnK/pcBlmesArF7c=
-github.com/fatedier/golib v0.7.2-0.20260715094513-2780ae1d8cdb h1:6gcaE769mFb1G/cNV6lgzmwIYkNXmhj4pmcddllfmB4=
+github.com/fatedier/golib v0.8.0 h1:LQC8Mly/N71CUnFmgZMfQGrCA4h0tghg9pcDx58uG10=
-github.com/fatedier/golib v0.7.2-0.20260715094513-2780ae1d8cdb/go.mod h1:ArUGvPg2cOw/py2RAuBt46nNZH2VQ5Z70p109MAZpJw=
+github.com/fatedier/golib v0.8.0/go.mod h1:ArUGvPg2cOw/py2RAuBt46nNZH2VQ5Z70p109MAZpJw=
 github.com/fatedier/yamux v0.0.0-20250825093530-d0154be01cd6 h1:u92UUy6FURPmNsMBUuongRWC0rBqN6gd01Dzu+D21NE=
 github.com/fatedier/yamux v0.0.0-20250825093530-d0154be01cd6/go.mod h1:c5/tk6G0dSpXGzJN7Wk1OEie8grdSJAmeawId9Zvd34=
 github.com/go-jose/go-jose/v4 v4.0.5 h1:M6T8+mKZl/+fNNuFHvGIzDz7BTLQPIounk/b9dw3AaE=
@@ -149,30 +149,30 @@ go.uber.org/mock v0.5.2/go.mod h1:wLlUxC2vVTPTaE3UD51E0BGOAElKrILxhVSDYQLld5o=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/crypto v0.0.0-20201012173705-84dcc777aaee/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
-golang.org/x/crypto v0.49.0 h1:+Ng2ULVvLHnJ/ZFEq4KdcDd/cfjrrjjNSXNzxg0Y4U4=
+golang.org/x/crypto v0.54.0 h1:YLIA59K4fiNzHzjnZt2tUJQjQtUWfWbeHBqKtk3eScw=
-golang.org/x/crypto v0.49.0/go.mod h1:ErX4dUh2UM+CFYiXZRTcMpEcN8b/1gxEuv3nODoYtCA=
+golang.org/x/crypto v0.54.0/go.mod h1:KWL8ny2AZdGR2cWmzeHrp2azQPGogOv+HeQaVEXC2dk=
 golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
 golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
 golang.org/x/lint v0.0.0-20190227174305-5b3e6a55c961/go.mod h1:wehouNa3lNwaWXcvxsM5YxQ5yQlVC4a0KAMCusXpPoU=
 golang.org/x/lint v0.0.0-20190313153728-d0100b6bd8b3/go.mod h1:6SW0HCj/g11FgYtHlgUYUwCkIfeOF89ocIRzGO/8vkc=
-golang.org/x/mod v0.33.0 h1:tHFzIWbBifEmbwtGz65eaWyGiGZatSrT9prnU8DbVL8=
+golang.org/x/mod v0.37.0 h1:vF1DjpVEshcIqoEaauuHebaLk1O1forxjxBaVn884JQ=
-golang.org/x/mod v0.33.0/go.mod h1:swjeQEj+6r7fODbD2cqrnje9PnziFuw4bmLbBZFrQ5w=
+golang.org/x/mod v0.37.0/go.mod h1:m8S8VeM9r4dzDwjrKO0a1sZP3YjeMamRRlD+fmR2Q/0=
 golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20180826012351-8a410e7b638d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20190213061140-3a22650c66bd/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20190311183353-d8887717615a/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20201010224723-4f7140c49acb/go.mod h1:sp8m0HH+o8qH0wwXwYZr8TS3Oi6o0r6Gce1SSxlDquU=
-golang.org/x/net v0.52.0 h1:He/TN1l0e4mmR3QqHMT2Xab3Aj3L9qjbhRm78/6jrW0=
+golang.org/x/net v0.56.0 h1:Rw8j/hFzGvJUZwNBXnAtf5sVDVt+65SK2C7IxCxZt5o=
-golang.org/x/net v0.52.0/go.mod h1:R1MAz7uMZxVMualyPXb+VaqGSa3LIaUqk0eEt3w36Sw=
+golang.org/x/net v0.56.0/go.mod h1:D3Ku6r+V6JROoZK144D2XfMHFcMq/0zSfLelVTCFKec=
 golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
 golang.org/x/oauth2 v0.28.0 h1:CrgCKl8PPAVtLnU3c+EDw6x11699EWlsDeWNWKdIOkc=
 golang.org/x/oauth2 v0.28.0/go.mod h1:onh5ek6nERTohokkhCD/y2cV4Do3fxFHFuAejCkRWT8=
 golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20181108010431-42b317875d0f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sync v0.20.0 h1:e0PTpb7pjO8GAtTs2dQ6jYa5BWYlMuX047Dco/pItO4=
+golang.org/x/sync v0.22.0 h1:SZjpbeLmrCk4xhRSZFNZW5gFUeCeFgjekvI/+gfScek=
-golang.org/x/sync v0.20.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
+golang.org/x/sync v0.22.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
@@ -180,14 +180,14 @@ golang.org/x/sys v0.0.0-20200930185726-fdedc70b468f/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.2.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.10.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.42.0 h1:omrd2nAlyT5ESRdCLYdm3+fMfNFE/+Rf4bDIQImRJeo=
+golang.org/x/sys v0.47.0 h1:o7XGOvZQCADBQQ4Y7VNq2dRWQR7JmOUW8Kxx4ZsNgWs=
-golang.org/x/sys v0.42.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
+golang.org/x/sys v0.47.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
-golang.org/x/term v0.41.0 h1:QCgPso/Q3RTJx2Th4bDLqML4W6iJiaXFq2/ftQF13YU=
+golang.org/x/term v0.45.0 h1:NwWyBmoJCbfTHpxrWoZ9C6/VxOf7ic219I8xZZFdrf0=
-golang.org/x/term v0.41.0/go.mod h1:3pfBgksrReYfZ5lvYM0kSO0LIkAl4Yl2bXOkKP7Ec2A=
+golang.org/x/term v0.45.0/go.mod h1:9aqxs0blBcrm/n0L9QW0aRVD+ktan8ssZromtqJC43w=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
-golang.org/x/text v0.35.0 h1:JOVx6vVDFokkpaq1AEptVzLTpDe9KGpj5tR4/X+ybL8=
+golang.org/x/text v0.40.0 h1:Ub2Z6/xjgF1WrYQz2nuITOEegKFtiIy+rieRJ5lHZKs=
-golang.org/x/text v0.35.0/go.mod h1:khi/HExzZJ2pGnjenulevKNX1W67CUy0AsXcNubPGCA=
+golang.org/x/text v0.40.0/go.mod h1:hpnzDAfGV753zIKo+wk3u1bVKCGPbrnF7+7LBF/UHVY=
 golang.org/x/time v0.10.0 h1:3usCWA8tQn0L8+hFJQNgzpWbd89begxN66o1Ojdn5L4=
 golang.org/x/time v0.10.0/go.mod h1:3BpzKBy/shNhVucY/MWOyx10tF3SFh9QdLuxbVysPQM=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
@@ -195,8 +195,8 @@ golang.org/x/tools v0.0.0-20190114222345-bf090417da8b/go.mod h1:n7NCudcB/nEzxVGm
 golang.org/x/tools v0.0.0-20190226205152-f727befe758c/go.mod h1:9Yl7xja0Znq3iFh3HoIrodX9oNMXvdceNzlUR8zjMvY=
 golang.org/x/tools v0.0.0-20190311212946-11955173bddd/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
 golang.org/x/tools v0.0.0-20190524140312-2c0ae7006135/go.mod h1:RgjU9mgBXZiqYHBnxXauZ1Gv1EHHAz9KjViQ78xBX0Q=
-golang.org/x/tools v0.42.0 h1:uNgphsn75Tdz5Ji2q36v/nsFSfR/9BRFvqhGBaJGd5k=
+golang.org/x/tools v0.47.0 h1:7Kn5x/d1svx/PzryTsqeoZN4TZwqeH5pGWjefhLi/1Q=
-golang.org/x/tools v0.42.0/go.mod h1:Ma6lCIwGZvHK6XtgbswSoWroEkhugApmsXyrUmBhfr0=
+golang.org/x/tools v0.47.0/go.mod h1:dFHnyTvFWY212G+h7ZY4Vsp/K3U4/7W9TyVaAul8uCA=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2 h1:B82qJJgjvYKsXS9jeunTOisW56dUokqW/FOteYJJ/yg=
 golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2/go.mod h1:deeaetjYA+DHMHg+sMSMI58GrEteJUUzzw7en6TJQcI=

