Read user certificates only from the session of the active profile's owner

client/internal/certproof/README.md

@@ -88,8 +88,11 @@ cmd.SysProcAttr = &syscall.SysProcAttr{Token: syscall.Token(token), CreationFlag
 `CREATE_NO_WINDOW` matters: without it a console window flashes on the user's desktop on
 every sync.
 
-Session selection prefers the physical console, then falls back to any active session,
-so remote desktop and VDI hosts work. `WTSQueryUserToken` needs `SE_TCB_NAME`, which
+The session asked is one belonging to the account that owns the active profile, matched
+by SID: the console first, then active remote sessions, then disconnected ones, whose
+user is still signed in. Session 0 hosts services and is never asked. A profile without
+an owner asks the console user only. Nobody else who happens to be signed in to a
+terminal server or VDI host can therefore decide the result. `WTSQueryUserToken` needs `SE_TCB_NAME`, which
 LocalSystem holds and an ordinary process does not, so a user-run `netbird up` skips the
 helper and reads the machine store alone.
 
@@ -221,11 +224,11 @@ currently open**. Consequences worth designing around:
 - **Signing out changes the answer.** Posture can flip between compliant and
   non-compliant across a sign-out, so management should treat "no proof" as its own
   state rather than as a failed check, or users get disconnected at the sign-in screen.
-- **One session is asked, not all of them.** macOS asks the console user, so other
-  fast-user-switched accounts are skipped even though their keychains are unlocked.
-  Windows prefers the console and otherwise takes the first active session. If you ever
-  need every signed-in user, both platforms would have to enumerate sessions and ask
-  each one.
+- **Only the profile owner is asked.** The user certificate belongs to whoever owns the
+  active NetBird profile. macOS asks the console user only when that user owns the
+  profile, so a fast-user-switched account never answers for someone else. Windows asks
+  a session of the owner wherever it is, console or remote, and with no owner recorded
+  only the console user.
 - **A locked keychain still blocks signing.** A user can be logged in with their
   keychain locked (locked on sleep, or manually). The helper then needs an unlock prompt
   and may block, which is why the spawn has a 30s timeout and a failure is reported as

client/internal/certproof/collect_darwin.go

@@ -23,7 +23,7 @@ const helperTimeout = 30 * time.Second
 // installs device identities, and reaches the console user's login keychain only by
 // launching a helper into that user's session. A Mac sitting at the login window
 // therefore yields device proofs alone.
-func CollectProofs(ctx context.Context, checks []*proto.Checks, peerKey []byte, _ Config) []certposture.Proof {
+func CollectProofs(ctx context.Context, checks []*proto.Checks, peerKey []byte, cfg Config) []certposture.Proof {
 	challenges := certificateChallenges(checks)
 	if len(challenges) == 0 {
 		logNoChallenges(checks)
@@ -38,7 +38,7 @@ func CollectProofs(ctx context.Context, checks []*proto.Checks, peerKey []byte,
 
 	proofs := CollectChallenges(ctx, DefaultStore(), challenges, peerKey)
 
-	userProofs, err := collectAsConsoleUser(ctx, challenges, peerKey)
+	userProofs, err := collectAsConsoleUser(ctx, cfg.ProfileOwner, challenges, peerKey)
 	if err != nil {
 		log.Debugf("certificate posture: console user keychain unavailable: %v", err)
 	}
@@ -49,11 +49,15 @@ func CollectProofs(ctx context.Context, checks []*proto.Checks, peerKey []byte,
 // user. Dropping to their uid is not enough: keychain access is an XPC call to a
 // per-session securityd, so the helper has to enter their Mach bootstrap namespace,
 // which is what launchctl asuser does.
-func collectAsConsoleUser(ctx context.Context, challenges []*proto.CertificateChallenge, peerKey []byte) ([]certposture.Proof, error) {
+func collectAsConsoleUser(ctx context.Context, owner string, challenges []*proto.CertificateChallenge, peerKey []byte) ([]certposture.Proof, error) {
 	user, ok := CurrentConsoleUser()
 	if !ok {
 		return nil, nil
 	}
+	if !user.isOwner(owner) {
+		log.Debugf("certificate posture: console user %s does not own the active profile, no user keychain is asked", user.Name)
+		return nil, nil
+	}
 
 	binary, err := os.Executable()
 	if err != nil {

client/internal/certproof/collect_windows.go

@@ -22,7 +22,7 @@ const helperTimeout = 30 * time.Second
 // Intune enrol device certificates, and reaches the signed-in user's store by launching
 // a helper with that session's token. A machine at the sign-in screen therefore proves
 // device certificates alone.
-func CollectProofs(ctx context.Context, checks []*proto.Checks, peerKey []byte, _ Config) []certposture.Proof {
+func CollectProofs(ctx context.Context, checks []*proto.Checks, peerKey []byte, cfg Config) []certposture.Proof {
 	challenges := certificateChallenges(checks)
 	if len(challenges) == 0 {
 		logNoChallenges(checks)
@@ -37,7 +37,7 @@ func CollectProofs(ctx context.Context, checks []*proto.Checks, peerKey []byte,
 		return proofs
 	}
 
-	userProofs, err := collectAsDesktopUser(ctx, challenges, peerKey)
+	userProofs, err := collectAsDesktopUser(ctx, cfg.ProfileOwner, challenges, peerKey)
 	if err != nil {
 		log.Debugf("certificate posture: user certificate store unavailable: %v", err)
 	}
@@ -53,8 +53,8 @@ func helperStore() Store {
 // collectAsDesktopUser runs the helper inside the interactive session of the signed-in
 // user. Unlike a keychain on macOS, a Windows service can assume a user identity
 // directly, so the session token goes straight into the child process.
-func collectAsDesktopUser(ctx context.Context, challenges []*proto.CertificateChallenge, peerKey []byte) ([]certposture.Proof, error) {
-	user, ok := CurrentDesktopUser()
+func collectAsDesktopUser(ctx context.Context, owner string, challenges []*proto.CertificateChallenge, peerKey []byte) ([]certposture.Proof, error) {
+	user, ok := CurrentDesktopUser(owner)
 	if !ok {
 		return nil, nil
 	}

client/internal/certproof/consoleuser_darwin.go

@@ -5,6 +5,7 @@ package certproof
 import (
 	"bytes"
 	"fmt"
+	"strconv"
 	"sync"
 
 	"github.com/ebitengine/purego"
@@ -69,6 +70,13 @@ func (u ConsoleUser) hasDesktop() bool {
 	return u.UID != 0
 }
 
+// isOwner reports whether the console user is owner, the account of the active profile,
+// which is recorded as a short user name or, for an account without one, a numeric uid.
+// With no owner the console user counts, as macOS has a single console user.
+func (u ConsoleUser) isOwner(owner string) bool {
+	return owner == "" || owner == u.Name || owner == strconv.FormatUint(uint64(u.UID), 10)
+}
+
 func cfString(str uintptr) string {
 	buf := make([]byte, consoleNameBufSize)
 	if !cfStringGetCString(str, &buf[0], len(buf), encodingUTF8) {

client/internal/certproof/consoleuser_darwin_test.go

@@ -39,3 +39,13 @@ func TestCurrentConsoleUser_AgreesWithItself(t *testing.T) {
 	assert.NotZero(t, user.UID, "a desktop session never belongs to uid 0")
 	assert.True(t, user.hasDesktop(), "a reported console user must be a desktop session")
 }
+
+func TestConsoleUser_IsOwner(t *testing.T) {
+	user := ConsoleUser{Name: "maycon", UID: 501, GID: 20}
+
+	assert.True(t, user.isOwner(""), "a profile without owner accepts the single console user")
+	assert.True(t, user.isOwner("maycon"), "the owner by short name")
+	assert.True(t, user.isOwner("501"), "the owner recorded as a numeric uid")
+	assert.False(t, user.isOwner("viktor"), "another account's profile must not read this user's keychain")
+	assert.False(t, user.isOwner("502"), "another uid is another account")
+}

