Bump version

Fixes #3459

.github/setup_go_for_windows7.sh

@@ -1,25 +1,27 @@
 #!/usr/bin/env bash
 
-VERSION="1.23.12"
+VERSION="1.25.3"
 
 mkdir -p $HOME/go
 cd $HOME/go
 wget "https://dl.google.com/go/go${VERSION}.linux-amd64.tar.gz"
 tar -xzf "go${VERSION}.linux-amd64.tar.gz"
-mv go go_legacy
-cd go_legacy
+mv go go_win7
+cd go_win7
 
 # modify from https://github.com/restic/restic/issues/4636#issuecomment-1896455557
-# this patch file only works on golang1.23.x
-# that means after golang1.24 release it must be changed
-# see: https://github.com/MetaCubeX/go/commits/release-branch.go1.23/
+# this patch file only works on golang1.25.x
+# that means after golang1.26 release it must be changed
+# see: https://github.com/MetaCubeX/go/commits/release-branch.go1.25/
 # revert:
 # 693def151adff1af707d82d28f55dba81ceb08e1: "crypto/rand,runtime: switch RtlGenRandom for ProcessPrng"
 # 7c1157f9544922e96945196b47b95664b1e39108: "net: remove sysSocket fallback for Windows 7"
 # 48042aa09c2f878c4faa576948b07fe625c4707a: "syscall: remove Windows 7 console handle workaround"
 # a17d959debdb04cd550016a3501dd09d50cd62e7: "runtime: always use LoadLibraryEx to load system libraries"
 
-curl https://github.com/MetaCubeX/go/commit/9ac42137ef6730e8b7daca016ece831297a1d75b.diff | patch --verbose -p 1
-curl https://github.com/MetaCubeX/go/commit/21290de8a4c91408de7c2b5b68757b1e90af49dd.diff | patch --verbose -p 1
-curl https://github.com/MetaCubeX/go/commit/6a31d3fa8e47ddabc10bd97bff10d9a85f4cfb76.diff | patch --verbose -p 1
-curl https://github.com/MetaCubeX/go/commit/69e2eed6dd0f6d815ebf15797761c13f31213dd6.diff | patch --verbose -p 1
+alias curl='curl -H "Authorization: Bearer ${{ secrets.GITHUB_TOKEN }}"'
+
+curl https://github.com/MetaCubeX/go/commit/8cb5472d94c34b88733a81091bd328e70ee565a4.diff | patch --verbose -p 1
+curl https://github.com/MetaCubeX/go/commit/6788c4c6f9fafb56729bad6b660f7ee2272d699f.diff | patch --verbose -p 1
+curl https://github.com/MetaCubeX/go/commit/a5b2168bb836ed9d6601c626f95e56c07923f906.diff | patch --verbose -p 1
+curl https://github.com/MetaCubeX/go/commit/f56f1e23507e646c85243a71bde7b9629b2f970c.diff | patch --verbose -p 1

.github/workflows/build.yml

@@ -46,7 +46,7 @@ jobs:
       - name: Setup Go
         uses: actions/setup-go@v5
         with:
-          go-version: ^1.25.1
+          go-version: ^1.25.3
       - name: Check input version
         if: github.event_name == 'workflow_dispatch'
         run: |-
@@ -88,9 +88,9 @@ jobs:
           - { os: linux, arch: loong64, debian: loongarch64, rpm: loongarch64, openwrt: "loongarch64_generic" }
 
           - { os: windows, arch: amd64 }
-          - { os: windows, arch: amd64, legacy_go123: true, legacy_name: "windows-7" }
+          - { os: windows, arch: amd64, legacy_win7: true, legacy_name: "windows-7" }
           - { os: windows, arch: "386" }
-          - { os: windows, arch: "386", legacy_go123: true, legacy_name: "windows-7" }
+          - { os: windows, arch: "386", legacy_win7: true, legacy_name: "windows-7" }
           - { os: windows, arch: arm64 }
 
           - { os: darwin, arch: amd64 }
@@ -110,29 +110,29 @@ jobs:
         if: ${{ ! (matrix.legacy_go123 || matrix.legacy_go124) }}
         uses: actions/setup-go@v5
         with:
-          go-version: ^1.25.1
+          go-version: ^1.25.3
       - name: Setup Go 1.24
         if: matrix.legacy_go124
         uses: actions/setup-go@v5
         with:
           go-version: ~1.24.6
-      - name: Cache Go 1.23
-        if: matrix.legacy_go123
-        id: cache-legacy-go
+      - name: Cache Go for Windows 7
+        if: matrix.legacy_win7
+        id: cache-go-for-windows7
         uses: actions/cache@v4
         with:
           path: |
-            ~/go/go_legacy
-          key: go_legacy_12312
-      - name: Setup Go 1.23
-        if: matrix.legacy_go123 && steps.cache-legacy-go.outputs.cache-hit != 'true'
+            ~/go/go_win7
+          key: go_win7_1253
+      - name: Setup Go for Windows 7
+        if: matrix.legacy_win7 && steps.cache-go-for-windows7.outputs.cache-hit != 'true'
         run: |-
-          .github/setup_legacy_go.sh
-      - name: Setup Go 1.23
-        if: matrix.legacy_go123
+          .github/setup_go_for_windows7.sh
+      - name: Setup Go for Windows 7
+        if: matrix.legacy_win7
         run: |-
-          echo "PATH=$HOME/go/go_legacy/bin:$PATH" >> $GITHUB_ENV
-          echo "GOROOT=$HOME/go/go_legacy" >> $GITHUB_ENV
+          echo "PATH=$HOME/go/go_win7/bin:$PATH" >> $GITHUB_ENV
+          echo "GOROOT=$HOME/go/go_win7" >> $GITHUB_ENV
       - name: Setup Android NDK
         if: matrix.os == 'android'
         uses: nttld/setup-ndk@v1
@@ -300,7 +300,7 @@ jobs:
       - name: Setup Go
         uses: actions/setup-go@v5
         with:
-          go-version: ^1.25.1
+          go-version: ^1.25.3
       - name: Setup Android NDK
         id: setup-ndk
         uses: nttld/setup-ndk@v1
@@ -380,7 +380,7 @@ jobs:
       - name: Setup Go
         uses: actions/setup-go@v5
         with:
-          go-version: ^1.25.1
+          go-version: ^1.25.3
       - name: Setup Android NDK
         id: setup-ndk
         uses: nttld/setup-ndk@v1
@@ -479,7 +479,7 @@ jobs:
         if: matrix.if
         uses: actions/setup-go@v5
         with:
-          go-version: ^1.25.1
+          go-version: ^1.25.3
       - name: Set tag
         if: matrix.if
         run: |-

.github/workflows/linux.yml

@@ -30,7 +30,7 @@ jobs:
       - name: Setup Go
         uses: actions/setup-go@v5
         with:
-          go-version: ^1.25.1
+          go-version: ^1.25.3
       - name: Check input version
         if: github.event_name == 'workflow_dispatch'
         run: |-
@@ -71,7 +71,7 @@ jobs:
       - name: Setup Go
         uses: actions/setup-go@v5
         with:
-          go-version: ^1.25.1
+          go-version: ^1.25.3
       - name: Setup Android NDK
         if: matrix.os == 'android'
         uses: nttld/setup-ndk@v1

.gitignore

@@ -15,5 +15,6 @@
 .DS_Store
 /config.d/
 /venv/
-!/README.md
-/*.md
+CLAUDE.md
+AGENTS.md
+/.claude/

common/tls/client.go

@@ -53,26 +53,48 @@ func ClientHandshake(ctx context.Context, conn net.Conn, config Config) (Conn, e
 	return tlsConn, nil
 }
 
-type Dialer struct {
+type Dialer interface {
+	N.Dialer
+	DialTLSContext(ctx context.Context, destination M.Socksaddr) (Conn, error)
+}
+
+type defaultDialer struct {
 	dialer N.Dialer
 	config Config
 }
 
-func NewDialer(dialer N.Dialer, config Config) N.Dialer {
-	return &Dialer{dialer, config}
+func NewDialer(dialer N.Dialer, config Config) Dialer {
+	return &defaultDialer{dialer, config}
 }
 
-func (d *Dialer) DialContext(ctx context.Context, network string, destination M.Socksaddr) (net.Conn, error) {
-	if network != N.NetworkTCP {
+func (d *defaultDialer) DialContext(ctx context.Context, network string, destination M.Socksaddr) (net.Conn, error) {
+	if N.NetworkName(network) != N.NetworkTCP {
 		return nil, os.ErrInvalid
 	}
-	conn, err := d.dialer.DialContext(ctx, network, destination)
+	return d.DialTLSContext(ctx, destination)
+}
+
+func (d *defaultDialer) ListenPacket(ctx context.Context, destination M.Socksaddr) (net.PacketConn, error) {
+	return nil, os.ErrInvalid
+}
+
+func (d *defaultDialer) DialTLSContext(ctx context.Context, destination M.Socksaddr) (Conn, error) {
+	return d.dialContext(ctx, destination)
+}
+
+func (d *defaultDialer) dialContext(ctx context.Context, destination M.Socksaddr) (Conn, error) {
+	conn, err := d.dialer.DialContext(ctx, N.NetworkTCP, destination)
 	if err != nil {
 		return nil, err
 	}
-	return ClientHandshake(ctx, conn, d.config)
+	tlsConn, err := aTLS.ClientHandshake(ctx, conn, d.config)
+	if err != nil {
+		conn.Close()
+		return nil, err
+	}
+	return tlsConn, nil
 }
 
-func (d *Dialer) ListenPacket(ctx context.Context, destination M.Socksaddr) (net.PacketConn, error) {
-	return nil, os.ErrInvalid
+func (d *defaultDialer) Upstream() any {
+	return d.dialer
 }

dns/client.go

@@ -95,6 +95,20 @@ func (c *Client) Start() {
 	}
 }
 
+func extractNegativeTTL(response *dns.Msg) (uint32, bool) {
+	for _, record := range response.Ns {
+		if soa, isSOA := record.(*dns.SOA); isSOA {
+			soaTTL := soa.Header().Ttl
+			soaMinimum := soa.Minttl
+			if soaTTL < soaMinimum {
+				return soaTTL, true
+			}
+			return soaMinimum, true
+		}
+	}
+	return 0, false
+}
+
 func (c *Client) Exchange(ctx context.Context, transport adapter.DNSTransport, message *dns.Msg, options adapter.DNSQueryOptions, responseChecker func(responseAddrs []netip.Addr) bool) (*dns.Msg, error) {
 	if len(message.Question) == 0 {
 		if c.logger != nil {
@@ -214,7 +228,7 @@ func (c *Client) Exchange(ctx context.Context, transport adapter.DNSTransport, m
 			response.Answer = append(response.Answer, validResponse.Answer...)
 		}
 	}*/
-	disableCache = disableCache || response.Rcode != dns.RcodeSuccess || len(response.Answer) == 0
+	disableCache = disableCache || (response.Rcode != dns.RcodeSuccess && response.Rcode != dns.RcodeNameError)
 	if responseChecker != nil {
 		var rejected bool
 		// TODO: add accept_any rule and support to check response instead of addresses
@@ -251,10 +265,17 @@ func (c *Client) Exchange(ctx context.Context, transport adapter.DNSTransport, m
 		}
 	}
 	var timeToLive uint32
-	for _, recordList := range [][]dns.RR{response.Answer, response.Ns, response.Extra} {
-		for _, record := range recordList {
-			if timeToLive == 0 || record.Header().Ttl > 0 && record.Header().Ttl < timeToLive {
-				timeToLive = record.Header().Ttl
+	if len(response.Answer) == 0 {
+		if soaTTL, hasSOA := extractNegativeTTL(response); hasSOA {
+			timeToLive = soaTTL
+		}
+	}
+	if timeToLive == 0 {
+		for _, recordList := range [][]dns.RR{response.Answer, response.Ns, response.Extra} {
+			for _, record := range recordList {
+				if timeToLive == 0 || record.Header().Ttl > 0 && record.Header().Ttl < timeToLive {
+					timeToLive = record.Header().Ttl
+				}
 			}
 		}
 	}
@@ -364,14 +385,18 @@ func (c *Client) LookupCache(domain string, strategy C.DomainStrategy) ([]netip.
 			Qtype:  dns.TypeA,
 			Qclass: dns.ClassINET,
 		}, nil)
+		if response4 == nil {
+			return nil, false
+		}
 		response6, _ := c.loadResponse(dns.Question{
 			Name:   dnsName,
 			Qtype:  dns.TypeAAAA,
 			Qclass: dns.ClassINET,
 		}, nil)
-		if response4 != nil || response6 != nil {
-			return sortAddresses(MessageToAddresses(response4), MessageToAddresses(response6), strategy), true
+		if response6 == nil {
+			return nil, false
 		}
+		return sortAddresses(MessageToAddresses(response4), MessageToAddresses(response6), strategy), true
 	}
 	return nil, false
 }

