fix: harden generated Windows wrapper ACLs

internal/client/supervisor/windows/native_exec.go

@@ -252,7 +252,7 @@ func (process *execProcess) startReaders(maxChunk uint64, remove func()) {
 	}()
 }
 
-func materializeWrapper(directory string, wrapper Wrapper, now time.Time) (string, func(), error) {
+func materializeWrapper(directory string, wrapper Wrapper, now time.Time, secure func(string) error) (string, func(), error) {
 	if directory == "" {
 		return "", nil, ErrInvalidWorkingDirectory
 	}
@@ -272,6 +272,12 @@ func materializeWrapper(directory string, wrapper Wrapper, now time.Time) (strin
 		cleanup()
 		return "", nil, err
 	}
+	if secure != nil {
+		if err := secure(temporaryName); err != nil {
+			cleanup()
+			return "", nil, err
+		}
+	}
 	if _, err := temporary.Write(wrapper.Bytes); err != nil {
 		cleanup()
 		return "", nil, err
@@ -379,7 +385,7 @@ func (manager *execSupervisor) startPortable(ctx context.Context, spec superviso
 		if err != nil {
 			return nil, err
 		}
-		wrapperPath, cleanup, err = materializeWrapper(spec.WorkingDirectory, wrapper, manager.options.Now())
+		wrapperPath, cleanup, err = materializeWrapper(spec.WorkingDirectory, wrapper, manager.options.Now(), nil)
 		if err != nil {
 			return nil, err
 		}

internal/client/supervisor/windows/native_windows.go

@@ -87,10 +87,7 @@ func (manager *execSupervisor) Start(ctx context.Context, spec supervisor.StartS
 	if err != nil {
 		return nil, err
 	}
-	wrapperPath, cleanup, err := materializeWrapper(spec.WorkingDirectory, wrapper, manager.options.Now())
+	var cleanup func()
-	if err != nil {
-		return nil, err
-	}
 	fail := func(cause error) (supervisor.Process, error) {
 		if cleanup != nil {
 			cleanup()
@@ -103,6 +100,12 @@ func (manager *execSupervisor) Start(ctx context.Context, spec supervisor.StartS
 		return fail(err)
 	}
 	defer token.Close()
+	wrapperPath, cleanup, err := materializeWrapper(spec.WorkingDirectory, wrapper, manager.options.Now(), func(path string) error {
+		return secureWrapperFile(path, identity.UserSID)
+	})
+	if err != nil {
+		return fail(err)
+	}
 	baseEnvironment, err := token.Environ(false)
 	if err != nil {
 		return fail(fmt.Errorf("build token environment: %w", err))
@@ -264,6 +267,50 @@ func verifyExecutable(path string) error {
 	return nil
 }
 
+// secureWrapperFile replaces the inherited directory ACL with a protected
+// DACL. The service writes the wrapper before this call; afterward only
+// LocalSystem and the selected effective token SID can read it. This is done
+// after token selection so active-user commands do not depend on inherited
+// broad ProgramData permissions.
+func secureWrapperFile(path, effectiveSID string) error {
+	systemSID, err := winapi.StringToSid(securitySystemRID)
+	if err != nil {
+		return err
+	}
+	effective := systemSID
+	if effectiveSID != "" && effectiveSID != securitySystemRID {
+		effective, err = winapi.StringToSid(effectiveSID)
+		if err != nil {
+			return err
+		}
+	}
+	entries := []winapi.EXPLICIT_ACCESS{{
+		AccessPermissions: winapi.GENERIC_ALL,
+		AccessMode:        winapi.SET_ACCESS,
+		Trustee: winapi.TRUSTEE{
+			TrusteeForm:  winapi.TRUSTEE_IS_SID,
+			TrusteeType:  winapi.TRUSTEE_IS_WELL_KNOWN_GROUP,
+			TrusteeValue: winapi.TrusteeValueFromSID(systemSID),
+		},
+	}}
+	if effective != systemSID {
+		entries = append(entries, winapi.EXPLICIT_ACCESS{
+			AccessPermissions: winapi.GENERIC_READ,
+			AccessMode:        winapi.SET_ACCESS,
+			Trustee: winapi.TRUSTEE{
+				TrusteeForm:  winapi.TRUSTEE_IS_SID,
+				TrusteeType:  winapi.TRUSTEE_IS_USER,
+				TrusteeValue: winapi.TrusteeValueFromSID(effective),
+			},
+		})
+	}
+	acl, err := winapi.ACLFromEntries(entries, nil)
+	if err != nil {
+		return err
+	}
+	return winapi.SetNamedSecurityInfo(path, winapi.SE_FILE_OBJECT, winapi.OWNER_SECURITY_INFORMATION|winapi.DACL_SECURITY_INFORMATION|winapi.PROTECTED_DACL_SECURITY_INFORMATION, systemSID, nil, acl, nil)
+}
+
 func createStandardPipes() (*os.File, *os.File, *os.File, *os.File, *os.File, *os.File, error) {
 	security := &winapi.SecurityAttributes{Length: uint32(unsafe.Sizeof(winapi.SecurityAttributes{})), InheritHandle: 1}
 	var stdinReadHandle, stdinWriteHandle winapi.Handle
@@ -559,7 +606,7 @@ func openTokenForAttempt(contextName ExecutionContext, candidate *SessionCandida
 		if err != nil {
 			return 0, supervisor.EffectiveIdentity{}, err
 		}
-		return token, supervisor.EffectiveIdentity{Context: string(ContextLocalService), Elevated: false, Integrity: "medium"}, nil
+		return token, supervisor.EffectiveIdentity{Context: string(ContextLocalService), UserSID: securityLocalServiceRID, Elevated: false, Integrity: "medium"}, nil
 	case ContextLocalSystem:
 		return duplicateServiceToken()
 	default: