Python: Harden HttpPlugin request validation (#13969)

Improve input validation and request handling in the Python HttpPlugin.

### Changes
- Add explicit opt-in for unrestricted domain access
- Tighten URL validation logic
- Improve redirect handling when domain restrictions are configured
- Add regression tests

---------

Co-authored-by: Copilot <[email protected]>

python/semantic_kernel/core_plugins/http_plugin.py

@@ -15,23 +15,48 @@ class HttpPlugin(KernelBaseModel):
     """A plugin that provides HTTP functionality.
 
     Usage:
-        kernel.add_plugin(HttpPlugin(), "http")
-
-        # With allowed domains for security:
+        # With allowed domains (recommended):
         kernel.add_plugin(HttpPlugin(allowed_domains=["example.com", "api.example.com"]), "http")
 
+        # Explicitly allow all domains (opt-in, less secure):
+        kernel.add_plugin(HttpPlugin(allow_all_domains=True), "http")
+
     Examples:
         {{http.getAsync $url}}
         {{http.postAsync $url}}
         {{http.putAsync $url}}
         {{http.deleteAsync $url}}
+
+    Security:
+        - By default, all requests are blocked unless ``allowed_domains`` is provided
+          or ``allow_all_domains`` is set to True.
+        - When ``allowed_domains`` is set and ``allow_all_domains`` is False, HTTP
+          redirects are disabled to prevent redirect-based domain bypass (SSRF).
+        - When ``allow_all_domains`` is True, redirects are allowed regardless of
+          whether ``allowed_domains`` is also set.
+        - Only ``http`` and ``https`` URL schemes are permitted.
     """
 
     allowed_domains: set[str] | None = None
-    """List of allowed domains to send requests to. If None, all domains are allowed."""
+    """Set of allowed domains to send requests to."""
+
+    allow_all_domains: bool = False
+    """When True, requests to any domain are allowed. Must be explicitly set."""
+
+    _ALLOWED_SCHEMES: frozenset[str] = frozenset({"http", "https"})
+
+    @property
+    def _allow_redirects(self) -> bool:
+        """Whether HTTP redirects should be followed.
+
+        Redirects are only allowed when ``allow_all_domains`` is True.
+        When domain restrictions are configured, redirects are disabled
+        to prevent redirect-based SSRF bypass.
+        """
+        return self.allow_all_domains
 
     def _is_uri_allowed(self, url: str) -> bool:
-        """Check if the URL's host is in the allowed domains list.
+        """Check if the URL's host and scheme are permitted.
 
         Args:
             url: The URL to check.
@@ -39,25 +64,36 @@ class HttpPlugin(KernelBaseModel):
         Returns:
             True if the URL is allowed, False otherwise.
         """
-        if self.allowed_domains is None:
-            return True
-
         parsed = urlparse(url)
-        host = parsed.hostname
-        if host is None:
+
+        # Validate scheme
+        if parsed.scheme.lower() not in self._ALLOWED_SCHEMES:
             return False
 
-        # Case-insensitive comparison
-        return host.lower() in {domain.lower() for domain in self.allowed_domains}
+        host = parsed.hostname
+        if not host:
+            return False
+
+        # If allow_all_domains is set, skip domain check
+        if self.allow_all_domains:
+            return True
+
+        # If allowed_domains is set, check against it
+        if self.allowed_domains is not None:
+            return host.lower() in {domain.lower() for domain in self.allowed_domains}
+
+        # Default: deny all
+        return False
 
     def _validate_url(self, url: str) -> None:
-        """Validate the URL, checking if it's not empty and is in the allowed domains.
+        """Validate the URL, checking scheme, emptiness, and allowed domains.
 
         Args:
             url: The URL to validate.
 
         Raises:
-            FunctionExecutionException: If the URL is empty or not in the allowed domains.
+            FunctionExecutionException: If the URL is empty, uses a disallowed scheme,
+                or targets a domain that is not allowed.
         """
         if not url:
             raise FunctionExecutionException("url cannot be `None` or empty")
@@ -77,7 +113,10 @@ class HttpPlugin(KernelBaseModel):
         """
         self._validate_url(url)
 
-        async with aiohttp.ClientSession() as session, session.get(url, raise_for_status=True) as response:
+        async with (
+            aiohttp.ClientSession() as session,
+            session.get(url, raise_for_status=True, allow_redirects=self._allow_redirects) as response,
+        ):
             return await response.text()
 
     @kernel_function(description="Makes a POST request to a uri", name="postAsync")
@@ -100,7 +139,9 @@ class HttpPlugin(KernelBaseModel):
         data = json.dumps(body) if body is not None else None
         async with (
             aiohttp.ClientSession() as session,
-            session.post(url, headers=headers, data=data, raise_for_status=True) as response,
+            session.post(
+                url, headers=headers, data=data, raise_for_status=True, allow_redirects=self._allow_redirects
+            ) as response,
         ):
             return await response.text()
 
@@ -125,7 +166,9 @@ class HttpPlugin(KernelBaseModel):
         data = json.dumps(body) if body is not None else None
         async with (
             aiohttp.ClientSession() as session,
-            session.put(url, headers=headers, data=data, raise_for_status=True) as response,
+            session.put(
+                url, headers=headers, data=data, raise_for_status=True, allow_redirects=self._allow_redirects
+            ) as response,
         ):
             return await response.text()
 
@@ -141,5 +184,8 @@ class HttpPlugin(KernelBaseModel):
         """
         self._validate_url(url)
 
-        async with aiohttp.ClientSession() as session, session.delete(url, raise_for_status=True) as response:
+        async with (
+            aiohttp.ClientSession() as session,
+            session.delete(url, raise_for_status=True, allow_redirects=self._allow_redirects) as response,
+        ):
             return await response.text()

python/tests/unit/core_plugins/test_http_plugin.py

@@ -11,7 +11,7 @@ from semantic_kernel.functions.kernel_arguments import KernelArguments
 
 
 async def test_it_can_be_instantiated():
-    plugin = HttpPlugin()
+    plugin = HttpPlugin(allow_all_domains=True)
     assert plugin is not None
 
 
@@ -23,7 +23,7 @@ async def test_it_can_be_instantiated_with_allowed_domains():
 
 async def test_it_can_be_imported():
     kernel = Kernel()
-    plugin = HttpPlugin()
+    plugin = HttpPlugin(allow_all_domains=True)
     kernel.add_plugin(plugin, "http")
     assert kernel.get_plugin(plugin_name="http") is not None
     assert kernel.get_plugin(plugin_name="http").name == "http"
@@ -36,20 +36,20 @@ async def test_get(mock_get):
     mock_get.return_value.__aenter__.return_value.text.return_value = "Hello"
     mock_get.return_value.__aenter__.return_value.status = 200
 
-    plugin = HttpPlugin()
+    plugin = HttpPlugin(allow_all_domains=True)
     response = await plugin.get("https://example.org/get")
     assert response == "Hello"
 
 
 @pytest.mark.parametrize("method", ["get", "post", "put", "delete"])
 async def test_fail_no_url(method):
-    plugin = HttpPlugin()
+    plugin = HttpPlugin(allow_all_domains=True)
     with pytest.raises(FunctionExecutionException):
         await getattr(plugin, method)(url="")
 
 
 async def test_get_none_url():
-    plugin = HttpPlugin()
+    plugin = HttpPlugin(allow_all_domains=True)
     with pytest.raises(FunctionExecutionException):
         await plugin.get(None)
 
@@ -59,7 +59,7 @@ async def test_post(mock_post):
     mock_post.return_value.__aenter__.return_value.text.return_value = "Hello World !"
     mock_post.return_value.__aenter__.return_value.status = 200
 
-    plugin = HttpPlugin()
+    plugin = HttpPlugin(allow_all_domains=True)
     arguments = KernelArguments(url="https://example.org/post", body="{message: 'Hello, world!'}")
     response = await plugin.post(**arguments)
     assert response == "Hello World !"
@@ -70,7 +70,7 @@ async def test_post_nobody(mock_post):
     mock_post.return_value.__aenter__.return_value.text.return_value = "Hello World !"
     mock_post.return_value.__aenter__.return_value.status = 200
 
-    plugin = HttpPlugin()
+    plugin = HttpPlugin(allow_all_domains=True)
     arguments = KernelArguments(url="https://example.org/post")
     response = await plugin.post(**arguments)
     assert response == "Hello World !"
@@ -81,7 +81,7 @@ async def test_put(mock_put):
     mock_put.return_value.__aenter__.return_value.text.return_value = "Hello World !"
     mock_put.return_value.__aenter__.return_value.status = 200
 
-    plugin = HttpPlugin()
+    plugin = HttpPlugin(allow_all_domains=True)
     arguments = KernelArguments(url="https://example.org/put", body="{message: 'Hello, world!'}")
     response = await plugin.put(**arguments)
     assert response == "Hello World !"
@@ -92,7 +92,7 @@ async def test_put_nobody(mock_put):
     mock_put.return_value.__aenter__.return_value.text.return_value = "Hello World !"
     mock_put.return_value.__aenter__.return_value.status = 200
 
-    plugin = HttpPlugin()
+    plugin = HttpPlugin(allow_all_domains=True)
     arguments = KernelArguments(url="https://example.org/put")
     response = await plugin.put(**arguments)
     assert response == "Hello World !"
@@ -103,7 +103,7 @@ async def test_delete(mock_delete):
     mock_delete.return_value.__aenter__.return_value.text.return_value = "Hello World !"
     mock_delete.return_value.__aenter__.return_value.status = 200
 
-    plugin = HttpPlugin()
+    plugin = HttpPlugin(allow_all_domains=True)
     arguments = KernelArguments(url="https://example.org/delete")
     response = await plugin.delete(**arguments)
     assert response == "Hello World !"
@@ -178,9 +178,9 @@ async def test_allowed_domains_case_insensitive():
     assert plugin._is_uri_allowed("https://Example.Com/path") is True
 
 
-async def test_allowed_domains_none_allows_all():
-    """Test that when allowed_domains is None, all domains are allowed."""
-    plugin = HttpPlugin()  # allowed_domains defaults to None
+async def test_allow_all_domains_allows_all():
+    """Test that when allow_all_domains is True, all domains are allowed."""
+    plugin = HttpPlugin(allow_all_domains=True)
     assert plugin._is_uri_allowed("https://any-domain.com/path") is True
     assert plugin._is_uri_allowed("https://another-domain.org/path") is True
 
@@ -214,3 +214,178 @@ async def test_allowed_domains_exact_subdomain_match():
     assert plugin._is_uri_allowed("https://sub.example.com/path") is True
     assert plugin._is_uri_allowed("https://example.com/path") is False
     assert plugin._is_uri_allowed("https://other.example.com/path") is False
+
+
+# Security regression tests
+
+
+async def test_default_constructor_denies_all():
+    """Test that default HttpPlugin() denies all requests (issue 115285)."""
+    plugin = HttpPlugin()
+    assert plugin._is_uri_allowed("https://example.com/path") is False
+    assert plugin._is_uri_allowed("https://any-domain.com/path") is False
+
+
+@pytest.mark.parametrize("method", ["get", "post", "put", "delete"])
+async def test_default_constructor_blocks_requests(method):
+    """Test that default HttpPlugin() blocks all HTTP methods (issue 115285)."""
+    plugin = HttpPlugin()
+    with pytest.raises(FunctionExecutionException, match="Sending requests to the provided location is not allowed"):
+        if method in ["post", "put"]:
+            await getattr(plugin, method)(url="https://example.com/path", body={"key": "value"})
+        else:
+            await getattr(plugin, method)(url="https://example.com/path")
+
+
+@patch("aiohttp.ClientSession.get")
+async def test_allow_all_domains_flag(mock_get):
+    """Test that allow_all_domains=True permits requests to any domain."""
+    mock_get.return_value.__aenter__.return_value.text.return_value = "OK"
+    mock_get.return_value.__aenter__.return_value.status = 200
+
+    plugin = HttpPlugin(allow_all_domains=True)
+    response = await plugin.get("https://any-domain.com/path")
+    assert response == "OK"
+
+
+@patch("aiohttp.ClientSession.get")
+async def test_redirects_disabled_with_allowed_domains(mock_get):
+    """Test that redirects are disabled when allowed_domains is set (issue 115048)."""
+    mock_get.return_value.__aenter__.return_value.text.return_value = "OK"
+    mock_get.return_value.__aenter__.return_value.status = 200
+
+    plugin = HttpPlugin(allowed_domains={"example.com"})
+    await plugin.get("https://example.com/path")
+
+    _, kwargs = mock_get.call_args
+    assert kwargs["allow_redirects"] is False
+
+
+@patch("aiohttp.ClientSession.post")
+async def test_redirects_disabled_for_post_with_allowed_domains(mock_post):
+    """Test that redirects are disabled for POST when allowed_domains is set."""
+    mock_post.return_value.__aenter__.return_value.text.return_value = "OK"
+    mock_post.return_value.__aenter__.return_value.status = 200
+
+    plugin = HttpPlugin(allowed_domains={"example.com"})
+    await plugin.post("https://example.com/path", body={"key": "value"})
+
+    _, kwargs = mock_post.call_args
+    assert kwargs["allow_redirects"] is False
+
+
+@patch("aiohttp.ClientSession.put")
+async def test_redirects_disabled_for_put_with_allowed_domains(mock_put):
+    """Test that redirects are disabled for PUT when allowed_domains is set."""
+    mock_put.return_value.__aenter__.return_value.text.return_value = "OK"
+    mock_put.return_value.__aenter__.return_value.status = 200
+
+    plugin = HttpPlugin(allowed_domains={"example.com"})
+    await plugin.put("https://example.com/path", body={"key": "value"})
+
+    _, kwargs = mock_put.call_args
+    assert kwargs["allow_redirects"] is False
+
+
+@patch("aiohttp.ClientSession.delete")
+async def test_redirects_disabled_for_delete_with_allowed_domains(mock_delete):
+    """Test that redirects are disabled for DELETE when allowed_domains is set."""
