diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5e649cf..c901d1f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -36,6 +36,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - [#46](https://github.com/WSH032/fastapi-proxy-lib/pull/46) - fix: don't use module-level logging methods. Thanks [@dvarrazzo](https://github.com/dvarrazzo)
 - [#49](https://github.com/WSH032/fastapi-proxy-lib/pull/49) - fix!: bump `httpx-ws >= 0.7.1` to fix frankie567/httpx-ws#29. Thanks [@WSH032](https://github.com/WSH032)!
 
+### Security
+
+- [#50](https://github.com/WSH032/fastapi-proxy-lib/pull/50) - fix(security): add `localhost` rule to `default_proxy_filter`. Thanks [@WSH032](https://github.com/WSH032)!
+
 ### Removed
 
 - [#49](https://github.com/WSH032/fastapi-proxy-lib/pull/49) - Drop support for `Python 3.8`.
diff --git a/src/fastapi_proxy_lib/core/_tool.py b/src/fastapi_proxy_lib/core/_tool.py
index 6f23b2f..685fc25 100644
--- a/src/fastapi_proxy_lib/core/_tool.py
+++ b/src/fastapi_proxy_lib/core/_tool.py
@@ -370,7 +370,12 @@ def check_http_version(
 def default_proxy_filter(url: httpx.URL) -> Union[None, str]:
     """Filter by host.
 
-    If the host of url is ip address, which is not global ip address, then will reject it.
+    Reject the following hosts:
+
+    - if the host is ip address, and is not global ip address. e.g:
+        - `http://127.0.0.1`
+        - `http://192.168.0.1`
+    - if the host contains "localhost".
 
     Warning:
         It will consumption time: 3.22~4.7 µs ± 42.6 ns.
@@ -383,8 +388,12 @@ def default_proxy_filter(url: httpx.URL) -> Union[None, str]:
         str: should rejetc the proxy request.
             The `str` is the reason of reject.
     """
+    host = url.host
+    if "localhost" in host:
+        return "Deny proxy for localhost."
+
     try:
-        ip_address = ipaddress.ip_address(url.host)
+        ip_address = ipaddress.ip_address(host)
     except ValueError:
         return None
 
@@ -403,7 +412,7 @@ def warn_for_none_filter(proxy_filter: None) -> ProxyFilterProto: ...
 
 
 def warn_for_none_filter(
-    proxy_filter: Union[ProxyFilterProto, None]
+    proxy_filter: Union[ProxyFilterProto, None],
 ) -> ProxyFilterProto:
     """Check whether the argument `proxy_filter` is None.
 
diff --git a/tests/test_core_lib.py b/tests/test_core_lib.py
index 5dcae0e..fe74fd9 100644
--- a/tests/test_core_lib.py
+++ b/tests/test_core_lib.py
@@ -90,10 +90,33 @@ async def _() -> JSONResponse:
 
 def test_func_default_proxy_filter() -> None:
     """Test `fastapi_proxy_lib.core._tool.default_proxy_filter()`."""
-    # 禁止访问私有IP
-    assert default_proxy_filter(httpx.URL("http://www.example.com")) is None
-    assert default_proxy_filter(httpx.URL("http://1.1.1.1")) is None
-    assert default_proxy_filter(httpx.URL("http://127.0.0.1")) is not None
+    # prevent access to private ip
+
+    def _check(url: str, should_pass: bool) -> None:
+        httpx_url = httpx.URL(url)
+        if should_pass:
+            assert default_proxy_filter(httpx_url) is None
+        else:
+            assert default_proxy_filter(httpx_url) is not None
+
+    def should_pass(url: str) -> None:
+        _check(url, True)
+
+    def should_not_pass(url: str) -> None:
+        _check(url, False)
+
+    # passed
+    should_pass("http://www.example.com")
+    should_pass("http://www.example.com/path")
+    should_pass("http://1.1.1.1")
+
+    # private ip
+    should_not_pass("http://127.0.0.1")
+    should_not_pass("http://[::1]")
+    should_not_pass("http://192.168.0.1")
+    should_not_pass("http://10.0.0.1")
+    should_not_pass("http://172.31.0.1")
+    should_not_pass("http://localhost")
 
 
 def test_non_filter_warning_for_forward_proxy() -> None: