Authorize daemon IPC callers by their local identity

client/internal/daemonaddr/owner.go

@@ -0,0 +1,15 @@
+package daemonaddr
+
+// DaemonRunsAsSelf reports whether the daemon listening at addr runs as this very
+// user. That is what makes an unprivileged daemon authorize this process for the
+// changes it otherwise restricts to root or an administrator, so a client can tell
+// up front whether those controls are usable instead of letting a save fail.
+//
+// It is answered from the ownership of the socket or pipe the daemon created, so it
+// costs no round trip and needs no cooperation from the daemon. Ownership that
+// cannot be read is reported as false, including for a TCP address, so a caller
+// reading this as "the daemon would allow it" fails closed. The daemon remains the
+// only thing that authorizes anything: this only decides what a client offers.
+func DaemonRunsAsSelf(addr string) bool {
+	return daemonRunsAsSelf(addr)
+}

client/internal/daemonaddr/owner_unix.go

@@ -0,0 +1,40 @@
+//go:build !windows
+
+package daemonaddr
+
+import (
+	"os"
+	"strings"
+	"syscall"
+
+	log "github.com/sirupsen/logrus"
+)
+
+// daemonRunsAsSelf compares the owner of the daemon's Unix socket with this
+// process's uid. Root is not treated specially here: a root caller is privileged
+// on its own merits, and a root-owned socket says nothing about the caller.
+func daemonRunsAsSelf(addr string) bool {
+	path, ok := strings.CutPrefix(addr, "unix://")
+	if !ok {
+		return false
+	}
+
+	info, err := os.Stat(path)
+	if err != nil {
+		log.Debugf("stat daemon socket %s: %v", path, err)
+		return false
+	}
+
+	// Only a socket says anything about a daemon. A directory or a leftover
+	// regular file at that path is not one, and reading it as "the daemon runs as
+	// us" would offer controls the daemon then refuses.
+	if info.Mode()&os.ModeSocket == 0 {
+		return false
+	}
+
+	stat, ok := info.Sys().(*syscall.Stat_t)
+	if !ok {
+		return false
+	}
+	return stat.Uid == uint32(os.Getuid())
+}

client/internal/daemonaddr/owner_unix_test.go

@@ -0,0 +1,62 @@
+//go:build !windows
+
+package daemonaddr
+
+import (
+	"net"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// A socket this user created means the daemon runs as this user, which is the
+// rootless case where the daemon delegates its authority to its own identity.
+func TestDaemonRunsAsSelf_OwnSocket(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "netbird.sock")
+	ln, err := net.Listen("unix", path)
+	if err != nil {
+		t.Fatalf("listen: %v", err)
+	}
+	t.Cleanup(func() {
+		if err := ln.Close(); err != nil {
+			t.Logf("close listener: %v", err)
+		}
+	})
+
+	if !DaemonRunsAsSelf("unix://" + path) {
+		t.Error("a socket owned by this user must count as the daemon running as us")
+	}
+}
+
+// Everything that is not a readable socket of ours has to answer false, because
+// the caller reads a true as "the daemon would authorize me".
+func TestDaemonRunsAsSelf_FailsClosed(t *testing.T) {
+	dir := t.TempDir()
+
+	// A socket owned by another user, which is what a root-run daemon looks like
+	// to an unprivileged client. Only assertable when we are not root ourselves.
+	rootOwned := "unix:///var/run/netbird.sock"
+	if _, err := os.Stat("/var/run/netbird.sock"); err == nil && os.Getuid() != 0 {
+		if DaemonRunsAsSelf(rootOwned) {
+			t.Error("a socket owned by another user must not count as ours")
+		}
+	}
+
+	for name, addr := range map[string]string{
+		"missing socket":  "unix://" + filepath.Join(dir, "absent.sock"),
+		"tcp address":     "tcp://127.0.0.1:41731",
+		"named pipe":      "npipe://netbird",
+		"empty":           "",
+		"no scheme":       filepath.Join(dir, "absent.sock"),
+		"directory":       "unix://" + dir,
+		"unknown scheme":  "http://localhost:8080",
+		"scheme only":     "unix://",
+		"relative socket": "unix://netbird.sock",
+	} {
+		t.Run(name, func(t *testing.T) {
+			if DaemonRunsAsSelf(addr) {
+				t.Errorf("%q must not count as a daemon running as us", addr)
+			}
+		})
+	}
+}

client/internal/daemonaddr/owner_windows.go

@@ -0,0 +1,42 @@
+//go:build windows
+
+package daemonaddr
+
+import (
+	"context"
+	"strings"
+
+	log "github.com/sirupsen/logrus"
+
+	"github.com/netbirdio/netbird/client/internal/ipcauth"
+)
+
+// daemonRunsAsSelf reads the owner of the daemon's pipe. A daemon running as the
+// service account owns its pipe as LocalSystem, and an elevated one as
+// BUILTIN\Administrators, so only a daemon the user started themselves matches.
+func daemonRunsAsSelf(addr string) bool {
+	name, ok := strings.CutPrefix(addr, pipeScheme)
+	if !ok {
+		return false
+	}
+
+	for _, path := range PipePaths(name) {
+		// Bounded: this runs on the UI's path for deciding which controls to
+		// offer, so a pipe that does not answer promptly must not stall it. A
+		// timeout leaves the caller unprivileged, which only disables controls.
+		ctx, cancel := context.WithTimeout(context.Background(), probeTimeout)
+		conn, err := dialPipe(ctx, path)
+		cancel()
+		if err != nil {
+			continue
+		}
+
+		owned := ipcauth.PipeOwnedBySelf(conn)
+		if cerr := conn.Close(); cerr != nil {
+			log.Debugf("close daemon pipe %s after ownership check: %v", path, cerr)
+		}
+		return owned
+	}
+
+	return false
+}

client/internal/daemonaddr/pipe.go

@@ -0,0 +1,103 @@
+package daemonaddr
+
+import (
+	"context"
+	"net"
+	"runtime"
+	"strings"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+)
+
+const (
+	// WindowsPipeAddr is the default daemon address on Windows. A named pipe
+	// carries the connecting process's token, which loopback TCP does not, so
+	// it is the only Windows transport on which the daemon can tell who is
+	// calling it.
+	WindowsPipeAddr = "npipe://netbird"
+
+	// legacyWindowsAddr is the loopback-TCP address the Windows daemon used
+	// before named-pipe support.
+	legacyWindowsAddr = "tcp://127.0.0.1:41731"
+
+	pipeScheme = "npipe://"
+
+	// protectedPrefix is the NPFS namespace in which only LocalSystem and
+	// members of BUILTIN\Administrators may create a pipe. A daemon running as
+	// the service account creates its pipe there so that an unprivileged process
+	// cannot pre-create the name, which would keep the daemon from starting and
+	// leave callers talking to the squatter. Opening such a pipe needs no
+	// privilege, so unprivileged clients still reach the daemon.
+	protectedPrefix = `ProtectedPrefix\Administrators\`
+)
+
+// DialTarget returns the gRPC dial target and transport options for a daemon
+// address. The npipe scheme needs a context dialer because gRPC has no
+// named-pipe resolver; unix and tcp are handled by gRPC itself.
+func DialTarget(addr string) (string, []grpc.DialOption) {
+	opts := []grpc.DialOption{grpc.WithTransportCredentials(insecure.NewCredentials())}
+
+	if name, ok := strings.CutPrefix(addr, pipeScheme); ok {
+		paths := PipePaths(name)
+		opts = append(opts, grpc.WithContextDialer(func(ctx context.Context, _ string) (net.Conn, error) {
+			return dialPipePaths(ctx, paths)
+		}))
+		return "passthrough:///netbird-daemon-pipe", opts
+	}
+
+	return strings.TrimPrefix(addr, "tcp://"), opts
+}
+
+// PipePath maps an npipe address name ("netbird", from "npipe://netbird") to a
+// Windows named-pipe path (\\.\pipe\netbird). A fully qualified path is left as
+// is.
+func PipePath(name string) string {
+	if strings.HasPrefix(name, `\\`) {
+		return name
+	}
+	return `\\.\pipe\` + name
+}
+
+// PipePaths returns the paths a daemon control pipe may live at for an npipe
+// address name, in the order both sides must try them: the protected name first,
+// then the plain one.
+//
+// The daemon serves the first it can create, which is the protected name when it
+// runs as the service account and the plain one when it runs as an ordinary user,
+// as it does in netstack mode. Clients therefore have to try both, and because a
+// client cannot tell from the name alone who created the pipe, the plain name is
+// only usable once the server's identity has been checked: see
+// verifyPipeServer.
+//
+// A fully qualified path is what the operator asked for and is used as is.
+func PipePaths(name string) []string {
+	if strings.HasPrefix(name, `\\`) {
+		return []string{name}
+	}
+	return []string{PipePath(protectedPrefix + name), PipePath(name)}
+}
+
+// IsProtectedPipePath reports whether a pipe path is in the namespace only an
+// administrator or LocalSystem can create in, which is what lets a client trust
+// such a pipe from its name alone.
+func IsProtectedPipePath(path string) bool {
+	return strings.HasPrefix(path, `\\.\pipe\`+protectedPrefix)
+}
+
+// MigrateLegacy upgrades the pre-named-pipe Windows daemon address to the named
+// pipe, reporting whether it rewrote the address. Existing installs persist the
+// daemon address, so without this an upgraded daemon would keep listening on
+// loopback TCP, where callers carry no identity and privileged operations would
+// have to be refused for everyone. Only the exact legacy default is rewritten:
+// a deliberately chosen custom address is left alone.
+func MigrateLegacy(addr string) (string, bool) {
+	return migrateLegacyForOS(runtime.GOOS, addr)
+}
+
+func migrateLegacyForOS(goos, addr string) (string, bool) {
+	if goos == "windows" && addr == legacyWindowsAddr {
+		return WindowsPipeAddr, true
+	}
+	return addr, false
+}

client/internal/daemonaddr/pipe_other.go

@@ -0,0 +1,15 @@
+//go:build !windows
+
+package daemonaddr
+
+import (
+	"context"
+	"fmt"
+	"net"
+)
+
+// dialPipePaths is Windows-only: no other platform serves the daemon on a named
+// pipe.
+func dialPipePaths(context.Context, []string) (net.Conn, error) {
+	return nil, fmt.Errorf("named pipes are only supported on Windows")
+}

client/internal/daemonaddr/pipe_test.go

@@ -0,0 +1,30 @@
+package daemonaddr
+
+import (
+	"slices"
+	"testing"
+)
+
+// The protected name must be tried before the plain one on both sides: it is the
+// one an unprivileged process cannot create, so preferring it is what keeps a
+// squatter from owning the name the service daemon would otherwise use.
+func TestPipePaths_PrefersTheProtectedName(t *testing.T) {
+	got := PipePaths("netbird")
+	want := []string{
+		`\\.\pipe\ProtectedPrefix\Administrators\netbird`,
+		`\\.\pipe\netbird`,
+	}
+	if !slices.Equal(got, want) {
+		t.Errorf("PipePaths = %q, want %q", got, want)
+	}
+}
+
+// An operator who passes a full path chose exactly one pipe, so neither side may
+// look anywhere else.
+func TestPipePaths_QualifiedPathIsUsedAsIs(t *testing.T) {
+	path := `\\.\pipe\custom-netbird`
+	got := PipePaths(path)
+	if !slices.Equal(got, []string{path}) {
+		t.Errorf("PipePaths = %q, want just %q", got, path)
+	}
+}

client/internal/daemonaddr/pipe_windows.go

@@ -0,0 +1,59 @@
+//go:build windows
+
+package daemonaddr
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+
+	"github.com/Microsoft/go-winio"
+	log "github.com/sirupsen/logrus"
+	"golang.org/x/sys/windows"
+
+	"github.com/netbirdio/netbird/client/internal/ipcauth"
+)
+
+// dialPipePaths connects to the first path that answers with a pipe server this
+// client may trust, and returns the last error when none does.
+func dialPipePaths(ctx context.Context, paths []string) (net.Conn, error) {
+	var lastErr error
+	for _, path := range paths {
+		conn, err := dialPipe(ctx, path)
+		if err != nil {
+			log.Debugf("dial daemon pipe %s: %v", path, err)
+			lastErr = err
+			continue
+		}
+
+		// A pipe in the protected namespace could only have been created by an
+		// administrator or LocalSystem, so its name is the guarantee. Any other
+		// name has to be checked, because any local user can create one.
+		if !IsProtectedPipePath(path) {
+			if err := ipcauth.PipeServerTrusted(conn); err != nil {
+				if closeErr := conn.Close(); closeErr != nil {
+					log.Debugf("close untrusted pipe %s: %v", path, closeErr)
+				}
+				lastErr = fmt.Errorf("%s: %w", path, err)
+				continue
+			}
+		}
+
+		return conn, nil
+	}
+
+	if lastErr == nil {
+		lastErr = errors.New("no daemon pipe to connect to")
+	}
+	return nil, lastErr
+}
+
+// dialPipe connects to the daemon control pipe at SECURITY_IDENTIFICATION.
+// winio's plain DialPipe connects at SECURITY_ANONYMOUS, under which the daemon
+// cannot read the caller's token at all. Identification lets the daemon read the
+// caller's SID and groups without granting it the ability to act as the caller.
+func dialPipe(ctx context.Context, path string) (net.Conn, error) {
+	access := uint32(windows.GENERIC_READ | windows.GENERIC_WRITE)
+	return winio.DialPipeAccessImpLevel(ctx, path, access, winio.PipeImpLevelIdentification)
+}

client/internal/daemonaddr/resolve_pipe_other.go

@@ -0,0 +1,9 @@
+//go:build !windows
+
+package daemonaddr
+
+// ResolveDaemonAddr is a no-op off Windows, where there is no named-pipe
+// default to fall back from.
+func ResolveDaemonAddr(addr string) string {
+	return addr
+}

client/internal/daemonaddr/resolve_pipe_windows.go

@@ -0,0 +1,82 @@
+//go:build windows
+
+package daemonaddr
+
+import (
+	"net"
+	"strings"
+	"time"
+
+	"github.com/Microsoft/go-winio"
+	log "github.com/sirupsen/logrus"
+)
+
+// probeTimeout bounds each transport probe. Both are local, so a daemon that is
+// listening answers immediately and one that is not fails immediately.
+const probeTimeout = 300 * time.Millisecond
+
+// ResolveDaemonAddr keeps a client on the named pipe and never silently moves it
+// off. When the pipe does not answer it checks the legacy loopback TCP address, so
+// a client meeting a daemon that has not restarted since the upgrade can say what
+// is wrong, but it does not connect there.
+//
+// Using that address automatically would be a downgrade the user never asked for:
+// any local process can bind 127.0.0.1 while the daemon is not listening, and the
+// transport carries no caller identity, so a client that accepted whatever answered
+// would hand a setup key, a pre-shared key or an SSO prompt to a local impostor. An
+// operator who needs the legacy address during the upgrade window can still pass
+// --daemon-addr explicitly, which is a deliberate choice and still refuses the
+// privileged operations.
+//
+// Only the pipe address is resolved. A custom address is left alone, though passing
+// --daemon-addr npipe://netbird explicitly is indistinguishable from the default
+// here, so it is treated the same way.
+func ResolveDaemonAddr(addr string) string {
+	if addr != WindowsPipeAddr {
+		return addr
+	}
+
+	for _, path := range PipePaths("netbird") {
+		if pipeAvailable(path) {
+			return addr
+		}
+	}
+
+	if tcpAvailable(legacyWindowsAddr) {
+		log.Warnf("the daemon is not serving %s, but something is listening on the legacy %s. "+
+			"Restart the NetBird service so it serves the pipe. That address is not used automatically: "+
+			"any local user can bind it and it carries no caller identity, so pass --daemon-addr %s "+
+			"explicitly if you accept that",
+			WindowsPipeAddr, legacyWindowsAddr, legacyWindowsAddr)
+	}
+
+	return addr
+}
+
+func pipeAvailable(path string) bool {
+	timeout := probeTimeout
+	conn, err := winio.DialPipe(path, &timeout)
+	if err != nil {
+		return false
+	}
+	if err := conn.Close(); err != nil {
+		log.Debugf("close daemon pipe probe: %v", err)
+	}
+	return true
+}
+
+func tcpAvailable(addr string) bool {
+	host := addr
+	if _, after, ok := strings.Cut(addr, "://"); ok {
+		host = after
+	}
+
+	conn, err := net.DialTimeout("tcp", host, probeTimeout)
+	if err != nil {
+		return false
+	}
+	if err := conn.Close(); err != nil {
+		log.Debugf("close daemon TCP probe: %v", err)
+	}
+	return true
+}

client/internal/ipcauth/creds_stub.go

@@ -0,0 +1,31 @@
+//go:build !linux && !darwin && !freebsd && !windows
+
+package ipcauth
+
+import (
+	"errors"
+	"net"
+
+	"google.golang.org/grpc/credentials"
+)
+
+// errUnsupported is returned on platforms with no local peer-identity
+// primitive, so consumers fail closed instead of guessing an identity.
+var errUnsupported = errors.New("peer identity is not available on this platform")
+
+// NewTransportCredentials returns nil: without a peer-identity primitive the
+// daemon cannot authenticate local callers, and the caller must treat that as
+// "authorization cannot be enforced".
+func NewTransportCredentials() credentials.TransportCredentials {
+	return nil
+}
+
+// PeerIdentity always fails on this platform.
+func PeerIdentity(net.Conn) (Identity, error) {
+	return Identity{}, errUnsupported
+}
+
+// ConnIdentity always fails on this platform.
+func ConnIdentity(net.Conn) (Identity, error) {
+	return Identity{}, errUnsupported
+}

client/internal/ipcauth/creds_unix.go

@@ -0,0 +1,56 @@
+//go:build linux || darwin || freebsd
+
+package ipcauth
+
+import (
+	"context"
+	"net"
+
+	"google.golang.org/grpc/credentials"
+)
+
+// NewTransportCredentials returns gRPC transport credentials that expose the
+// caller's kernel-authenticated identity via IdentityFromContext. It returns
+// nil on platforms that have no peer-identity primitive, which the caller must
+// treat as "authorization cannot be enforced".
+//
+// The handshake exchanges no bytes on the wire, so a client dialing with
+// insecure credentials interoperates with a server using these. That keeps
+// older CLI and UI binaries working against an upgraded daemon.
+func NewTransportCredentials() credentials.TransportCredentials {
+	return unixCreds{}
+}
+
+// ConnIdentity extracts the caller's identity from an accepted local IPC
+// connection. It is shared by the gRPC transport credentials and by the JSON
+// gateway, which reads the identity of its own HTTP clients.
+func ConnIdentity(conn net.Conn) (Identity, error) {
+	return PeerIdentity(conn)
+}
+
+type unixCreds struct{}
+
+func (unixCreds) ClientHandshake(_ context.Context, _ string, conn net.Conn) (net.Conn, credentials.AuthInfo, error) {
+	return conn, AuthInfo{}, nil
+}
+
+// ServerHandshake extracts the peer identity and fails closed when it cannot
+// be read, so a connection whose caller is unknown never reaches a handler.
+func (unixCreds) ServerHandshake(conn net.Conn) (net.Conn, credentials.AuthInfo, error) {
+	id, err := ConnIdentity(conn)
+	if err != nil {
+		return nil, nil, err
+	}
+	return conn, AuthInfo{
+		CommonAuthInfo: credentials.CommonAuthInfo{SecurityLevel: credentials.NoSecurity},
+		Identity:       id,
+	}, nil
+}
+
+func (unixCreds) Info() credentials.ProtocolInfo {
+	return credentials.ProtocolInfo{SecurityProtocol: AuthInfo{}.AuthType()}
+}
+
+func (unixCreds) Clone() credentials.TransportCredentials { return unixCreds{} }
+
+func (unixCreds) OverrideServerName(string) error { return nil }

client/internal/ipcauth/creds_windows.go

@@ -0,0 +1,194 @@
+//go:build windows
+
+package ipcauth
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"runtime"
+
+	log "github.com/sirupsen/logrus"
+	"golang.org/x/sys/windows"
+	"google.golang.org/grpc/credentials"
+)
+
+var (
+	modadvapi32                    = windows.NewLazySystemDLL("advapi32.dll")
+	procImpersonateNamedPipeClient = modadvapi32.NewProc("ImpersonateNamedPipeClient")
+)
+
+// DefaultPipeSDDL is the security descriptor for the daemon control pipe.
+//
+//	D:P          protected DACL, no inheritance
+//	(A;;GA;;;SY) allow GENERIC_ALL to LocalSystem (the daemon's service account)
+//	(A;;GA;;;WD) allow GENERIC_ALL to Everyone
+//
+// Any local caller may connect, as with a Unix socket at 0666; what a caller may
+// actually do is decided from its token, not from the DACL. Remote callers are not
+// a concern here: winio.ListenPipe creates the pipe with
+// FILE_PIPE_REJECT_REMOTE_CLIENTS, so NPFS rejects connections from other machines
+// before the descriptor is consulted.
+//
+// A deny ACE on the NETWORK SID would not add anything and would break callers:
+// that SID is present in any network-logon token, which includes OpenSSH and WinRM
+// sessions, so it denies administrators driving the CLI over SSH and denies the
+// daemon itself when started from such a session.
+func DefaultPipeSDDL() string {
+	return "D:P(A;;GA;;;SY)(A;;GA;;;WD)"
+}
+
+// NewTransportCredentials returns gRPC transport credentials that derive the
+// caller's identity from the named-pipe client token.
+//
+// The client must connect at SECURITY_IDENTIFICATION for the daemon to be able
+// to read its token, which is what DialNamedPipe does.
+func NewTransportCredentials() credentials.TransportCredentials {
+	return winpipeCreds{}
+}
+
+// ConnIdentity extracts the caller's identity from an accepted named-pipe
+// connection by impersonating the pipe client and reading its token. It is
+// shared by the gRPC transport credentials and by the JSON gateway, which
+// reads the identity of its own HTTP clients.
+func ConnIdentity(conn net.Conn) (Identity, error) {
+	// go-winio's pipe connection embeds *win32File, which exposes Fd().
+	fdConn, ok := conn.(interface{ Fd() uintptr })
+	if !ok {
+		return Identity{}, fmt.Errorf("connection %T does not expose a pipe handle", conn)
+	}
+	return pipeClientIdentity(windows.Handle(fdConn.Fd()))
+}
+
+type winpipeCreds struct{}
+
+func (winpipeCreds) ClientHandshake(_ context.Context, _ string, conn net.Conn) (net.Conn, credentials.AuthInfo, error) {
+	return conn, AuthInfo{}, nil
+}
+
+// ServerHandshake extracts the connecting client's identity and fails closed
+// when the handle or token cannot be read, so a connection whose caller is
+// unknown never reaches a handler.
+func (winpipeCreds) ServerHandshake(conn net.Conn) (net.Conn, credentials.AuthInfo, error) {
+	id, err := ConnIdentity(conn)
+	if err != nil {
+		return nil, nil, err
+	}
+	return conn, AuthInfo{
+		CommonAuthInfo: credentials.CommonAuthInfo{SecurityLevel: credentials.NoSecurity},
+		Identity:       id,
+	}, nil
+}
+
+func (winpipeCreds) Info() credentials.ProtocolInfo {
+	return credentials.ProtocolInfo{SecurityProtocol: AuthInfo{}.AuthType()}
+}
+
+func (winpipeCreds) Clone() credentials.TransportCredentials { return winpipeCreds{} }
+
+func (winpipeCreds) OverrideServerName(string) error { return nil }
+
+// pipeClientIdentity reads the connecting client's user SID, usable group
+// SIDs, and elevation state by impersonating the pipe client on this thread
+// and reading the resulting impersonation token.
+func pipeClientIdentity(handle windows.Handle) (id Identity, err error) {
+	// Impersonation is per-thread, so the goroutine must stay on this thread
+	// until RevertToSelf, otherwise an unrelated goroutine could inherit the
+	// impersonated context.
+	runtime.LockOSThread()
+
+	// The thread only goes back to the runtime's pool once it is provably no
+	// longer impersonating the client. If the revert fails, leaving it locked
+	// makes Go terminate it when this goroutine exits, which costs one thread
+	// and keeps a thread running as the client from ever being reused.
+	clean := false
+	defer func() {
+		if clean {
+			runtime.UnlockOSThread()
+		}
+	}()
+
+	if err = impersonateNamedPipeClient(handle); err != nil {
+		clean = true
+		return Identity{}, fmt.Errorf("impersonate named pipe client: %w", err)
+	}
+	defer func() {
+		// Surface the revert failure only when nothing else failed: leaving
+		// the thread impersonated is worse than the original error.
+		revErr := windows.RevertToSelf()
+		if revErr != nil {
+			if err == nil {
+				err = fmt.Errorf("revert impersonation: %w", revErr)
+			}
+			return
+		}
+		clean = true
+	}()
+
+	// openAsSelf=true opens the token with the daemon's own process context
+	// rather than the impersonated client's, so the open cannot fail because
+	// the client lacks access to its own token.
+	var token windows.Token
+	if err = windows.OpenThreadToken(windows.CurrentThread(), windows.TOKEN_QUERY, true, &token); err != nil {
+		return Identity{}, fmt.Errorf("open thread token: %w", err)
+	}
+	defer func() {
+		if cerr := token.Close(); cerr != nil {
+			log.Debugf("close client token: %v", cerr)
+		}
+	}()
+
+	return identityFromToken(token)
+}
+
+// identityFromToken reads the user SID, usable group SIDs and elevation state
+// out of a Windows token.
+func identityFromToken(token windows.Token) (Identity, error) {
+	user, err := token.GetTokenUser()
+	if err != nil {
+		return Identity{}, fmt.Errorf("read token user: %w", err)
+	}
+
+	groups, err := tokenGroupSIDs(token)
+	if err != nil {
+		return Identity{}, err
+	}
+
+	return Identity{
+		SID:      user.User.Sid.String(),
+		Groups:   groups,
+		Elevated: token.IsElevated(),
+	}, nil
+}
+
+// tokenGroupSIDs returns the SIDs of the groups the token can actually
+// exercise. Groups that are disabled or marked deny-only are skipped: a
+// UAC-filtered administrator carries BUILTIN\Administrators as deny-only, and
+// treating that as membership would hand every admin account privilege it
+// cannot currently use.
+func tokenGroupSIDs(token windows.Token) ([]string, error) {
+	tg, err := token.GetTokenGroups()
+	if err != nil {
+		return nil, fmt.Errorf("read token groups: %w", err)
+	}
+
+	var sids []string
+	for _, g := range tg.AllGroups() {
+		if g.Attributes&windows.SE_GROUP_ENABLED == 0 {
+			continue
+		}
+		if g.Attributes&windows.SE_GROUP_USE_FOR_DENY_ONLY != 0 {
+			continue
+		}
+		sids = append(sids, g.Sid.String())
+	}
+	return sids, nil
+}
+
+func impersonateNamedPipeClient(h windows.Handle) error {
+	r, _, e := procImpersonateNamedPipeClient.Call(uintptr(h))
+	if r == 0 {
+		return e
+	}
+	return nil
+}