client/internal/certproof/desktopuser_windows.go

@@ -2,6 +2,7 @@ package certproof
 
 import (
 	"fmt"
+	"strings"
 	"unsafe"
 
 	log "github.com/sirupsen/logrus"
@@ -10,11 +11,14 @@ import (
 
 const (
 	noActiveSession = 0xFFFFFFFF
+	servicesSession = 0
 
-	// wtsCurrentServer is WTS_CURRENT_SERVER_HANDLE and wtsActive is WTSActive of
-	// WTS_CONNECTSTATE_CLASS. Neither is exported by x/sys/windows.
+	// wtsCurrentServer is WTS_CURRENT_SERVER_HANDLE; wtsActive and wtsDisconnected are
+	// WTSActive and WTSDisconnected of WTS_CONNECTSTATE_CLASS. None is exported by
+	// x/sys/windows.
 	wtsCurrentServer = windows.Handle(0)
 	wtsActive        = 0
+	wtsDisconnected  = 4
 )
 
 // DesktopUser is an interactive session and the account signed into it. The user's
@@ -33,37 +37,91 @@ func (u DesktopUser) Close() {
 	}
 }
 
-// CurrentDesktopUser returns a token for the interactive user whose certificate store
-// should be asked. The physical console comes first, and an active remote desktop
-// session is used when nobody is at the console, which is how servers and VDI hosts are
-// normally reached. The second return is false at the sign-in screen, where no
-// interactive session exists and only machine certificates can be proven.
+// CurrentDesktopUser returns a token for the session whose certificate store should be
+// asked: a session of owner, the account the active profile belongs to, with the
+// physical console preferred over remote sessions. With no owner only the console user
+// counts. Picking any signed-in user instead would let whoever else is logged in to a
+// terminal server or VDI host decide the result. The second return is false when no
+// such session exists, and only machine certificates can then be proven.
 //
 // Obtaining the token needs SE_TCB_NAME, which the LocalSystem service has and an
 // ordinary process does not.
-func CurrentDesktopUser() (DesktopUser, bool) {
-	if session := windows.WTSGetActiveConsoleSessionId(); session != noActiveSession {
-		if user, ok := desktopUser(session); ok {
-			return user, true
-		}
-		log.Debugf("console session %d has nobody signed in, looking for an active remote session", session)
+func CurrentDesktopUser(owner string) (DesktopUser, bool) {
+	console := windows.WTSGetActiveConsoleSessionId()
+	if owner == "" {
+		return consoleUser(console)
 	}
 
-	sessions, err := activeSessions()
+	match, err := ownerMatcher(owner)
+	if err != nil {
+		log.Debugf("certificate posture: %v", err)
+		return DesktopUser{}, false
+	}
+
+	sessions, err := userSessions(console)
 	if err != nil {
 		log.Debugf("cannot enumerate terminal sessions: %v", err)
 		return DesktopUser{}, false
 	}
 	for _, session := range sessions {
-		if user, ok := desktopUser(session); ok {
+		user, ok := desktopUser(session)
+		if !ok {
+			continue
+		}
+		if match(user) {
 			return user, true
 		}
+		user.Close()
 	}
 
-	log.Debug("no interactive session is signed in, no user certificate store is reachable")
+	log.Debugf("certificate posture: profile owner %s has no signed-in session, no user certificate store is reachable", owner)
 	return DesktopUser{}, false
 }
 