+    mock_delete.return_value.__aenter__.return_value.text.return_value = "OK"
+    mock_delete.return_value.__aenter__.return_value.status = 200
+
+    plugin = HttpPlugin(allowed_domains={"example.com"})
+    await plugin.delete("https://example.com/path")
+
+    _, kwargs = mock_delete.call_args
+    assert kwargs["allow_redirects"] is False
+
+
+@patch("aiohttp.ClientSession.get")
+async def test_redirects_allowed_with_allow_all_domains(mock_get):
+    """Test that redirects are still allowed when allow_all_domains is True."""
+    mock_get.return_value.__aenter__.return_value.text.return_value = "OK"
+    mock_get.return_value.__aenter__.return_value.status = 200
+
+    plugin = HttpPlugin(allow_all_domains=True)
+    await plugin.get("https://example.com/path")
+
+    _, kwargs = mock_get.call_args
+    assert kwargs["allow_redirects"] is True
+
+
+@patch("aiohttp.ClientSession.post")
+async def test_redirects_allowed_for_post_with_allow_all_domains(mock_post):
+    """Test that redirects are allowed for POST when allow_all_domains is True."""
+    mock_post.return_value.__aenter__.return_value.text.return_value = "OK"
+    mock_post.return_value.__aenter__.return_value.status = 200
+
+    plugin = HttpPlugin(allow_all_domains=True)
+    await plugin.post("https://example.com/path", body={"key": "value"})
+
+    _, kwargs = mock_post.call_args
+    assert kwargs["allow_redirects"] is True
+
+
+@patch("aiohttp.ClientSession.put")
+async def test_redirects_allowed_for_put_with_allow_all_domains(mock_put):
+    """Test that redirects are allowed for PUT when allow_all_domains is True."""
+    mock_put.return_value.__aenter__.return_value.text.return_value = "OK"
+    mock_put.return_value.__aenter__.return_value.status = 200
+
+    plugin = HttpPlugin(allow_all_domains=True)
+    await plugin.put("https://example.com/path", body={"key": "value"})
+
+    _, kwargs = mock_put.call_args
+    assert kwargs["allow_redirects"] is True
+
+
+@patch("aiohttp.ClientSession.delete")
+async def test_redirects_allowed_for_delete_with_allow_all_domains(mock_delete):
+    """Test that redirects are allowed for DELETE when allow_all_domains is True."""
+    mock_delete.return_value.__aenter__.return_value.text.return_value = "OK"
+    mock_delete.return_value.__aenter__.return_value.status = 200
+
+    plugin = HttpPlugin(allow_all_domains=True)
+    await plugin.delete("https://example.com/path")
+
+    _, kwargs = mock_delete.call_args
+    assert kwargs["allow_redirects"] is True
+
+
+@pytest.mark.parametrize("scheme", ["file", "ftp", "gopher", "data"])
+async def test_disallowed_schemes_blocked(scheme):
+    """Test that non-HTTP schemes are blocked."""
+    plugin = HttpPlugin(allow_all_domains=True)
+    assert plugin._is_uri_allowed(f"{scheme}://example.com/path") is False
+
+
+@pytest.mark.parametrize("scheme", ["file", "ftp", "gopher"])
+@pytest.mark.parametrize("method", ["get", "post", "put", "delete"])
+async def test_disallowed_schemes_blocked_all_methods(scheme, method):
+    """Test that non-HTTP schemes are blocked for all HTTP methods."""
+    plugin = HttpPlugin(allow_all_domains=True)
+    with pytest.raises(FunctionExecutionException, match="Sending requests to the provided location is not allowed"):
+        if method in ["post", "put"]:
+            await getattr(plugin, method)(url=f"{scheme}://example.com/path", body={"key": "value"})
+        else:
+            await getattr(plugin, method)(url=f"{scheme}://example.com/path")
+
+
+async def test_http_scheme_allowed():
+    """Test that both http and https schemes are allowed."""
+    plugin = HttpPlugin(allow_all_domains=True)
+    assert plugin._is_uri_allowed("http://example.com/path") is True
+    assert plugin._is_uri_allowed("https://example.com/path") is True
+
+
+async def test_empty_hostname_rejected():
+    """Test that URLs with empty hostnames are rejected."""
+    plugin = HttpPlugin(allow_all_domains=True)
+    assert plugin._is_uri_allowed("http://") is False
+    assert plugin._is_uri_allowed("https://") is False
+
+
+async def test_allow_all_domains_with_allowed_domains_allows_redirects():
+    """Test that redirects are allowed when both allow_all_domains and allowed_domains are set."""
+    plugin = HttpPlugin(allowed_domains={"example.com"}, allow_all_domains=True)
+    assert plugin._is_uri_allowed("https://any-domain.com/path") is True