client/internal/ipcauth/forward.go

@@ -0,0 +1,272 @@
+package ipcauth
+
+import (
+	"context"
+	"crypto/rand"
+	"crypto/subtle"
+	"encoding/hex"
+	"fmt"
+	"slices"
+	"strconv"
+	"strings"
+
+	"google.golang.org/grpc/metadata"
+)
+
+// Metadata keys the local JSON gateway uses to forward the identity of its own
+// HTTP client to the daemon. The gateway runs inside the daemon process and
+// re-dials the daemon over the control socket, so without forwarding every
+// JSON request would appear to come from the daemon itself.
+const (
+	// mdFwd marks a request as forwarded by the JSON gateway. It is always
+	// set, even when the gateway could not read its client's identity, so the
+	// daemon can tell "no identity available" apart from "not forwarded".
+	mdFwd         = "x-netbird-fwd"
+	mdFwdUID      = "x-netbird-fwd-uid"      // Unix user ID
+	mdFwdGID      = "x-netbird-fwd-gid"      // Unix primary group ID
+	mdFwdSID      = "x-netbird-fwd-sid"      // Windows user SID
+	mdFwdGroup    = "x-netbird-fwd-group"    // Windows group SID, repeated
+	mdFwdElevated = "x-netbird-fwd-elevated" // Windows, "1" when elevated
+
+	// mdFwdProof proves the forwarded identity was stamped by this process. The
+	// gateway runs inside the daemon, so a secret held in memory is available to
+	// the only legitimate producer and to nothing else.
+	mdFwdProof = "x-netbird-fwd-proof"
+)
+
+// forwardKeys is every metadata key the gateway sets. An HTTP client must never
+// be able to supply one itself: see IsReservedForwardKey.
+var forwardKeys = []string{mdFwd, mdFwdUID, mdFwdGID, mdFwdSID, mdFwdGroup, mdFwdElevated, mdFwdProof}
+
+// forwardProof authenticates the gateway's forwarding metadata. It is generated
+// once per daemon process and never leaves it: it is not written to disk, not
+// logged, and not sent anywhere except over the daemon's own control socket to
+// itself.
+//
+// Without it, trusting a forwarded identity rests on every layer in front of it
+// stripping incoming forwarding keys, and on each key's value shape being
+// distinguishable from an injected one. A single injected group SID or an
+// injected "elevated" flag has the same shape as a legitimate one, so no
+// cardinality rule can catch it. Requiring the proof means metadata that did not
+// come from this process is refused whatever it contains.
+var forwardProof = mustForwardProof()
+
+func mustForwardProof() string {
+	var buf [32]byte
+	if _, err := rand.Read(buf[:]); err != nil {
+		// Continuing would leave the forwarded path authenticated by a
+		// predictable value, which is worse than not starting.
+		panic(fmt.Sprintf("generate identity forwarding proof: %v", err))
+	}
+	return hex.EncodeToString(buf[:])
+}
+
+// IsReservedForwardKey reports whether a gRPC metadata key belongs to the
+// gateway's identity forwarding, and therefore must be dropped when it arrives
+// from outside.
+//
+// grpc-gateway maps "Grpc-Metadata-<key>" request headers into gRPC metadata and
+// joins them ahead of the values its own annotators add. Without dropping these,
+// an HTTP client could hand the daemon "x-netbird-fwd-uid: 0" and be believed,
+// because the daemon trusts forwarded metadata when the transport peer is the
+// (privileged) gateway.
+func IsReservedForwardKey(key string) bool {
+	key = strings.ToLower(key)
+	return slices.Contains(forwardKeys, key)
+}
+
+// ForwardIdentityMetadata encodes an HTTP client's identity for the JSON
+// gateway to forward to the daemon. When known is false only the marker is
+// set, which makes the daemon treat the caller as unidentified rather than as
+// the daemon itself.
+func ForwardIdentityMetadata(id Identity, known bool) metadata.MD {
+	md := metadata.MD{}
+	md.Set(mdFwd, "1")
+	md.Set(mdFwdProof, forwardProof)
+	if !known {
+		return md
+	}
+
+	if id.IsWindows() {
+		md.Set(mdFwdSID, id.SID)
+		if len(id.Groups) > 0 {
+			md.Set(mdFwdGroup, id.Groups...)
+		}
+		if id.Elevated {
+			md.Set(mdFwdElevated, "1")
+		}
+		return md
+	}
+
+	md.Set(mdFwdUID, strconv.FormatUint(uint64(id.UID), 10))
+	md.Set(mdFwdGID, strconv.FormatUint(uint64(id.GID), 10))
+	return md
+}
+
+// CallerIdentity returns the identity to authorize a request against. For a
+// direct connection that is the transport peer's kernel identity. For a
+// request relayed by the local JSON gateway it is the identity the gateway
+// forwarded, since the transport peer is then the daemon itself.
+//
+// A forwarded identity is only honoured when the transport peer is the daemon's
+// own identity and the metadata carries this process's forwarding proof, so
+// forged forwarding metadata gains a caller nothing. A forwarded request that
+// carries no identity is reported as unidentified, never as the daemon.
+//
+// The second return value is false when no identity could be established, and
+// callers MUST fail closed in that case.
+func CallerIdentity(ctx context.Context) (Identity, bool) {
+	id, ok := IdentityFromContext(ctx)
+	if !ok {
+		return Identity{}, false
+	}
+
+	// A forwarding key that arrives more than once did not come from the gateway
+	// alone, so nothing about the request can be trusted to describe its caller.
+	// Refusing outright matters because the alternative reading, "not forwarded",
+	// would authorize the request as the transport peer, which on the gateway's
+	// connection is the daemon itself.
+	if duplicatedForwardKey(ctx) {
+		return Identity{}, false
+	}
+
+	forwarded := isForwarded(ctx)
+
+	// Our own process on the other end of the socket is the JSON gateway, the only
+	// thing that dials the daemon from inside it. Such a call must carry a
+	// forwarded identity; without one there is no caller to authorize, and
+	// treating it as the daemon would authorize whatever reached the JSON socket.
+	// Only Linux reports the peer PID, so this is a belt on top of the gateway's
+	// interceptor rather than the sole guarantee.
+	if id.PID != 0 && int(id.PID) == selfPID && !forwarded {
+		return Identity{}, false
+	}
+
+	// Only the gateway's own connection may speak for someone else. Being
+	// privileged is not enough and not the point: the gateway runs inside the
+	// daemon, so it dials as the daemon's identity whatever user that is, which
+	// also covers a rootless container.
+	if !forwarded || !IsDaemonSelf(id) {
+		return id, true
+	}
+
+	// Speaking for someone else additionally requires the proof only this process
+	// holds. Refusing is the only safe reading: the transport peer here is the
+	// daemon itself, so falling back to it would authorize the request as the
+	// daemon. This is also what makes the forwarded values trustworthy once
+	// accepted, so they need no shape checks of their own.
+	if !authenticForward(ctx) {
+		return Identity{}, false
+	}
+
+	return forwardedIdentity(ctx)
+}
+
+// duplicatedForwardKey reports whether any forwarding key carries more than one
+// value. The gateway's interceptor sets each key exactly once and replaces what
+// was already there, so a repeat means a second source supplied it.
+func duplicatedForwardKey(ctx context.Context) bool {
+	md, ok := metadata.FromIncomingContext(ctx)
+	if !ok {
+		return false
+	}
+	for _, key := range forwardKeys {
+		// Group SIDs are legitimately repeated; the rest identify the caller.
+		if key == mdFwdGroup {
+			continue
+		}
+		if len(md.Get(key)) > 1 {
+			return true
+		}
+	}
+	return false
+}
+
+// authenticForward reports whether the request carries this process's forwarding
+// proof, which only the in-process JSON gateway can supply.
+func authenticForward(ctx context.Context) bool {
+	md, ok := metadata.FromIncomingContext(ctx)
+	if !ok {
+		return false
+	}
+	got := mdSingle(md, mdFwdProof)
+	return subtle.ConstantTimeCompare([]byte(got), []byte(forwardProof)) == 1
+}
+
+// isForwarded reports whether the request carries the JSON gateway marker.
+func isForwarded(ctx context.Context) bool {
+	md, ok := metadata.FromIncomingContext(ctx)
+	if !ok {
+		return false
+	}
+	return mdSingle(md, mdFwd) != ""
+}
+
+// forwardedIdentity decodes the identity the JSON gateway attached.
+func forwardedIdentity(ctx context.Context) (Identity, bool) {
+	md, ok := metadata.FromIncomingContext(ctx)
+	if !ok {
+		return Identity{}, false
+	}
+
+	if sid := mdSingle(md, mdFwdSID); sid != "" {
+		return Identity{
+			SID: sid,
+			// Repeated by design, one value per group, and only reachable once
+			// the forwarding proof has been verified.
+			Groups:   md.Get(mdFwdGroup),
+			Elevated: mdSingle(md, mdFwdElevated) == "1",
+		}, true
+	}
+
+	uid, err := strconv.ParseUint(mdSingle(md, mdFwdUID), 10, 32)
+	if err != nil {
+		return Identity{}, false
+	}
+
+	id := Identity{UID: uint32(uid)}
+	if gid, err := strconv.ParseUint(mdSingle(md, mdFwdGID), 10, 32); err == nil {
+		id.GID = uint32(gid)
+	}
+	return id, true
+}
+
+// mdSingle returns the value of a forwarded key only when exactly one was
+// supplied. The gateway's interceptor sets each key exactly once, so more than one
+// value means something else also supplied it, and the whole identity is treated as
+// unknown rather than picking a winner. Defence in depth behind the gateway's
+// header filter.
+func mdSingle(md metadata.MD, key string) string {
+	if v := md.Get(key); len(v) == 1 {
+		return v[0]
+	}
+	return ""
+}
+
+// WithForwardedIdentity stamps id onto a context's outgoing metadata for the JSON
+// gateway's call to the daemon, replacing any forwarding keys already present so
+// values supplied from outside cannot survive alongside it.
+//
+// This is deliberately not done with runtime.WithMetadata: grpc-gateway skips its
+// annotators entirely when no request header maps to metadata ("if len(pairs) == 0
+// { return ctx, nil, nil }", runtime/context.go), which an HTTP/1.0 request with no
+// Host header over a unix socket achieves. The daemon would then see an unmarked
+// call whose transport peer is the daemon's own identity, and authorize it as the
+// daemon. A client interceptor runs for every RPC regardless of headers.
+func WithForwardedIdentity(ctx context.Context, id Identity, known bool) context.Context {
+	md, ok := metadata.FromOutgoingContext(ctx)
+	if !ok {
+		md = metadata.MD{}
+	} else {
+		md = md.Copy()
+	}
+
+	for _, key := range forwardKeys {
+		delete(md, key)
+	}
+	for key, values := range ForwardIdentityMetadata(id, known) {
+		md[key] = values
+	}
+
+	return metadata.NewOutgoingContext(ctx, md)
+}

client/internal/ipcauth/forward_test.go

@@ -0,0 +1,214 @@
+package ipcauth
+
+import (
+	"context"
+	"testing"
+
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/peer"
+)
+
+// transportCtx builds a request context as the daemon's transport credentials
+// would: the identity of whoever opened the socket, plus whatever metadata the
+// request carried.
+func transportCtx(id Identity, md metadata.MD) context.Context {
+	ctx := peer.NewContext(context.Background(), &peer.Peer{
+		AuthInfo: AuthInfo{
+			CommonAuthInfo: credentials.CommonAuthInfo{SecurityLevel: credentials.NoSecurity},
+			Identity:       id,
+		},
+	})
+	if md != nil {
+		ctx = metadata.NewIncomingContext(ctx, md)
+	}
+	return ctx
+}
+
+var (
+	root       = Identity{UID: 0}
+	unprivUser = Identity{UID: 1000, GID: 1000}
+)
+
+// asDaemon pins which identity counts as this process for the duration of a test.
+// Without it the test binary's own uid decides, which silently changes what
+// "the gateway" means.
+func asDaemon(t *testing.T, id Identity) {
+	t.Helper()
+	prevID, prevKnown, prevDelegate := selfIdentity, selfKnown, selfMayDelegate
+	t.Cleanup(func() { selfIdentity, selfKnown, selfMayDelegate = prevID, prevKnown, prevDelegate })
+	selfIdentity, selfKnown = id, true
+	selfMayDelegate = !id.IsPrivileged()
+}
+
+func TestCallerIdentity_DirectConnections(t *testing.T) {
+	t.Run("no transport credentials is not an identity", func(t *testing.T) {
+		if _, ok := CallerIdentity(context.Background()); ok {
+			t.Fatal("a caller with no credentials must not be identified")
+		}
+	})
+
+	t.Run("a direct caller is its transport identity", func(t *testing.T) {
+		id, ok := CallerIdentity(transportCtx(unprivUser, nil))
+		if !ok || id.UID != 1000 {
+			t.Fatalf("got %v ok=%t, want uid 1000", id, ok)
+		}
+	})
+
+	// The whole point of honouring forwarded metadata only from a privileged
+	// transport peer: an unprivileged caller can set any metadata it likes on its
+	// own connection to the daemon socket.
+	t.Run("an unprivileged caller cannot forge an identity", func(t *testing.T) {
+		asDaemon(t, root)
+		forged := metadata.Pairs(mdFwd, "1", mdFwdUID, "0", mdFwdGID, "0")
+		id, ok := CallerIdentity(transportCtx(unprivUser, forged))
+		if !ok {
+			t.Fatal("caller should still be identified, as itself")
+		}
+		if id.IsPrivileged() || id.UID != 1000 {
+			t.Fatalf("forged metadata was believed: got %v", id)
+		}
+	})
+}
+
+func TestCallerIdentity_GatewayForwarding(t *testing.T) {
+	t.Run("the gateway's client identity is used, not the gateway's own", func(t *testing.T) {
+		asDaemon(t, root)
+		md := ForwardIdentityMetadata(unprivUser, true)
+		id, ok := CallerIdentity(transportCtx(root, md))
+		if !ok {
+			t.Fatal("forwarded identity should be usable")
+		}
+		if id.IsPrivileged() || id.UID != 1000 {
+			t.Fatalf("got %v, want the forwarded uid 1000 and not privileged", id)
+		}
+	})
+
+	t.Run("a privileged gateway client stays privileged", func(t *testing.T) {
+		asDaemon(t, root)
+		md := ForwardIdentityMetadata(root, true)
+		id, ok := CallerIdentity(transportCtx(root, md))
+		if !ok || !id.IsPrivileged() {
+			t.Fatalf("got %v ok=%t, want a privileged identity", id, ok)
+		}
+	})
+
+	// A JSON socket the gateway cannot read peer credentials from (a TCP socket,
+	// say) must not make every request look like the daemon itself.
+	t.Run("an unreadable client identity is unknown, not the daemon", func(t *testing.T) {
+		asDaemon(t, root)
+		md := ForwardIdentityMetadata(Identity{}, false)
+		if _, ok := CallerIdentity(transportCtx(root, md)); ok {
+			t.Fatal("a forwarded request with no identity must not be identified")
+		}
+	})
+
+	// grpc-gateway turns Grpc-Metadata-<key> headers into gRPC metadata and joins
+	// them ahead of its annotators' values. If an HTTP client's header survived
+	// that, this is the shape the daemon would see: the attacker's uid 0 first,
+	// the real uid second. The gateway filters those headers out, and reading a
+	// duplicated key as unknown makes the daemon safe even if it did not.
+	t.Run("a duplicated key from an injected header is not believed", func(t *testing.T) {
+		asDaemon(t, root)
+		md := metadata.MD{}
+		md.Append(mdFwd, "1")
+		md.Append(mdFwdUID, "0")    // injected by the HTTP client
+		md.Append(mdFwdUID, "1000") // appended by the gateway's annotator
+		if id, ok := CallerIdentity(transportCtx(root, md)); ok {
+			t.Fatalf("injected uid was accepted: got %v", id)
+		}
+	})
+
+	t.Run("a duplicated marker is not believed either", func(t *testing.T) {
+		asDaemon(t, root)
+		md := metadata.MD{}
+		md.Append(mdFwd, "1")
+		md.Append(mdFwd, "1")
+		md.Append(mdFwdUID, "1000")
+		// A repeated marker must not be read as "not forwarded": that would
+		// authorize the request as the transport peer, which on the gateway's
+		// connection is the daemon itself.
+		if id, ok := CallerIdentity(transportCtx(root, md)); ok {
+			t.Fatalf("a duplicated marker was believed: got %v", id)
+		}
+	})
+
+	// The layers in front of this (the gateway's header matcher, and its
+	// interceptor replacing every forwarding key) are what keep outside metadata
+	// from arriving at all. The proof is what the daemon can check for itself, and
+	// it is the only defence that works for a value whose legitimate shape is
+	// indistinguishable from an injected one: a lone group SID, or "elevated".
+	t.Run("forwarding metadata without this process's proof is refused", func(t *testing.T) {
+		asDaemon(t, root)
+		for name, md := range map[string]metadata.MD{
+			"no proof":    metadata.Pairs(mdFwd, "1", mdFwdUID, "0"),
+			"wrong proof": metadata.Pairs(mdFwd, "1", mdFwdUID, "0", mdFwdProof, "deadbeef"),
+			"windows identity without a proof": metadata.Pairs(mdFwd, "1",
+				mdFwdSID, "S-1-5-21-1-2-3-1001", mdFwdGroup, sidAdministrators, mdFwdElevated, "1"),
+		} {
+			t.Run(name, func(t *testing.T) {
+				if id, ok := CallerIdentity(transportCtx(root, md)); ok {
+					t.Fatalf("unstamped forwarding metadata was believed: got %v", id)
+				}
+			})
+		}
+	})
+
+	// A caller that reaches the gateway cannot see the proof, so it cannot append
+	// a group of its own to a genuine forwarded identity: doing so would have to
+	// go through the interceptor, which replaces the whole set.
+	t.Run("a group appended to a stamped identity does not survive the interceptor", func(t *testing.T) {
+		asDaemon(t, root)
+		injected := metadata.MD{}
+		injected.Append(mdFwdGroup, sidAdministrators)
+
+		ctx := WithForwardedIdentity(metadata.NewOutgoingContext(context.Background(), injected),
+			Identity{SID: "S-1-5-21-1-2-3-1001"}, true)
+		out, ok := metadata.FromOutgoingContext(ctx)
+		if !ok {
+			t.Fatal("no outgoing metadata")
+		}
+		if groups := out.Get(mdFwdGroup); len(groups) != 0 {
+			t.Fatalf("injected group survived: %v", groups)
+		}
+	})
+}
+
+func TestIsReservedForwardKey(t *testing.T) {
+	for _, key := range forwardKeys {
+		if !IsReservedForwardKey(key) {
+			t.Errorf("%q must be reserved", key)
+		}
+	}
+
+	// grpc-gateway canonicalises header names, so the check has to be
+	// case-insensitive.
+	if !IsReservedForwardKey("X-Netbird-Fwd-Uid") {
+		t.Error("the check must be case-insensitive")
+	}
+
+	for _, key := range []string{"authorization", "x-netbird", "x-netbird-fwd-uid-extra", ""} {
+		if IsReservedForwardKey(key) {
+			t.Errorf("%q must not be reserved", key)
+		}
+	}
+}
+
+func TestForwardIdentityMetadata_AlwaysMarksForwarded(t *testing.T) {
+	for _, tc := range []struct {
+		name  string
+		id    Identity
+		known bool
+	}{
+		{"known unix identity", unprivUser, true},
+		{"unknown identity", Identity{}, false},
+		{"windows identity", Identity{SID: "S-1-5-21-1-2-3-1001", Elevated: true}, true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			md := ForwardIdentityMetadata(tc.id, tc.known)
+			if got := md.Get(mdFwd); len(got) != 1 || got[0] != "1" {
+				t.Fatalf("marker = %v, want exactly one \"1\"", got)
+			}
+		})
+	}
+}

client/internal/ipcauth/identity.go

@@ -0,0 +1,127 @@
+// Package ipcauth provides the kernel-authenticated identity of a local IPC
+// (gRPC) caller and the transport credentials that surface it into the gRPC
+// context, so the daemon can authorize individual RPCs by caller identity.
+//
+// On Unix the identity is read from the kernel via SO_PEERCRED (Linux) or
+// LOCAL_PEERCRED (Darwin/FreeBSD). On Windows it is derived from the
+// named-pipe client token. Platforms without a peer-identity primitive get no
+// credentials, and every consumer must fail closed when no identity is
+// available.
+package ipcauth
+
+import (
+	"context"
+	"fmt"
+	"slices"
+
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/peer"
+)
+
+// Well-known Windows SIDs that identify a fully privileged principal.
+const (
+	sidLocalSystem    = "S-1-5-18"     // NT AUTHORITY\SYSTEM
+	sidLocalService   = "S-1-5-19"     // NT AUTHORITY\LOCAL SERVICE
+	sidNetworkService = "S-1-5-20"     // NT AUTHORITY\NETWORK SERVICE
+	sidAdministrators = "S-1-5-32-544" // BUILTIN\Administrators
+)
+
+// Identity is the kernel-authenticated identity of a local IPC caller. The
+// zero value is not a valid identity: consumers must only use one obtained
+// with a true ok/nil error return.
+type Identity struct {
+	// UID and GID are the caller's Unix user ID and primary group ID. Both are
+	// zero on Windows, where SID is authoritative instead.
+	UID uint32
+	GID uint32
+
+	// SID is the caller's Windows security identifier, empty on Unix.
+	SID string
+
+	// Groups holds the caller's Windows group SIDs, captured from the client
+	// token at handshake time. Only groups that are enabled and not
+	// deny-only are captured, so a group listed here is one the caller can
+	// actually exercise. Empty on Unix.
+	Groups []string
+
+	// Elevated reports whether the Windows client token is elevated (running
+	// as administrator, or an administrator with UAC turned off). Always false
+	// on Unix, where privilege is uid 0.
+	Elevated bool
+
+	// PID is the caller's process ID where the platform reports it (Linux's
+	// SO_PEERCRED), and 0 where it does not. It identifies the daemon's own
+	// process dialling itself, which is what the JSON gateway does, and is never
+	// used to grant anything.
+	PID int32
+}
+
+// IsWindows reports whether this identity is a Windows principal (SID-based)
+// rather than a Unix uid/gid principal.
+func (i Identity) IsWindows() bool {
+	return i.SID != ""
+}
+
+// IsPrivileged reports whether the caller is the platform's administrative
+// principal, which is what the daemon requires for changes that cross the
+// user-to-root boundary.
+//
+// On Windows the decision comes from the caller's token rather than from
+// account names or group RIDs: an elevated token, one of the service accounts
+// the daemon itself may run as, or a token with BUILTIN\Administrators
+// enabled. A UAC-filtered administrator has that group marked deny-only, and
+// deny-only groups are dropped when the identity is captured, so such a
+// caller is correctly reported as unprivileged. Domain group memberships
+// (Domain Admins and friends) are deliberately not consulted: they say
+// nothing about what this token may do on this machine.
+func (i Identity) IsPrivileged() bool {
+	if !i.IsWindows() {
+		return i.UID == 0
+	}
+
+	if i.Elevated {
+		return true
+	}
+
+	switch i.SID {
+	case sidLocalSystem, sidLocalService, sidNetworkService:
+		return true
+	}
+
+	return slices.Contains(i.Groups, sidAdministrators)
+}
+
+// String renders the identity for audit logs and denial messages.
+func (i Identity) String() string {
+	if i.IsWindows() {
+		return fmt.Sprintf("sid=%s elevated=%t", i.SID, i.Elevated)
+	}
+	return fmt.Sprintf("uid=%d gid=%d", i.UID, i.GID)
+}
+
+// AuthInfo carries the peer Identity as a gRPC credentials.AuthInfo so
+// handlers can retrieve it from the request context via IdentityFromContext.
+type AuthInfo struct {
+	credentials.CommonAuthInfo
+	Identity Identity
+}
+
+// AuthType identifies the authentication scheme.
+func (AuthInfo) AuthType() string { return "netbird-ipc-peercred" }
+
+// IdentityFromContext extracts the caller's kernel-authenticated identity from
+// the gRPC peer context. The second return value is false when no IPC
+// transport credentials were negotiated, which happens on a TCP daemon socket
+// and on platforms without a peer-identity primitive. Callers MUST fail closed
+// in that case.
+func IdentityFromContext(ctx context.Context) (Identity, bool) {
+	p, ok := peer.FromContext(ctx)
+	if !ok {
+		return Identity{}, false
+	}
+	info, ok := p.AuthInfo.(AuthInfo)
+	if !ok {
+		return Identity{}, false
+	}
+	return info.Identity, true
+}

client/internal/ipcauth/peercred_bsd.go

@@ -0,0 +1,43 @@
+//go:build darwin || freebsd
+
+package ipcauth
+
+import (
+	"fmt"
+	"net"
+
+	"golang.org/x/sys/unix"
+)
+
+// PeerIdentity reads the kernel-authenticated identity of the process on the
+// other end of a Unix socket via LOCAL_PEERCRED. The xucred is recorded by the
+// kernel at connect() time and carries the peer's uid and its group list, of
+// which the first entry is the primary group.
+func PeerIdentity(conn net.Conn) (Identity, error) {
+	uc, ok := conn.(*net.UnixConn)
+	if !ok {
+		return Identity{}, fmt.Errorf("connection is not a unix socket: %T", conn)
+	}
+
+	raw, err := uc.SyscallConn()
+	if err != nil {
+		return Identity{}, fmt.Errorf("raw conn: %w", err)
+	}
+
+	var cred *unix.Xucred
+	var credErr error
+	if err := raw.Control(func(fd uintptr) {
+		cred, credErr = unix.GetsockoptXucred(int(fd), unix.SOL_LOCAL, unix.LOCAL_PEERCRED)
+	}); err != nil {
+		return Identity{}, fmt.Errorf("control raw conn: %w", err)
+	}
+	if credErr != nil {
+		return Identity{}, fmt.Errorf("read LOCAL_PEERCRED: %w", credErr)
+	}
+
+	id := Identity{UID: cred.Uid}
+	if cred.Ngroups > 0 {
+		id.GID = cred.Groups[0]
+	}
+	return id, nil
+}

