fix mssql login client metadata

plugins/services/mssql_raw.go

@@ -9,7 +9,6 @@ import (
 	"fmt"
 	"io"
 	"net"
-	"os"
 	"sort"
 	"time"
 	"unicode/utf16"
@@ -190,17 +189,16 @@ func mssqlParsePreloginFields(payload []byte) (map[byte][]byte, error) {
 }
 
 func mssqlSendLogin7(w io.Writer, host, username, password string) error {
-	hostname, _ := os.Hostname()
 	values := []struct {
 		text     string
 		password bool
 	}{
-		{hostname, false},
+		{"", false},
 		{username, false},
 		{password, true},
-		{"fscan", false},
-		{host, false},
-		{"fscan", false},
+		{"", false},
+		{"", false},
+		{"", false},
 		{"", false},
 		{"master", false},
 		{"", false},
@@ -233,7 +231,7 @@ func mssqlSendLogin7(w io.Writer, host, username, password string) error {
 	put32(tdsVersion74)
 	put32(tdsDefaultPacketLen)
 	put32(0)
-	put32(uint32(os.Getpid()))
+	put32(0)
 	put32(0)
 	body.WriteByte(tdsOptionUseDB | tdsOptionSetLang)
 	body.WriteByte(tdsOptionODBC)

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)
+		}
+	}
+}