pkg/ssh/server.go

@@ -16,7 +16,6 @@ package ssh
 
 import (
 	"context"
-	"encoding/binary"
 	"errors"
 	"fmt"
 	"net"
@@ -52,6 +51,11 @@ type tcpipForward struct {
 	Port uint32
 }
 
+// https://datatracker.ietf.org/doc/html/rfc4254#section-6.5
+type execPayload struct {
+	Command string
+}
+
 // https://datatracker.ietf.org/doc/html/rfc4254#page-16
 type forwardedTCPPayload struct {
 	Addr string
@@ -309,14 +313,13 @@ func (s *TunnelServer) handleNewChannel(channel ssh.NewChannel, extraPayloadCh c
 		if req.WantReply {
 			_ = req.Reply(true, nil)
 		}
-		if req.Type != "exec" || len(req.Payload) <= 4 {
+		if req.Type != "exec" {
 			continue
 		}
-		end := 4 + binary.BigEndian.Uint32(req.Payload[:4])
+		extraPayload, ok := parseExecPayload(req.Payload)
-		if len(req.Payload) < int(end) {
+		if !ok {
 			continue
 		}
-		extraPayload := string(req.Payload[4:end])
 		select {
 		case extraPayloadCh <- extraPayload:
 		default:
@@ -324,6 +327,14 @@ func (s *TunnelServer) handleNewChannel(channel ssh.NewChannel, extraPayloadCh c
 	}
 }
 
+func parseExecPayload(payload []byte) (string, bool) {
+	var msg execPayload
+	if err := ssh.Unmarshal(payload, &msg); err != nil {
+		return "", false
+	}
+	return msg.Command, true
+}
+
 func (s *TunnelServer) keepAlive(ch ssh.Channel) {
 	tk := time.NewTicker(time.Second * 30)
 	defer tk.Stop()

pkg/ssh/server_test.go

@@ -0,0 +1,71 @@
+// Copyright 2026 The frp Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package ssh
+
+import (
+	"encoding/binary"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	cryptossh "golang.org/x/crypto/ssh"
+)
+
+func TestParseExecPayload(t *testing.T) {
+	payload := cryptossh.Marshal(&execPayload{Command: "tcp --remote_port 6000"})
+
+	got, ok := parseExecPayload(payload)
+
+	require.True(t, ok)
+	require.Equal(t, "tcp --remote_port 6000", got)
+}
+
+func TestParseExecPayloadRejectsMalformedPayloads(t *testing.T) {
+	overflowLength := make([]byte, 5)
+	binary.BigEndian.PutUint32(overflowLength[:4], ^uint32(0))
+
+	for _, tc := range []struct {
+		name    string
+		payload []byte
+	}{
+		{
+			name:    "empty",
+			payload: nil,
+		},
+		{
+			name:    "short length prefix",
+			payload: []byte{0, 0, 0},
+		},
+		{
+			name:    "declared length exceeds remaining payload",
+			payload: []byte{0, 0, 0, 2, 'x'},
+		},
+		{
+			name:    "overflow length",
+			payload: overflowLength,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			var (
+				got string
+				ok  bool
+			)
+			require.NotPanics(t, func() {
+				got, ok = parseExecPayload(tc.payload)
+			})
+			require.False(t, ok)
+			require.Empty(t, got)
+		})
+	}
+}

pkg/util/version/version.go

@@ -14,7 +14,7 @@
 
 package version
 
-var version = "0.70.0"
+var version = "0.70.1"
 
 func Full() string {
 	return version