Python: Default MCP SSE server samples to loopback with host validation#14127
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SergeyMenshykh merged 3 commits intoJun 30, 2026
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Update the MCP SSE server demos to bind to 127.0.0.1 by default with a new --host opt-in, add Starlette TrustedHost and Origin allowlist middleware for loopback callers, and document the behavior in the README. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Pull request overview
Updates the Python MCP SSE demo servers to be safer-by-default for local development by binding to loopback, adding Host/Origin validation, and reducing debug verbosity so the samples don’t accidentally ship insecure defaults.
Changes:
- Add
--host(default127.0.0.1) and warn when binding beyond loopback. - Add
TrustedHostMiddlewareplus an Origin allowlist middleware to reduce DNS-rebinding risk. - Turn off Starlette debug mode for SSE demos and document the new behavior in the sample README.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.
| File | Description |
|---|---|
| python/samples/demos/mcp_server/sk_mcp_server.py | Adds loopback default binding, Host/Origin validation middleware, and disables Starlette debug for SSE. |
| python/samples/demos/mcp_server/agent_as_server.py | Mirrors the SSE loopback default binding and Host/Origin validation changes for the agent-based MCP server demo. |
| python/samples/demos/mcp_server/README.md | Documents loopback-by-default SSE behavior, --host opt-in, and points to mcp_with_oauth for production patterns. |
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Fail fast when --transport sse is used without --port, treat undecodable Origin headers as forbidden instead of erroring, and use ipaddress loopback detection (incl. IPv6 ::1) for the non-loopback bind warning. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
eavanvalkenburg
approved these changes
Jun 30, 2026
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
TaoChenOSU
approved these changes
Jun 30, 2026
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Motivation and Context
The Python MCP server demos under
python/samples/demos/mcp_server/can optionally run over the SSE transport (--transport sse). This updates that sample wiring to follow the Model Context Protocol guidance for local development servers, so developers who use these demos as a starting point inherit sensible defaults.Description
127.0.0.1instead of0.0.0.0. A new--hostargument makes binding to other interfaces an explicit opt-in that logs a warning.TrustedHostMiddlewareplus a small Origin allowlist middleware so the local listener only serves loopback callers (requests without anOriginheader are still allowed, for non-browser MCP clients).Starlette(debug=True)todebug=Falseso the demos don't ship verbose debug output.--hostopt-in, and points to the existingmcp_with_oauthsample for authenticated, network-reachable deployments.Applies to
sk_mcp_server.pyandagent_as_server.py. The stdio transport (the default) and the other stdio-only samples are unchanged.Contribution Checklist