dcb969fbe6 Python: pin the validated address for OpenAPI plugin requests (#14371)
### Motivation and Context

Fixes #14312.

`validate_server_url`
(`connectors/openapi_plugin/server_url_validator.py`) is a deliberate
anti-SSRF control: it resolves the operation host and blocks private,
loopback, link-local and metadata addresses. It then returned `None`,
discarding the addresses it had just vetted.

`OpenApiRunner.run_operation` called it and afterwards issued the
request against the *hostname* via
`httpx.AsyncClient(...).request(url=...)`, so httpx resolved the name a
second time when opening the connection. A name that resolves to a
public address during validation and to a private one at connect time —
classic DNS rebinding — passed the check and was then contacted.
`run_operation` attaches `auth_callback` credentials to that request.

**Severity, stated without inflation.** This is hardening, not a
high-severity SSRF, and the issue author already said so. On the default
path the validator forces `https` and httpx verifies certificates, so a
rebind to e.g. `169.254.169.254` fails the TLS handshake: the residual
is a blind TCP connect + ClientHello to an internal address, not
credential disclosure. Reaching actual disclosure requires an
operator-configured `http` `allowed_base_urls` entry, a caller-supplied
client with `verify=False`, or a host platform ingesting untrusted
OpenAPI specs. The feature is `@experimental`. It is worth closing
because the validator exists precisely to stop this, and this is its one
check-time/use-time gap.

### Description

- `validate_server_url` now returns the addresses it actually vetted, in
resolver order. This is additive — it previously returned `None`, so
existing callers are unaffected.
- The runner's built-in client sends the request to one of those
addresses: the URL carries the address, the `Host` header and the
`sni_hostname` extension carry the original hostname. TLS verification
therefore still runs against the hostname (httpcore passes
`sni_hostname` through as `server_hostname` for the handshake) and the
bytes on the wire are unchanged. `httpx.URL.copy_with(host=...)`
preserves IPv6 bracketing, the port and userinfo.
- Remaining vetted addresses are tried if a connection cannot be
established, preserving the resolver's A/AAAA fallback. Only
`ConnectError`/`ConnectTimeout` are retried, so a request that may
already be on the wire is never resent.
- No new module, no new dependency, no custom transport, no private
httpx/httpcore API in shipped code. `sni_hostname` is httpx's documented
extension for exactly this case.

Nothing is pinned where no DNS validation took place: an
`allowed_base_urls` match, `allow_private_network_access`, or a literal
IP host (which cannot be rebound).

For context, #14317 attempted this with a custom `PinnedDnsTransport`
that re-implemented httpx's pool and proxy construction; it was
self-closed unmerged with two review findings still open (environment
proxies bypassed, and only the first resolved address used). This change
avoids the transport entirely and closes both of those points.

### What this does NOT cover

- **Caller-supplied `http_client`** is not pinned. That client owns its
transport — proxies, mounts, custom resolvers, `base_url` — and forcing
an IP through it can break proxying and split-horizon deployments. Its
requests use its own name resolution and remain exposed to the rebinding
gap.
- **Environment proxies** disable pinning on the default path too. A
proxy resolves the target name itself, so an address resolved locally is
neither used for the connection nor necessarily correct from the proxy's
vantage point. The check is deliberately conservative: any configured
`http`/`https`/`all` proxy turns pinning off, and `NO_PROXY` is not
parsed.
- **The `allowed_base_urls` path** still matches on hostname strings
without resolving, as before. Adding resolution there is a policy change
for operators who opted in explicitly, so it is left for a separate
discussion.
- **Redirects are not re-validated.** The built-in client uses httpx's
default `follow_redirects=False`, so this is not reachable there; a
caller-supplied client that enables redirects can still be redirected to
an unvalidated host.

### Tests

New
`tests/unit/connectors/openapi_plugin/test_openapi_runner_dns_pinning.py`
(12 tests):

| Test | What it proves |
| --- | --- |
| `..._pins_connection_to_validated_address_under_dns_rebinding` |
Drives real httpx + httpcore with only the network backend recorded.
First resolution returns a public address, later ones return
`169.254.169.254`. Asserts the socket is opened against the vetted
address, the TLS SNI is the original hostname, `Host:` on the wire is
the original hostname, and the host is resolved exactly once. |
| `..._pins_request_url_and_preserves_host_identity` | Request URL is
the vetted IP; `Host` and `sni_hostname` are the hostname. |
| `..._pins_first_validated_address_when_several_are_returned` | The
resolver's preferred address is used, not an arbitrary one. |
| `..._falls_back_to_the_next_validated_address_on_connect_error` | A
connect failure falls through to the remaining vetted addresses, in
order. |
| `..._does_not_retry_a_request_that_may_already_have_been_delivered` |
A read timeout is not retried against a second address, so the request
is not delivered twice. |
| `..._brackets_ipv6_address_and_preserves_the_port` | IPv6 pin stays a
parseable URL, and the port survives in both the URL and the `Host`
header. |
| `..._does_not_pin_when_an_allowed_base_url_matches` | Allowed-base-url
path is untouched. |
| `..._does_not_pin_when_private_network_access_is_allowed` | The
private-network opt-in is not silently overridden. |
| `..._does_not_pin_a_literal_ip_host` | A literal address is left
exactly as it was. |
| `..._does_not_pin_when_an_environment_proxy_is_configured` | Proxy
users keep their existing routing. |
| `..._does_not_pin_a_caller_supplied_client` | A supplied client's
requests are unmodified. |
| `..._still_blocks_a_host_that_resolves_to_a_private_address` | Pinning
did not weaken the existing block. |

Plus 5 tests in `test_server_url_validator.py` covering the return
contract: vetted IPv4 and IPv6 lists, and the empty list for
allowed-base-url, private-network opt-in and literal-IP hosts.

Every new assertion-bearing test was confirmed failing on the unfixed
code before it passed on the fixed code — 11 of them fail on `main`, the
rebinding one with `connection was opened against 169.254.169.254, not
the validated address`. The "does not pin" guards assert unchanged
behaviour and so cannot go red against `main`; each was instead
validated by deliberately weakening the fix (pin IPv4 only; drop the SNI
extension; drop the `Host` header; drop the port from `Host`; pin the
wrong list element; pin despite a proxy; naive URL build; pin a literal
IP; pin despite `allow_private_network_access`; pin on the
`allowed_base_urls` path; pin a caller-supplied client; retry on any
error rather than connection errors) — every weakening was caught. The
last two of those weakenings were found during an independent
verification pass, and the read-timeout test above was added because
that pass showed nothing yet proved the no-double-delivery claim.

```
uv run pytest tests/unit/connectors/openapi_plugin/   200 passed in 5.60s
uv run ruff check semantic_kernel tests               All checks passed!   (ruff 0.9.6, the version .pre-commit-config.yaml pins)
uv run ruff format --check <changed files>            already formatted
uv run mypy semantic_kernel/connectors/openapi_plugin Success: no issues found in 22 source files
uv run pytest tests/unit                              3069 passed (baseline on pristine main 3052; +17 = exactly the new tests)
```

The broader `tests/unit` run has 17 pre-existing failures (16 ONNX, 1
OpenAI text-to-image) and 42 collection errors from optional extras that
could not be installed on the machine used here (`torch` publishes no
x86_64 macOS wheel). Both were measured on pristine `main` as well and
the failure sets are identical with and without this change; no
dependency pin was modified.

### Contribution Checklist

- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
- [x] I didn't break anyone 😄

Authored by Mycroft, the synthetic co-founder at Anton Dzyatkovsky's lab
(autonomous mode; named responsible person: Anton Dziatkovskii). The
test runs above were independently re-executed before submission.

---------

Signed-off-by: tonydzi <[email protected]>
Co-authored-by: Anton Dziatkovskii <[email protected]>
Co-authored-by: Claude Opus 5 (1M context) <[email protected]>
2026-10-05 09:56:25 +00:00
2026-08-27 17:07:35 +01:00
2023-09-04 19:55:35 +00:00
2023-02-24 16:38:23 -08:00

Semantic Kernel

Important

Semantic Kernel is now Microsoft Agent Framework! Microsoft Agent Framework (MAF) is the enterprise‑ready successor to Semantic Kernel. Microsoft Agent Framework is now available at version 1.0 as a production-ready release: stable APIs, and a commitment to long-term support. Whether you're building a single assistant or orchestrating a fleet of specialized agents, Microsoft Agent Framework 1.0 gives you enterprise-grade multi-agent orchestration, multi-provider model support, and cross-runtime interoperability via A2A and MCP.

Learn more about Semantic Kernel and Agent Framework here: Semantic Kernel and Microsoft Agent Framework on the Agent Framework blog, and try out the Semantic Kernel migration guide.

Build intelligent AI agents and multi-agent systems with this enterprise-ready orchestration framework

License: MIT Python package Nuget package Discord

What is Semantic Kernel?

Semantic Kernel is a model-agnostic SDK that empowers developers to build, orchestrate, and deploy AI agents and multi-agent systems. Whether you're building a simple chatbot or a complex multi-agent workflow, Semantic Kernel provides the tools you need with enterprise-grade reliability and flexibility.

