fix mssql login client metadata

plugins/services/mssql_raw_test.go

@@ -0,0 +1,39 @@
+//go:build plugin_mssql || !plugin_selective
+
+package services
+
+import (
+	"bytes"
+	"encoding/binary"
+	"os"
+	"testing"
+)
+
+func TestMSSQLLogin7DoesNotExposeClientIdentity(t *testing.T) {
+	var packet bytes.Buffer
+	if err := mssqlSendLogin7(&packet, "target-host", "sa", "password"); err != nil {
+		t.Fatalf("mssqlSendLogin7() error = %v", err)
+	}
+
+	data := packet.Bytes()
+	if len(data) < 8+20 {
+		t.Fatalf("login packet too short: %d", len(data))
+	}
+
+	payload := data[8:]
+	if pid := binary.LittleEndian.Uint32(payload[16:20]); pid != 0 {
+		t.Fatalf("client pid = %d, want 0", pid)
+	}
+
+	for _, value := range []string{"fscan", "target-host"} {
+		if bytes.Contains(payload, mssqlUCS2(value)) {
+			t.Fatalf("login packet contains client-identifying value %q", value)
+		}
+	}
+
+	if hostname, err := os.Hostname(); err == nil && hostname != "" {
+		if bytes.Contains(payload, mssqlUCS2(hostname)) {
+			t.Fatalf("login packet contains local hostname %q", hostname)
+		}
+	}
+}