client/internal/ipcauth/peercred_linux.go

@@ -0,0 +1,39 @@
+//go:build linux
+
+package ipcauth
+
+import (
+	"fmt"
+	"net"
+
+	"golang.org/x/sys/unix"
+)
+
+// PeerIdentity reads the kernel-authenticated identity of the process on the
+// other end of a Unix socket via SO_PEERCRED. The credentials are recorded by
+// the kernel at connect() time and cannot be changed for the life of the
+// connection, so they are not spoofable by the caller.
+func PeerIdentity(conn net.Conn) (Identity, error) {
+	uc, ok := conn.(*net.UnixConn)
+	if !ok {
+		return Identity{}, fmt.Errorf("connection is not a unix socket: %T", conn)
+	}
+
+	raw, err := uc.SyscallConn()
+	if err != nil {
+		return Identity{}, fmt.Errorf("raw conn: %w", err)
+	}
+
+	var cred *unix.Ucred
+	var credErr error
+	if err := raw.Control(func(fd uintptr) {
+		cred, credErr = unix.GetsockoptUcred(int(fd), unix.SOL_SOCKET, unix.SO_PEERCRED)
+	}); err != nil {
+		return Identity{}, fmt.Errorf("control raw conn: %w", err)
+	}
+	if credErr != nil {
+		return Identity{}, fmt.Errorf("read SO_PEERCRED: %w", credErr)
+	}
+
+	return Identity{UID: cred.Uid, GID: cred.Gid, PID: cred.Pid}, nil
+}

client/internal/ipcauth/pipeserver_windows.go

@@ -0,0 +1,87 @@
+//go:build windows
+
+package ipcauth
+
+import (
+	"fmt"
+	"net"
+
+	log "github.com/sirupsen/logrus"
+	"golang.org/x/sys/windows"
+)
+
+// PipeServerTrusted reports an error unless the pipe behind conn was created by a
+// principal this client may hand secrets to. Clients call it for a pipe whose name
+// carries no guarantee of its own, which is any name outside the
+// ProtectedPrefix\Administrators namespace: that namespace already restricts
+// creation to administrators and LocalSystem, while a plain name can be created by
+// any local user before the daemon gets there.
+//
+// The decision is made from the pipe object's owner, not from the serving process,
+// because a client cannot open a process running as another user at all, and the
+// legitimate case is precisely an unprivileged client talking to a privileged
+// daemon. Trusted owners are the service accounts, BUILTIN\Administrators, and
+// this client's own user, the last of which is the daemon a user runs themselves
+// as in netstack mode. A pipe owned by anyone else gets no setup key, pre-shared
+// key or SSO prompt out of this client.
+func PipeServerTrusted(conn net.Conn) error {
+	// go-winio's pipe connection embeds *win32File, which exposes Fd().
+	fdConn, ok := conn.(interface{ Fd() uintptr })
+	if !ok {
+		return fmt.Errorf("connection %T does not expose a pipe handle", conn)
+	}
+
+	owner, err := pipeOwnerSID(windows.Handle(fdConn.Fd()))
+	if err != nil {
+		return err
+	}
+
+	if !trustedPipeOwner(owner) {
+		return fmt.Errorf("pipe owned by %s, which is neither an administrator nor this user", owner)
+	}
+	return nil
+}
+
+// PipeOwnedBySelf reports whether the pipe behind conn was created by this very
+// user, which is how a client recognises a daemon running as itself. Ownership it
+// cannot read is reported as false.
+func PipeOwnedBySelf(conn net.Conn) bool {
+	fdConn, ok := conn.(interface{ Fd() uintptr })
+	if !ok {
+		return false
+	}
+
+	owner, err := pipeOwnerSID(windows.Handle(fdConn.Fd()))
+	if err != nil {
+		log.Debugf("read daemon pipe owner: %v", err)
+		return false
+	}
+	return selfKnown && selfIdentity.SID != "" && owner == selfIdentity.SID
+}
+
+// pipeOwnerSID reads the owner of the pipe object a client is connected to. The
+// handle was opened with GENERIC_READ, which includes READ_CONTROL, so no extra
+// access is needed.
+func pipeOwnerSID(handle windows.Handle) (string, error) {
+	sd, err := windows.GetSecurityInfo(handle, windows.SE_KERNEL_OBJECT, windows.OWNER_SECURITY_INFORMATION)
+	if err != nil {
+		return "", fmt.Errorf("read pipe security info: %w", err)
+	}
+
+	owner, _, err := sd.Owner()
+	if err != nil {
+		return "", fmt.Errorf("read pipe owner: %w", err)
+	}
+	return owner.String(), nil
+}
+
+// trustedPipeOwner reports whether a pipe's owner is a principal a client may
+// speak to. An elevated process's objects are owned by BUILTIN\Administrators by
+// default, an unelevated one's by the user, which is why both forms appear here.
+func trustedPipeOwner(owner string) bool {
+	switch owner {
+	case sidLocalSystem, sidLocalService, sidNetworkService, sidAdministrators:
+		return true
+	}
+	return selfKnown && selfIdentity.SID != "" && owner == selfIdentity.SID
+}

client/internal/ipcauth/privileged.go

@@ -0,0 +1,125 @@
+package ipcauth
+
+import (
+	"os"
+	"runtime"
+)
+
+// Fields of the ErrorInfo detail the daemon attaches to a PermissionDenied it
+// raises for an operation that requires root/administrator. Clients match on
+// Reason and Domain rather than on the message text, and render the summary and
+// command themselves so the user gets guidance instead of a gRPC error dump.
+const (
+	// ErrorReasonPrivilegeRequired identifies the detail.
+	ErrorReasonPrivilegeRequired = "PRIVILEGE_REQUIRED"
+	// ErrorDomain scopes the reason to the NetBird daemon.
+	ErrorDomain = "daemon.netbird.io"
+	// ErrorMetaSummary is the one-sentence explanation of what was refused.
+	ErrorMetaSummary = "summary"
+	// ErrorMetaCommand is the command that performs the same operation with the
+	// privileges it needs, ready to copy and run.
+	ErrorMetaCommand = "command"
+)
+
+// The identity of the process evaluating callers, captured once because it cannot
+// change. selfKnown is false when it could not be read, in which case nothing is
+// ever treated as this process. selfMayDelegate additionally requires this
+// process to be unprivileged: see IsPrivilegedCaller.
+var (
+	selfIdentity    Identity
+	selfKnown       bool
+	selfMayDelegate bool
+	// selfPID is this process's PID, used to recognise the daemon dialling itself.
+	selfPID = os.Getpid()
+)
+
+func init() {
+	id, err := CurrentProcessIdentity()
+	if err != nil {
+		return
+	}
+	selfIdentity, selfKnown = id, true
+	// Only an unprivileged daemon delegates its authority to its own identity.
+	// When it is root or LocalSystem, sharing its identity does not mean sharing
+	// its power: on Windows a filtered and a full token carry the same SID, so
+	// matching there would let a non-elevated shell of an administrator account
+	// act as an administrator, which is the boundary the token check exists to
+	// keep.
+	selfMayDelegate = !id.IsPrivileged()
+}
+
+// IsDaemonSelf reports whether an identity is this very process. The JSON gateway
+// runs inside the daemon and re-dials it locally, so this is what distinguishes
+// the gateway from any other caller, whatever user the daemon runs as.
+func IsDaemonSelf(id Identity) bool {
+	if !selfKnown || id.IsWindows() != selfIdentity.IsWindows() {
+		return false
+	}
+	if id.IsWindows() {
+		return id.SID != "" && id.SID == selfIdentity.SID
+	}
+	return id.UID == selfIdentity.UID
+}
+
+// IsPrivilegedCaller reports whether an identity may make the changes the daemon
+// restricts to the platform administrator. This is the daemon's own rule and
+// cannot be evaluated by a client, which does not know what the daemon runs as.
+//
+// Beyond root/administrator it accepts a caller running as the daemon's own
+// identity when the daemon is itself unprivileged. That keeps a rootless container
+// working, where there is no uid 0 at all, and a Windows daemon in netstack mode,
+// which needs no administrator rights. In those setups a caller sharing the
+// daemon's identity can already rewrite the config files it reads and replace the
+// binary it runs, so refusing it a config change would protect nothing; and an
+// unprivileged daemon cannot hand out a root shell in the first place.
+func IsPrivilegedCaller(id Identity) bool {
+	if id.IsPrivileged() {
+		return true
+	}
+	return selfMayDelegate && IsDaemonSelf(id)
+}
+
+// SelfDelegatesTo returns the identity this process delegates its authority to,
+// and whether it delegates at all. Only an unprivileged daemon does: see
+// IsPrivilegedCaller. It exists so a refusal can name who may actually perform the
+// operation, because on such a host root is neither required nor necessarily
+// available.
+func SelfDelegatesTo() (Identity, bool) {
+	if !selfKnown || !selfMayDelegate {
+		return Identity{}, false
+	}
+	return selfIdentity, true
+}
+
+// PrivilegedActor names the principal a privileged operation requires, for use
+// in messages shown to the user.
+func PrivilegedActor() string {
+	if runtime.GOOS == "windows" {
+		return "administrator privileges"
+	}
+	return "root"
+}
+
+// ElevatedCommand renders a command so that running it grants the privileges the
+// operation needs. Windows has no in-line equivalent of sudo, so the command is
+// returned unchanged and the user is expected to run it from an elevated
+// terminal.
+func ElevatedCommand(command string) string {
+	if runtime.GOOS == "windows" {
+		return command
+	}
+	return "sudo " + command
+}
+
+// UpCommand renders an elevated `netbird up` with the given flags, preceded by a
+// `down`. The down is what makes the command work on a connected client: `netbird
+// up` prints "Already connected" and returns without applying any config flag, so
+// on its own the command would appear to do nothing. It is a no-op, exit 0, when
+// the client is not connected.
+//
+// ";" rather than "&&" so the line can be pasted into any of the shells a user
+// might have: PowerShell 5.1, still the default on Windows Server, rejects "&&"
+// as a syntax error.
+func UpCommand(flags string) string {
+	return ElevatedCommand("netbird down") + "; " + ElevatedCommand("netbird up "+flags)
+}