dns/router.go

@@ -386,12 +386,7 @@ func (r *Router) Lookup(ctx context.Context, domain string, options adapter.DNSQ
 			if rule != nil {
 				switch action := rule.Action().(type) {
 				case *R.RuleActionReject:
-					switch action.Method {
-					case C.RuleActionRejectMethodDefault:
-						return nil, nil
-					case C.RuleActionRejectMethodDrop:
-						return nil, tun.ErrDrop
-					}
+					return nil, &R.RejectedError{Cause: action.Error(ctx)}
 				case *R.RuleActionPredefined:
 					if action.Rcode != mDNS.RcodeSuccess {
 						err = RcodeError(action.Rcode)

dns/transport/https.go

@@ -25,7 +25,6 @@ import (
 	"github.com/sagernet/sing/common/logger"
 	M "github.com/sagernet/sing/common/metadata"
 	N "github.com/sagernet/sing/common/network"
-	aTLS "github.com/sagernet/sing/common/tls"
 	sHTTP "github.com/sagernet/sing/protocol/http"
 
 	mDNS "github.com/miekg/dns"
@@ -47,7 +46,7 @@ type HTTPSTransport struct {
 	destination      *url.URL
 	headers          http.Header
 	transportAccess  sync.Mutex
-	transport        *http.Transport
+	transport        *HTTPSTransportWrapper
 	transportResetAt time.Time
 }
 
@@ -62,11 +61,8 @@ func NewHTTPS(ctx context.Context, logger log.ContextLogger, tag string, options
 	if err != nil {
 		return nil, err
 	}
-	if common.Error(tlsConfig.Config()) == nil && !common.Contains(tlsConfig.NextProtos(), http2.NextProtoTLS) {
-		tlsConfig.SetNextProtos(append(tlsConfig.NextProtos(), http2.NextProtoTLS))
-	}
-	if !common.Contains(tlsConfig.NextProtos(), "http/1.1") {
-		tlsConfig.SetNextProtos(append(tlsConfig.NextProtos(), "http/1.1"))
+	if len(tlsConfig.NextProtos()) == 0 {
+		tlsConfig.SetNextProtos([]string{http2.NextProtoTLS, "http/1.1"})
 	}
 	headers := options.Headers.Build()
 	host := headers.Get("Host")
@@ -124,37 +120,13 @@ func NewHTTPSRaw(
 	serverAddr M.Socksaddr,
 	tlsConfig tls.Config,
 ) *HTTPSTransport {
-	var transport *http.Transport
-	if tlsConfig != nil {
-		transport = &http.Transport{
-			ForceAttemptHTTP2: true,
-			DialTLSContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
-				tcpConn, hErr := dialer.DialContext(ctx, network, serverAddr)
-				if hErr != nil {
-					return nil, hErr
-				}
-				tlsConn, hErr := aTLS.ClientHandshake(ctx, tcpConn, tlsConfig)
-				if hErr != nil {
-					tcpConn.Close()
-					return nil, hErr
-				}
-				return tlsConn, nil
-			},
-		}
-	} else {
-		transport = &http.Transport{
-			DialContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
-				return dialer.DialContext(ctx, network, serverAddr)
-			},
-		}
-	}
 	return &HTTPSTransport{
 		TransportAdapter: adapter,
 		logger:           logger,
 		dialer:           dialer,
 		destination:      destination,
 		headers:          headers,
-		transport:        transport,
+		transport:        NewHTTPSTransportWrapper(tls.NewDialer(dialer, tlsConfig), serverAddr),
 	}
 }
 

dns/transport/https_transport.go

@@ -0,0 +1,80 @@
+package transport
+
+import (
+	"context"
+	"errors"
+	"net"
+	"net/http"
+	"sync/atomic"
+
+	"github.com/sagernet/sing-box/common/tls"
+	E "github.com/sagernet/sing/common/exceptions"
+	M "github.com/sagernet/sing/common/metadata"
+
+	"golang.org/x/net/http2"
+)
+
+var errFallback = E.New("fallback to HTTP/1.1")
+
+type HTTPSTransportWrapper struct {
+	http2Transport *http2.Transport
+	httpTransport  *http.Transport
+	fallback       *atomic.Bool
+}
+
+func NewHTTPSTransportWrapper(dialer tls.Dialer, serverAddr M.Socksaddr) *HTTPSTransportWrapper {
+	var fallback atomic.Bool
+	return &HTTPSTransportWrapper{
+		http2Transport: &http2.Transport{
+			DialTLSContext: func(ctx context.Context, _, _ string, _ *tls.STDConfig) (net.Conn, error) {
+				tlsConn, err := dialer.DialTLSContext(ctx, serverAddr)
+				if err != nil {
+					return nil, err
+				}
+				state := tlsConn.ConnectionState()
+				if state.NegotiatedProtocol == http2.NextProtoTLS {
+					return tlsConn, nil
+				}
+				tlsConn.Close()
+				fallback.Store(true)
+				return nil, errFallback
+			},
+		},
+		httpTransport: &http.Transport{
+			DialTLSContext: func(ctx context.Context, _, _ string) (net.Conn, error) {
+				return dialer.DialTLSContext(ctx, serverAddr)
+			},
+		},
+		fallback: &fallback,
+	}
+}
+
+func (h *HTTPSTransportWrapper) RoundTrip(request *http.Request) (*http.Response, error) {
+	if h.fallback.Load() {
+		return h.httpTransport.RoundTrip(request)
+	} else {
+		response, err := h.http2Transport.RoundTrip(request)
+		if err != nil {
+			if errors.Is(err, errFallback) {
+				return h.httpTransport.RoundTrip(request)
+			}
+			return nil, err
+		}
+		return response, nil
+	}
+}
+
+func (h *HTTPSTransportWrapper) CloseIdleConnections() {
+	h.http2Transport.CloseIdleConnections()
+	h.httpTransport.CloseIdleConnections()
+}
+
+func (h *HTTPSTransportWrapper) Clone() *HTTPSTransportWrapper {
+	return &HTTPSTransportWrapper{
+		httpTransport: h.httpTransport,
+		http2Transport: &http2.Transport{
+			DialTLSContext: h.http2Transport.DialTLSContext,
+		},
+		fallback: h.fallback,
+	}
+}

docs/changelog.md

@@ -2,6 +2,16 @@
 icon: material/alert-decagram
 ---
 
+#### 1.12.10
+
+* Update uTLS to v1.8.1 **1**
+* Fixes and improvements
+
+**1**:
+
+This update fixes an critical issue that could cause simulated Chrome fingerprints to be detected,
+see https://github.com/refraction-networking/utls/pull/375.
+
 #### 1.12.9
 
 * Fixes and improvements
@@ -96,7 +106,8 @@ See [Tailscale](/configuration/endpoint/tailscale/).
 
 Due to maintenance difficulties, sing-box 1.12.0 requires at least Go 1.23 to compile.
 
-For Windows 7 users, legacy binaries now continue to compile with Go 1.23 and patches from [MetaCubeX/go](https://github.com/MetaCubeX/go).
+For Windows 7 users, legacy binaries now continue to compile with Go 1.23 and patches
+from [MetaCubeX/go](https://github.com/MetaCubeX/go).
 
 **7**:
 
@@ -158,7 +169,8 @@ See [Tun](/configuration/inbound/tun/#loopback_address).
 
 We have significantly improved the performance of tun inbound on Apple platforms, especially in the gVisor stack.
 
-The following data was tested using [tun_bench](https://github.com/SagerNet/sing-box/blob/dev-next/cmd/internal/tun_bench/main.go) on M4 MacBook pro.
+The following data was tested
+using [tun_bench](https://github.com/SagerNet/sing-box/blob/dev-next/cmd/internal/tun_bench/main.go) on M4 MacBook pro.
 
 | Version     | Stack  | MTU   | Upload | Download |
 |-------------|--------|-------|--------|----------|
@@ -177,8 +189,8 @@ The following data was tested using [tun_bench](https://github.com/SagerNet/sing
 
 **18**:
 
-We continue to experience issues updating our sing-box apps on the App Store and Play Store. 
-Until we rewrite and resubmit the apps, they are considered irrecoverable. 
+We continue to experience issues updating our sing-box apps on the App Store and Play Store.
+Until we rewrite and resubmit the apps, they are considered irrecoverable.
 Therefore, after this release, we will not be repeating this notice unless there is new information.
 
