From f047d04882e145928f1cfe73c04b5872e241b3bd Mon Sep 17 00:00:00 2001
From: Franck Nijhof <git@frenck.dev>
Date: Thu, 14 Jan 2021 20:02:01 +0100
Subject: [PATCH] Add filtering

---
 homeassistant/components/http/__init__.py     |  6 +-
 .../components/http/security_filter.py        | 51 ++++++++++++++++
 tests/components/http/test_security_filter.py | 58 +++++++++++++++++++
 3 files changed, 114 insertions(+), 1 deletion(-)
 create mode 100644 homeassistant/components/http/security_filter.py
 create mode 100644 tests/components/http/test_security_filter.py

diff --git a/homeassistant/components/http/__init__.py b/homeassistant/components/http/__init__.py
index 9e47dd29a23..7f70d49f686 100644
--- a/homeassistant/components/http/__init__.py
+++ b/homeassistant/components/http/__init__.py
@@ -30,6 +30,7 @@ from .const import KEY_AUTHENTICATED, KEY_HASS, KEY_HASS_USER  # noqa: F401
 from .cors import setup_cors
 from .forwarded import async_setup_forwarded
 from .request_context import setup_request_context
+from .security_filter import setup_security_filter
 from .static import CACHE_HEADERS, CachingStaticResource
 from .view import HomeAssistantView  # noqa: F401
 from .web_runner import HomeAssistantTCPSite
@@ -296,7 +297,10 @@ class HomeAssistantHTTP:
         )
         app[KEY_HASS] = hass
 
-        # Order matters, forwarded middleware needs to go first.
+        # Order matters, security filters middle ware needs to go first,
+        # forwarded middleware needs to go second.
+        setup_security_filter(app)
+
         # Only register middleware if `use_x_forwarded_for` is enabled
         # and trusted proxies are provided
         if use_x_forwarded_for and trusted_proxies:
diff --git a/homeassistant/components/http/security_filter.py b/homeassistant/components/http/security_filter.py
new file mode 100644
index 00000000000..32ebcacfff4
--- /dev/null
+++ b/homeassistant/components/http/security_filter.py
@@ -0,0 +1,51 @@
+"""Middleware to add some basic security filtering to requests."""
+import logging
+import re
+
+from aiohttp.web import HTTPBadRequest, middleware
+
+from homeassistant.core import callback
+
+_LOGGER = logging.getLogger(__name__)
+
+# mypy: allow-untyped-defs
+
+# fmt: off
+FILTERS = re.compile(
+    r"(?:"
+
+    # Common exploits
+    r"proc/self/environ"
+    r"|(<|%3C).*script.*(>|%3E)"
+
+    # File Injections
+    r"|(\.\.//?)+"  # ../../anywhere
+    r"|[a-zA-Z0-9_]=/([a-z0-9_.]//?)+"  # .html?v=/.//test
+
+    # SQL Injections
+    r"|union.*select.*\("
+    r"|union.*all.*select.*"
+    r"|concat.*\("
+
+    r")",
+    flags=re.IGNORECASE,
+)
+# fmt: on
+
+
+@callback
+def setup_security_filter(app):
+    """Create security filter middleware for the app."""
+
+    @middleware
+    async def security_filter_middleware(request, handler):
+        """Process request and block commonly known exploit attempts."""
+        if FILTERS.search(request.raw_path):
+            _LOGGER.warning(
+                "Filtered a potential harmful request to: %s", request.raw_path
+            )
+            raise HTTPBadRequest
+
+        return await handler(request)
+
+    app.middlewares.append(security_filter_middleware)
diff --git a/tests/components/http/test_security_filter.py b/tests/components/http/test_security_filter.py
new file mode 100644
index 00000000000..8190c514603
--- /dev/null
+++ b/tests/components/http/test_security_filter.py
@@ -0,0 +1,58 @@
+"""Test security filter middleware."""
+from aiohttp import web
+import pytest
+
+from homeassistant.components.http.security_filter import setup_security_filter
+
+
+async def mock_handler(request):
+    """Return OK."""
+    return web.Response(text="OK")
+
+
+@pytest.mark.parametrize(
+    "request_path,request_params",
+    [
+        ("/", {}),
+        ("/lovelace/dashboard", {}),
+        ("/frontend_latest/chunk.4c9e2d8dc10f77b885b0.js", {}),
+        ("/static/translations/en-f96a262a5a6eede29234dc45dc63abf2.json", {}),
+        ("/", {"test": "123"}),
+    ],
+)
+async def test_ok_requests(request_path, request_params, aiohttp_client):
+    """Test request paths that should not be filtered."""
+    app = web.Application()
+    app.router.add_get("/{all:.*}", mock_handler)
+
+    setup_security_filter(app)
+
+    mock_api_client = await aiohttp_client(app)
+    resp = await mock_api_client.get(request_path, params=request_params)
+
+    assert resp.status == 200
+    assert await resp.text() == "OK"
+
+
+@pytest.mark.parametrize(
+    "request_path,request_params",
+    [
+        ("/proc/self/environ", {}),
+        ("/", {"test": "/test/../../api"}),
+        ("/", {"test": "test/../../api"}),
+        ("/", {"sql": ";UNION SELECT (a, b"}),
+        ("/", {"sql": "concat(..."}),
+        ("/", {"xss": "<script >"}),
+    ],
+)
+async def test_bad_requests(request_path, request_params, aiohttp_client):
+    """Test request paths that should be filtered."""
+    app = web.Application()
+    app.router.add_get("/{all:.*}", mock_handler)
+
+    setup_security_filter(app)
+
+    mock_api_client = await aiohttp_client(app)
+    resp = await mock_api_client.get(request_path, params=request_params)
+
+    assert resp.status == 400