client/internal/ipcauth/privileged_test.go

@@ -0,0 +1,134 @@
+package ipcauth
+
+import "testing"
+
+// The self rule is the one place privilege is granted to something other than the
+// platform administrator, so its two guards matter: it must apply only when the
+// daemon is itself unprivileged, and only to a caller with the daemon's identity.
+func TestIsPrivilegedCaller_SelfRule(t *testing.T) {
+	tests := []struct {
+		name string
+		// self stands in for the process the daemon runs as.
+		self      Identity
+		selfKnown bool
+		caller    Identity
+		want      bool
+	}{
+		{
+			name:      "root is privileged whatever the daemon runs as",
+			self:      Identity{UID: 1000},
+			selfKnown: true,
+			caller:    Identity{UID: 0},
+			want:      true,
+		},
+		{
+			name:      "an unprivileged daemon delegates to its own user (rootless container)",
+			self:      Identity{UID: 1000},
+			selfKnown: true,
+			caller:    Identity{UID: 1000},
+			want:      true,
+		},
+		{
+			name:      "an unprivileged daemon delegates to nobody else",
+			self:      Identity{UID: 1000},
+			selfKnown: true,
+			caller:    Identity{UID: 1001},
+			want:      false,
+		},
+		{
+			// The daemon is root on a normal install, so sharing its identity is
+			// already covered by being root; nothing else may match.
+			name:      "a root daemon delegates to nobody",
+			self:      Identity{UID: 0},
+			selfKnown: true,
+			caller:    Identity{UID: 1000},
+			want:      false,
+		},
+		{
+			// Windows netstack mode: the daemon needs no administrator rights.
+			name:      "an unprivileged windows daemon delegates to its own SID",
+			self:      Identity{SID: "S-1-5-21-1-2-3-1001"},
+			selfKnown: true,
+			caller:    Identity{SID: "S-1-5-21-1-2-3-1001"},
+			want:      true,
+		},
+		{
+			name:      "an unprivileged windows daemon delegates to no other SID",
+			self:      Identity{SID: "S-1-5-21-1-2-3-1001"},
+			selfKnown: true,
+			caller:    Identity{SID: "S-1-5-21-1-2-3-1002"},
+			want:      false,
+		},
+		{
+			// The UAC boundary: a filtered and a full token of the same account
+			// carry the same SID but not the same power, so an elevated daemon must
+			// never delegate to its own SID.
+			name:      "an elevated windows daemon does not delegate to its own SID",
+			self:      Identity{SID: "S-1-5-21-1-2-3-500", Elevated: true},
+			selfKnown: true,
+			caller:    Identity{SID: "S-1-5-21-1-2-3-500"},
+			want:      false,
+		},
+		{
+			name:      "LocalSystem is privileged on its own merits, not by delegation",
+			self:      Identity{SID: sidLocalSystem},
+			selfKnown: true,
+			caller:    Identity{SID: sidLocalSystem},
+			want:      true, // LocalSystem is privileged on its own merits
+		},
+		{
+			name:      "identities of different kinds never match",
+			self:      Identity{UID: 1000},
+			selfKnown: true,
+			caller:    Identity{SID: "S-1-5-21-1-2-3-1001"},
+			want:      false,
+		},
+		{
+			name:      "an unknown self identity delegates to nobody",
+			self:      Identity{},
+			selfKnown: false,
+			caller:    Identity{UID: 1000},
+			want:      false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			prevID, prevKnown, prevDelegate := selfIdentity, selfKnown, selfMayDelegate
+			t.Cleanup(func() { selfIdentity, selfKnown, selfMayDelegate = prevID, prevKnown, prevDelegate })
+
+			selfIdentity, selfKnown = tt.self, tt.selfKnown
+			selfMayDelegate = tt.selfKnown && !tt.self.IsPrivileged()
+
+			if got := IsPrivilegedCaller(tt.caller); got != tt.want {
+				t.Fatalf("IsPrivilegedCaller(%v) with daemon %v = %t, want %t",
+					tt.caller, tt.self, got, tt.want)
+			}
+		})
+	}
+}
+
+// The real process must never accidentally delegate: a test binary running as a
+// normal user is unprivileged, so it may match itself, but nothing else.
+func TestIsPrivilegedCaller_ThisProcess(t *testing.T) {
+	id, err := CurrentProcessIdentity()
+	if err != nil {
+		t.Skipf("cannot read this process's identity: %v", err)
+	}
+
+	// This process is always allowed to act as itself: either it is privileged, or
+	// it is unprivileged and therefore delegates to its own identity.
+	if !IsPrivilegedCaller(id) {
+		t.Errorf("this process %v was refused its own identity", id)
+	}
+
+	// A caller that is neither root nor this process must be refused, whatever
+	// this process happens to be.
+	other := Identity{UID: id.UID + 1}
+	if id.IsWindows() {
+		other = Identity{SID: id.SID + "9"}
+	}
+	if IsPrivilegedCaller(other) {
+		t.Errorf("an unrelated identity %v was treated as privileged", other)
+	}
+}

client/internal/ipcauth/self_unix.go

@@ -0,0 +1,17 @@
+//go:build !windows
+
+package ipcauth
+
+import "os"
+
+// CurrentProcessIdentity returns this process's identity as the daemon would
+// see it if this process connected to the local IPC. It lets a client (the UI)
+// decide up front whether a privileged operation can succeed, without a
+// round-trip and without duplicating the rules: the answer comes from the same
+// Identity.IsPrivileged the daemon applies.
+func CurrentProcessIdentity() (Identity, error) {
+	return Identity{
+		UID: uint32(os.Geteuid()),
+		GID: uint32(os.Getegid()),
+	}, nil
+}

client/internal/ipcauth/self_windows.go

@@ -0,0 +1,35 @@
+//go:build windows
+
+package ipcauth
+
+import (
+	"fmt"
+
+	"golang.org/x/sys/windows"
+)
+
+// CurrentProcessIdentity returns this process's identity as the daemon would see
+// it if this process connected to the local IPC. It lets a client (the UI)
+// decide up front whether a privileged operation can succeed, without a
+// round-trip and without duplicating the rules: the answer comes from the same
+// Identity.IsPrivileged the daemon applies to the token it reads off the pipe.
+func CurrentProcessIdentity() (Identity, error) {
+	// A pseudo-token, so it must not be closed.
+	token := windows.GetCurrentProcessToken()
+
+	user, err := token.GetTokenUser()
+	if err != nil {
+		return Identity{}, fmt.Errorf("read token user: %w", err)
+	}
+
+	groups, err := tokenGroupSIDs(token)
+	if err != nil {
+		return Identity{}, err
+	}
+
+	return Identity{
+		SID:      user.User.Sid.String(),
+		Groups:   groups,
+		Elevated: token.IsElevated(),
+	}, nil
+}

client/internal/profilemanager/config.go

@@ -746,6 +746,13 @@ func (config *Config) applyMDMPolicy(policy *mdm.Policy) {
 // appended for https or ":80" for http. The serviceName parameter is
 // used to contextualise error messages. On success returns the parsed
 // *url.URL; on failure returns a non-nil error.
+// ParseServiceURL normalises a service URL exactly as the config layer does when
+// it stores one, so callers comparing a requested URL against a stored one do not
+// have to reimplement the scheme validation and default-port handling.
+func ParseServiceURL(serviceName, serviceURL string) (*url.URL, error) {
+	return parseURL(serviceName, serviceURL)
+}
+
 func parseURL(serviceName, serviceURL string) (*url.URL, error) {
 	parsedMgmtURL, err := url.ParseRequestURI(serviceURL)
 	if err != nil {