diff --git a/src/ppclock/mcp_server.py b/src/ppclock/mcp_server.py
index b812a47..52f6493 100644
--- a/src/ppclock/mcp_server.py
+++ b/src/ppclock/mcp_server.py
@@ -17,8 +17,19 @@ from .mcp_tools import register_tools
 TOKEN_ENV = "PPCLOCK_MCP_TOKEN"
 
 
-def build_server(manager: DeviceManager) -> FastMCP:
-    mcp = FastMCP("ppclock", stateless_http=True)
+def build_server(manager: DeviceManager,
+                 allowed_hosts: list[str] | None = None) -> FastMCP:
+    """装配 FastMCP。allowed_hosts 为 HTTP Host 白名单（mcp DNS 重绑定防护）：
+    HTTP 模式绑非回环地址时，必须把本机的局域网地址加进来
+    （如 ["192.168.61.35:8972", "localhost:8972"]），否则 LAN Host 请求被 421。
+    None 保持 mcp 默认（仅 localhost 族）。"""
+    if allowed_hosts is not None:
+        from mcp.server.transport_security import TransportSecuritySettings
+        mcp = FastMCP("ppclock", stateless_http=True,
+                      transport_security=TransportSecuritySettings(
+                          allowed_hosts=allowed_hosts))
+    else:
+        mcp = FastMCP("ppclock", stateless_http=True)
     register_tools(mcp, manager)
     return mcp
 
@@ -34,6 +45,10 @@ def parse_args(argv=None) -> argparse.Namespace:
                    help="守候连接秒数（覆盖设备 30-60s 广播窗口）")
     p.add_argument("--idle-timeout", type=float, default=300.0,
                    help="空闲断开秒数；0=每次调用独立连接")
+    p.add_argument("--allowed-hosts", default=None,
+                   help="HTTP Host 白名单（逗号分隔）。HTTP 模式绑非回环地址时，"
+                        "把本机的局域网地址加进来，如 "
+                        "192.168.61.35:8972,localhost:8972；缺省仅 localhost 族")
     return p.parse_args(argv)
 
 
@@ -71,7 +86,9 @@ def main(argv=None) -> None:
     manager = DeviceManager(mac=args.mac,
                             connect_timeout=args.connect_timeout,
                             idle_timeout=args.idle_timeout)
-    mcp = build_server(manager)
+    allowed_hosts = (None if args.allowed_hosts is None else
+                     [h.strip() for h in args.allowed_hosts.split(",") if h.strip()])
+    mcp = build_server(manager, allowed_hosts=allowed_hosts)
     if args.transport == "stdio":
         try:
             mcp.run(transport="stdio")
diff --git a/tests/test_mcp_server.py b/tests/test_mcp_server.py
index f78095c..c672ebc 100644
--- a/tests/test_mcp_server.py
+++ b/tests/test_mcp_server.py
@@ -1,4 +1,4 @@
-"""mcp_server 测试：参数解析 + 非回环强制 token + ASGI 鉴权中间件。"""
+"""mcp_server 测试：参数解析 + 非回环强制 token + ASGI 鉴权中间件 + HTTP Host 白名单。"""
 import asyncio
 
 import pytest
@@ -25,6 +25,13 @@ class TestParseArgs:
         assert a.port == 9000 and a.mac == "AA:BB:CC:DD:EE:FF"
         assert a.connect_timeout == 120.0 and a.idle_timeout == 60.0
 
+    def test_allowed_hosts_default_none(self):
+        assert parse_args([]).allowed_hosts is None
+
+    def test_allowed_hosts_flag(self):
+        a = parse_args(["--allowed-hosts", "192.168.61.35:8972,localhost:8972"])
+        assert a.allowed_hosts == "192.168.61.35:8972,localhost:8972"
+
 
 def run_middleware(token_set, auth_header):
     """驱动 TokenAuthMiddleware，返回 (status, app_called)。"""
@@ -70,3 +77,45 @@ class TestBindGuard:
         monkeypatch.delenv(TOKEN_ENV, raising=False)
         with pytest.raises(SystemExit):
             main(["--transport", "http", "--host", "0.0.0.0"])
+
+
+class TestAllowedHosts:
+    """HTTP 模式 Host 白名单回归（Windows 实测：LAN Host 被 421 拒）。
+
+    用 starlette TestClient 驱动真实 ASGI app（含 lifespan，stateless 会话管理器
+    需要其 task group）；manager 只构造不连接，initialize 不触达设备。
+    """
+
+    LAN_HOST = "192.168.61.35:8972"
+
+    def _make_app(self):
+        from ppclock.device_manager import DeviceManager
+        from ppclock.mcp_server import build_server
+        manager = DeviceManager(mac="AA:BB:CC:DD:EE:FF")
+        mcp = build_server(manager, allowed_hosts=[self.LAN_HOST,
+                                                   "localhost:8972"])
+        return mcp.streamable_http_app()
+
+    def _initialize(self, app, host):
+        from starlette.testclient import TestClient
+        with TestClient(app) as client:
+            return client.post(
+                "/mcp",
+                headers={
+                    "Host": host,
+                    "Accept": "application/json, text/event-stream",
+                    "Content-Type": "application/json",
+                },
+                json={"jsonrpc": "2.0", "id": 1, "method": "initialize",
+                      "params": {"protocolVersion": "2025-03-26",
+                                 "capabilities": {},
+                                 "clientInfo": {"name": "test", "version": "0"}}},
+            )
+
+    def test_lan_host_not_421(self):
+        r = self._initialize(self._make_app(), self.LAN_HOST)
+        assert r.status_code != 421
+
+    def test_evil_host_421(self):
+        r = self._initialize(self._make_app(), "evil.example.com")
+        assert r.status_code == 421