+func consoleUser(console uint32) (DesktopUser, bool) {
+	if console == noActiveSession || console == servicesSession {
+		log.Debug("no console session, no user certificate store is reachable")
+		return DesktopUser{}, false
+	}
+	user, ok := desktopUser(console)
+	if !ok {
+		log.Debugf("console session %d has nobody signed in, no user certificate store is reachable", console)
+	}
+	return user, ok
+}
+
+// ownerMatcher reports whether a session user is owner. Accounts are compared by SID,
+// which is what identifies a Windows account; the name comparison is a fallback for an
+// owner name that no longer resolves, and is case-insensitive like Windows account names.
+func ownerMatcher(owner string) (func(DesktopUser) bool, error) {
+	ownerSID, _, _, err := windows.LookupSID("", owner)
+	if err != nil {
+		log.Debugf("certificate posture: resolving profile owner %s: %v, matching by name", owner, err)
+		return func(user DesktopUser) bool { return sameAccountName(user.Name, owner) }, nil
+	}
+	return func(user DesktopUser) bool {
+		tokenUser, err := user.Token.GetTokenUser()
+		if err != nil {
+			log.Debugf("failed reading token user of session %d: %v", user.Session, err)
+			return false
+		}
+		return tokenUser.User.Sid.Equals(ownerSID)
+	}, nil
+}
+
+// sameAccountName compares DOMAIN\account names case-insensitively, and an owner given
+// without a domain against the account part alone.
+func sameAccountName(sessionName, owner string) bool {
+	if strings.EqualFold(sessionName, owner) {
+		return true
+	}
+	if strings.Contains(owner, `\`) {
+		return false
+	}
+	_, account, found := strings.Cut(sessionName, `\`)
+	return found && strings.EqualFold(account, owner)
+}
+
 func desktopUser(session uint32) (DesktopUser, bool) {
 	var token windows.Token
 	if err := windows.WTSQueryUserToken(session, &token); err != nil {
@@ -97,7 +155,10 @@ func tokenAccount(token windows.Token) (string, error) {
 	return domain + `\` + account, nil
 }
 
-func activeSessions() ([]uint32, error) {
+// userSessions lists the sessions a user can be signed in to, console first, then
+// active remote sessions, then disconnected ones, whose user is still signed in. Session
+// 0 is skipped: it hosts services and never belongs to an interactive user.
+func userSessions(console uint32) ([]uint32, error) {
 	var info *windows.WTS_SESSION_INFO
 	var count uint32
 	if err := windows.WTSEnumerateSessions(wtsCurrentServer, 0, 1, &info, &count); err != nil {
@@ -105,13 +166,19 @@ func activeSessions() ([]uint32, error) {
 	}
 	defer windows.WTSFreeMemory(uintptr(unsafe.Pointer(info)))
 
-	var active []uint32
-	for _, session := range unsafe.Slice(info, count) {
-		if session.State == wtsActive {
-			active = append(active, session.SessionID)
+	var sessions []uint32
+	if console != noActiveSession && console != servicesSession {
+		sessions = append(sessions, console)
+	}
+	for _, state := range []uint32{wtsActive, wtsDisconnected} {
+		for _, session := range unsafe.Slice(info, count) {
+			if session.SessionID == servicesSession || session.SessionID == console || session.State != state {
+				continue
+			}
+			sessions = append(sessions, session.SessionID)
 		}
 	}
-	return active, nil
+	return sessions, nil
 }
 
 // runningAsLocalSystem reports whether this process is the service. The helper runs as

client/internal/certproof/desktopuser_windows_test.go

@@ -0,0 +1,35 @@
+package certproof
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSameAccountName(t *testing.T) {
+	tests := []struct {
+		session, owner string
+		want           bool
+	}{
+		{`CORP\alice`, `CORP\alice`, true},
+		{`CORP\alice`, `corp\ALICE`, true},
+		{`CORP\alice`, `alice`, true},
+		{`CORP\alice`, `OTHER\alice`, false},
+		{`CORP\alice`, `bob`, false},
+		{`alice`, `alice`, true},
+		{`CORP\alice`, `CORP\alic`, false},
+	}
+	for _, tt := range tests {
+		assert.Equal(t, tt.want, sameAccountName(tt.session, tt.owner), "session %q, owner %q", tt.session, tt.owner)
+	}
+}
+
+// CurrentDesktopUser against the real session manager: an owner no session belongs to
+// must never yield a session, whoever else is signed in.
+func TestCurrentDesktopUser_UnknownOwnerHasNoSession(t *testing.T) {
+	user, ok := CurrentDesktopUser(`NO-SUCH-DOMAIN\no-such-user-netbird`)
+	if ok {
+		user.Close()
+	}
+	assert.False(t, ok, "a profile owner without a session must not borrow another user's store")
+}

client/internal/certproof/store.go

@@ -47,12 +47,18 @@ type Store interface {
 	Candidates(ctx context.Context) ([]Candidate, error)
 }
 
-// Config selects where the Linux daemon looks for certificates: Dir is the PEM directory,
+// Config selects where the daemon looks for certificates. Dir is the Linux PEM directory,
 // empty for NB_CERT_STORE_DIR or /etc/netbird/certs, and PKCS11 names a token whose keys
 // sign for certificates on the token or in that directory.
+//
+// ProfileOwner is the OS account the active profile belongs to. On macOS and Windows only
+// that account's certificate store is consulted for user certificates, so on a machine
+// with several people signed in the result does not depend on who else is logged in.
+// Empty means the profile has no owner, and only the user at the physical console counts.
 type Config struct {
-	Dir    string
-	PKCS11 PKCS11Config
+	Dir          string
+	PKCS11       PKCS11Config
+	ProfileOwner string
 }
 
 func (c Config) dir() string {

client/internal/connect.go

@@ -76,6 +76,8 @@ type ConnectClient struct {
 	// netMgr gates every reconnection loop on OS-reported network
 	// availability and sweeps connections on network change.
 	netMgr *netevents.Manager
+
+	profileOwner string
 }
 
 // ConnectClientOption configures optional ConnectClient behavior.
@@ -86,6 +88,12 @@ func WithNetEvents(events *netevents.Manager) ConnectClientOption {
 	return func(c *ConnectClient) { c.netMgr = events }
 }
 
+// WithProfileOwner names the OS account the active profile belongs to, whose own
+// certificate store answers user certificate posture checks.
+func WithProfileOwner(username string) ConnectClientOption {
+	return func(c *ConnectClient) { c.profileOwner = username }
+}
+
 func NewConnectClient(
 	ctx context.Context,
 	config *profilemanager.Config,
@@ -417,6 +425,7 @@ func (c *ConnectClient) run(mobileDependency MobileDependency, runningChan chan
 			return wrapErr(err)
 		}
 		engineConfig.TempDir = mobileDependency.TempDir
+		engineConfig.CertStore.ProfileOwner = c.profileOwner
 		// Leave StateDir empty when there is no state path so a disk-backed
 		// syncstore falls back to os.TempDir() instead of filepath.Dir("") == ".".
 		if path != "" {

client/server/server.go

@@ -2515,9 +2515,23 @@ func (s *Server) checkDisableAdvancedView() *bool {
 	return nil
 }
 
+// profileOwnerOption passes the OS account of the active profile to the connect client,
+// which reads that account's certificate store for user certificate posture checks.
+func (s *Server) profileOwnerOption() []internal.ConnectClientOption {
+	if s.profileManager == nil {
+		return nil
+	}
+	activeProf, err := s.profileManager.GetActiveProfileState()
+	if err != nil {
+		log.Debugf("no active profile owner for certificate posture: %v", err)
+		return nil
+	}
+	return []internal.ConnectClientOption{internal.WithProfileOwner(activeProf.Username)}
+}
+
 func (s *Server) connect(ctx context.Context, config *profilemanager.Config, statusRecorder *peer.Status, runningChan chan struct{}) error {
 	log.Tracef("running client connection")
-	client := internal.NewConnectClient(ctx, config, statusRecorder)
+	client := internal.NewConnectClient(ctx, config, statusRecorder, s.profileOwnerOption()...)
 	client.SetUpdateManager(s.updateManager)
 	client.SetSyncResponsePersistence(s.persistSyncResponse)