 ### 1.11.15
@@ -459,7 +471,8 @@ See [AnyTLS Inbound](/configuration/inbound/anytls/) and [AnyTLS Outbound](/conf
 
 **2**:
 
-`resolve` route action now accepts `disable_cache` and other options like in DNS route actions, see [Route Action](/configuration/route/rule_action).
+`resolve` route action now accepts `disable_cache` and other options like in DNS route actions,
+see [Route Action](/configuration/route/rule_action).
 
 **3**:
 
@@ -490,7 +503,8 @@ See [Tailscale](/configuration/endpoint/tailscale/).
 
 Due to maintenance difficulties, sing-box 1.12.0 requires at least Go 1.23 to compile.
 
-For Windows 7 users, legacy binaries now continue to compile with Go 1.23 and patches from [MetaCubeX/go](https://github.com/MetaCubeX/go).
+For Windows 7 users, legacy binaries now continue to compile with Go 1.23 and patches
+from [MetaCubeX/go](https://github.com/MetaCubeX/go).
 
 ### 1.11.3
 

go.mod

@@ -16,7 +16,7 @@ require (
 	github.com/libdns/cloudflare v0.2.2-0.20250708034226-c574dccb31a6
 	github.com/logrusorgru/aurora v2.0.3+incompatible
 	github.com/metacubex/tfo-go v0.0.0-20250516165257-e29c16ae41d4
-	github.com/metacubex/utls v1.8.0
+	github.com/metacubex/utls v1.8.2
 	github.com/mholt/acmez/v3 v3.1.2
 	github.com/miekg/dns v1.1.67
 	github.com/oschwald/maxminddb-golang v1.13.1

go.sum

@@ -126,6 +126,8 @@ github.com/metacubex/tfo-go v0.0.0-20250516165257-e29c16ae41d4 h1:j1VRTiC9JLR4nU
 github.com/metacubex/tfo-go v0.0.0-20250516165257-e29c16ae41d4/go.mod h1:l9oLnLoEXyGZ5RVLsh7QCC5XsouTUyKk4F2nLm2DHLw=
 github.com/metacubex/utls v1.8.0 h1:mSYi6FMnmc5riARl5UZDmWVy710z+P5b7xuGW0lV9ac=
 github.com/metacubex/utls v1.8.0/go.mod h1:FdjYzVfCtgtna19hX0ER1Xsa5uJInwdQ4IcaaI98lEQ=
+github.com/metacubex/utls v1.8.2 h1:d7KalMZ5hnOJ6lThMz8Ykd+5dvmXH3Eoeyfv2jUuG3w=
+github.com/metacubex/utls v1.8.2/go.mod h1:kncGGVhFaoGn5M3pFe3SXhZCzsbCJayNOH4UEqTKTko=
 github.com/mholt/acmez/v3 v3.1.2 h1:auob8J/0FhmdClQicvJvuDavgd5ezwLBfKuYmynhYzc=
 github.com/mholt/acmez/v3 v3.1.2/go.mod h1:L1wOU06KKvq7tswuMDwKdcHeKpFFgkppZy/y0DFxagQ=
 github.com/miekg/dns v1.1.67 h1:kg0EHj0G4bfT5/oOys6HhZw4vmMlnoZ+gDu8tJ/AlI0=

protocol/anytls/outbound.go

@@ -13,6 +13,7 @@ import (
 	"github.com/sagernet/sing-box/log"
 	"github.com/sagernet/sing-box/option"
 	"github.com/sagernet/sing/common"
+	E "github.com/sagernet/sing/common/exceptions"
 	M "github.com/sagernet/sing/common/metadata"
 	N "github.com/sagernet/sing/common/network"
 	"github.com/sagernet/sing/common/uot"
@@ -43,6 +44,13 @@ func NewOutbound(ctx context.Context, router adapter.Router, logger log.ContextL
 	if options.TLS == nil || !options.TLS.Enabled {
 		return nil, C.ErrTLSRequired
 	}
+	// TCP Fast Open is incompatible with anytls because TFO creates a lazy connection
+	// that only establishes on first write. The lazy connection returns an empty address
+	// before establishment, but anytls SOCKS wrapper tries to access the remote address
+	// during handshake, causing a null pointer dereference crash.
+	if options.DialerOptions.TCPFastOpen {
+		return nil, E.New("tcp_fast_open is not supported with anytls outbound")
+	}
 
 	tlsConfig, err := tls.NewClient(ctx, options.Server, common.PtrValueOrDefault(options.TLS))
 	if err != nil {