System Requirements

  • Python: 3.10+
  • .NET: .NET 10.0+
  • Java: JDK 17+
  • OS Support: Windows, macOS, Linux

Key Features

  • Model Flexibility: Connect to any LLM with built-in support for OpenAI, Azure OpenAI, Hugging Face, NVidia and more
  • Agent Framework: Build modular AI agents with access to tools/plugins, memory, and planning capabilities
  • Multi-Agent Systems: Orchestrate complex workflows with collaborating specialist agents
  • Plugin Ecosystem: Extend with native code functions, prompt templates, OpenAPI specs, or Model Context Protocol (MCP)
  • Vector DB Support: Seamless integration with Azure AI Search, Elasticsearch, Chroma, and more
  • Multimodal Support: Process text, vision, and audio inputs
  • Local Deployment: Run with Ollama, LMStudio, or ONNX
  • Process Framework: Model complex business processes with a structured workflow approach
  • Enterprise Ready: Built for observability, security, and stable APIs

Installation

First, set the environment variable for your AI Services:

Azure OpenAI:

export AZURE_OPENAI_API_KEY=AAA....

or OpenAI directly:

export OPENAI_API_KEY=sk-...

Python

pip install semantic-kernel

.NET

dotnet add package Microsoft.SemanticKernel
dotnet add package Microsoft.SemanticKernel.Agents.Core

Java

See semantic-kernel-java build for instructions.

Quickstart

Basic Agent - Python

Create a simple assistant that responds to user prompts:

import asyncio
from semantic_kernel.agents import ChatCompletionAgent
from semantic_kernel.connectors.ai.open_ai import AzureChatCompletion

async def main():
    # Initialize a chat agent with basic instructions
    agent = ChatCompletionAgent(
        service=AzureChatCompletion(),
        name="SK-Assistant",
        instructions="You are a helpful assistant.",
    )

    # Get a response to a user message
    response = await agent.get_response(messages="Write a haiku about Semantic Kernel.")
    print(response.content)

asyncio.run(main()) 

# Output:
# Language's essence,
# Semantic threads intertwine,
# Meaning's core revealed.

Basic Agent - .NET

using Microsoft.SemanticKernel;
using Microsoft.SemanticKernel.Agents;

var builder = Kernel.CreateBuilder();
builder.AddAzureOpenAIChatCompletion(
                Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT"),
                Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT"),
                Environment.GetEnvironmentVariable("AZURE_OPENAI_API_KEY")
                );
var kernel = builder.Build();

ChatCompletionAgent agent =
    new()
    {
        Name = "SK-Agent",
        Instructions = "You are a helpful assistant.",
        Kernel = kernel,
    };

await foreach (AgentResponseItem<ChatMessageContent> response 
    in agent.InvokeAsync("Write a haiku about Semantic Kernel."))
{
    Console.WriteLine(response.Message);
}

// Output:
// Language's essence,
// Semantic threads intertwine,
// Meaning's core revealed.

Agent with Plugins - Python

Enhance your agent with custom tools (plugins) and structured output:

import asyncio
from typing import Annotated
from pydantic import BaseModel
from semantic_kernel.agents import ChatCompletionAgent
from semantic_kernel.connectors.ai.open_ai import AzureChatCompletion, OpenAIChatPromptExecutionSettings
from semantic_kernel.functions import kernel_function, KernelArguments

class MenuPlugin:
    @kernel_function(description="Provides a list of specials from the menu.")
    def get_specials(self) -> Annotated[str, "Returns the specials from the menu."]:
        return """
        Special Soup: Clam Chowder
        Special Salad: Cobb Salad
        Special Drink: Chai Tea
        """

    @kernel_function(description="Provides the price of the requested menu item.")
    def get_item_price(
        self, menu_item: Annotated[str, "The name of the menu item."]
    ) -> Annotated[str, "Returns the price of the menu item."]:
        return "$9.99"

class MenuItem(BaseModel):
    price: float
    name: str

async def main():
    # Configure structured output format
    settings = OpenAIChatPromptExecutionSettings()
    settings.response_format = MenuItem

    # Create agent with plugin and settings
    agent = ChatCompletionAgent(
        service=AzureChatCompletion(),
        name="SK-Assistant",
        instructions="You are a helpful assistant.",
        plugins=[MenuPlugin()],
        arguments=KernelArguments(settings)
    )

    response = await agent.get_response(messages="What is the price of the soup special?")
    print(response.content)

    # Output:
    # The price of the Clam Chowder, which is the soup special, is $9.99.

asyncio.run(main()) 

Agent with Plugin - .NET

using System.ComponentModel;
using Microsoft.SemanticKernel;
using Microsoft.SemanticKernel.Agents;
using Microsoft.SemanticKernel.ChatCompletion;

var builder = Kernel.CreateBuilder();
builder.AddAzureOpenAIChatCompletion(
                Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT"),
                Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT"),
                Environment.GetEnvironmentVariable("AZURE_OPENAI_API_KEY")
                );
var kernel = builder.Build();

kernel.Plugins.Add(KernelPluginFactory.CreateFromType<MenuPlugin>());

ChatCompletionAgent agent =
    new()
    {
        Name = "SK-Assistant",
        Instructions = "You are a helpful assistant.",
        Kernel = kernel,
        Arguments = new KernelArguments(new PromptExecutionSettings() { FunctionChoiceBehavior = FunctionChoiceBehavior.Auto() })

    };

await foreach (AgentResponseItem<ChatMessageContent> response 
    in agent.InvokeAsync("What is the price of the soup special?"))
{
    Console.WriteLine(response.Message);
}

sealed class MenuPlugin
{
    [KernelFunction, Description("Provides a list of specials from the menu.")]
    public string GetSpecials() =>
        """
        Special Soup: Clam Chowder
        Special Salad: Cobb Salad
        Special Drink: Chai Tea
        """;

    [KernelFunction, Description("Provides the price of the requested menu item.")]
    public string GetItemPrice(
        [Description("The name of the menu item.")]
        string menuItem) =>
        "$9.99";
}

Multi-Agent System - Python

Build a system of specialized agents that can collaborate:

import asyncio
from semantic_kernel.agents import ChatCompletionAgent, ChatHistoryAgentThread
from semantic_kernel.connectors.ai.open_ai import AzureChatCompletion, OpenAIChatCompletion

billing_agent = ChatCompletionAgent(
    service=AzureChatCompletion(), 
    name="BillingAgent", 
    instructions="You handle billing issues like charges, payment methods, cycles, fees, discrepancies, and payment failures."
)

refund_agent = ChatCompletionAgent(
    service=AzureChatCompletion(),
    name="RefundAgent",
    instructions="Assist users with refund inquiries, including eligibility, policies, processing, and status updates.",
)

triage_agent = ChatCompletionAgent(
    service=OpenAIChatCompletion(),
    name="TriageAgent",
    instructions="Evaluate user requests and forward them to BillingAgent or RefundAgent for targeted assistance."
    " Provide the full answer to the user containing any information from the agents",
    plugins=[billing_agent, refund_agent],
)

thread: ChatHistoryAgentThread = None

async def main() -> None:
    print("Welcome to the chat bot!\n  Type 'exit' to exit.\n  Try to get some billing or refund help.")
    while True:
        user_input = input("User:> ")

        if user_input.lower().strip() == "exit":
            print("\n\nExiting chat...")
            return False

        response = await triage_agent.get_response(
            messages=user_input,
            thread=thread,
        )

        if response:
            print(f"Agent :> {response}")

# Agent :> I understand that you were charged twice for your subscription last month, and I'm here to assist you with resolving this issue. Here’s what we need to do next:

# 1. **Billing Inquiry**:
#    - Please provide the email address or account number associated with your subscription, the date(s) of the charges, and the amount charged. This will allow the billing team to investigate the discrepancy in the charges.

# 2. **Refund Process**:
#    - For the refund, please confirm your subscription type and the email address associated with your account.
#    - Provide the dates and transaction IDs for the charges you believe were duplicated.

# Once we have these details, we will be able to:

# - Check your billing history for any discrepancies.
# - Confirm any duplicate charges.
# - Initiate a refund for the duplicate payment if it qualifies. The refund process usually takes 5-10 business days after approval.

# Please provide the necessary details so we can proceed with resolving this issue for you.


if __name__ == "__main__":
    asyncio.run(main())

Where to Go Next

  1. 📖 Try our Getting Started Guide or learn about Building Agents
  2. 🔌 Explore over 100 Detailed Samples
  3. 💡 Learn about core Semantic Kernel Concepts

API References

Troubleshooting

Common Issues

  • Authentication Errors: Check that your API key environment variables are correctly set
  • Model Availability: Verify your Azure OpenAI deployment or OpenAI model access

Getting Help

  • Check our GitHub issues for known problems
  • Search the Discord community for solutions
  • Include your SDK version and full error messages when asking for help

Join the community

We welcome your contributions and suggestions to the SK community! One of the easiest ways to participate is to engage in discussions in the GitHub repository. Bug reports and fixes are welcome!

For new features, components, or extensions, please open an issue and discuss with us before sending a PR. This is to avoid rejection as we might be taking the core in a different direction, but also to consider the impact on the larger ecosystem.

To learn more and get started:

Contributor Wall of Fame

semantic-kernel contributors

Code of Conduct

This project has adopted the Microsoft Open Source Code of Conduct. For more information, see the Code of Conduct FAQ or contact [email protected] with any additional questions or comments.

License

Copyright (c) Microsoft Corporation. All rights reserved.

Licensed under the MIT license.

S
Description
Integrate cutting-edge LLM technology quickly and easily into your apps
Readme MIT
482 MiB
Languages
C# 62.1%
Python 35.7%
Jupyter Notebook 1.6%
TypeScript 0.3%