chore(deps): update dependency mcp to v1.28.1 [security]

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
mcp	1.27.2 → 1.28.1

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MCP Python SDK: WebSocket server transport does not support Host/Origin validation

CVE-2026-59950 / GHSA-vj7q-gjh5-988w

More information

Details

Summary

In affected versions, the deprecated WebSocket server transport (mcp.server.websocket.websocket_server) accepted the WebSocket handshake without applying any Host or Origin header validation. The TransportSecuritySettings mechanism that the SSE and Streamable HTTP transports use for this purpose was not wired into the WebSocket transport, so there was no SDK-level way to restrict which origins could connect.

Am I affected?

Only if a developer's application server exposes mcp.server.websocket.websocket_server. This transport has never been part of the MCP specification, is marked deprecated, and is not reachable through FastMCP — a developer must have wired it into an ASGI application themselves. Servers using stdio, SSE, or Streamable HTTP are not affected by this advisory.

Details

websocket_server() constructed a Starlette WebSocket and called accept(subprotocol="mcp") immediately, with no inspection of the connection's headers. By contrast, SseServerTransport and StreamableHTTPServerTransport accept an optional security_settings: TransportSecuritySettings and run TransportSecurityMiddleware.validate_request() against the incoming Host and Origin headers before establishing a session. Because browsers attach an Origin header to cross-origin WebSocket upgrade requests but do not enforce a same-origin policy on the response, a web page served from any origin could open a WebSocket to a reachable MCP server on this transport, complete the initialize handshake, and issue JSON-RPC requests on the resulting session.

Impact

A user who runs an MCP server on this transport bound to localhost or a LAN address, without a separate authentication or origin gate in front of it, and visits a malicious web page, can have that page enumerate and invoke the server's tools and read its resources. The consequences depend entirely on what the server exposes. The transport itself requires no token or prior session. Some browsers prompt before allowing a public page to open a connection to a local-network address, which adds a user-interaction step but is not a substitute for server-side validation.

Mitigation

Upgrade to version 1.28.1 or later, in which websocket_server() accepts the same optional security_settings: TransportSecuritySettings argument as the other HTTP-based transports and validates the Host and Origin headers before accepting the handshake; a request that fails validation is rejected with HTTP 403 and ValueError("Request validation failed") is raised to the caller. As with the other transports the parameter defaults to None, which leaves validation disabled, so upgrading alone does not change behaviour: pass a TransportSecuritySettings with enable_dns_rebinding_protection=True and appropriate allowed_hosts / allowed_origins to receive the protection. The recommended path remains to migrate off this deprecated transport to Streamable HTTP, where FastMCP enables this protection automatically for localhost binds. The WebSocket transport has been removed entirely in v2.

Severity

• CVSS Score: 7.6 / 10 (High)
• Vector String: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

References

• https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-vj7q-gjh5-988w
• https://nvd.nist.gov/vuln/detail/CVE-2026-59950
• https://github.com/modelcontextprotocol/python-sdk/pull/2992
• https://github.com/modelcontextprotocol/python-sdk/commit/777b8d06710c140e3606b0d4598e2aa48546c266
• https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.28.1
• https://github.com/advisories/GHSA-vj7q-gjh5-988w

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

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Release Notes

modelcontextprotocol/python-sdk (mcp)

v1.28.1

Compare Source

What's Changed

• [v1.x] Buffer per-request StreamableHTTP streams; store priming event before dispatch by @​maxisbey in #​2948
• [v1.x] Set Development Status classifier to Production/Stable by @​maxisbey in #​2976
• [v1.x] Support TransportSecuritySettings in the WebSocket server transport by @​maxisbey in #​2992

Full Changelog: modelcontextprotocol/python-sdk@v1.28.0...v1.28.1

v1.28.0

Compare Source

Deprecations

Two API surfaces now emit DeprecationWarning ahead of their removal in v2. Nothing is removed in 1.x, and the warnings fire only when the deprecated API is called - importing the modules stays silent.

• WebSocket transport - mcp.client.websocket.websocket_client and mcp.server.websocket.websocket_server. WebSocket was never part of the MCP specification; use the streamable HTTP transport instead. The TypeScript SDK has likewise removed its WebSocket client for v2 (modelcontextprotocol/typescript-sdk#1783).
• Experimental tasks API - ClientSession.experimental, Server.experimental, ServerSession.experimental, and the experimental_task_handlers= kwarg on ClientSession. Tasks (SEP-1686) were removed from the MCP specification and are expected to return as a separate MCP extension.

If your test suite runs with filterwarnings = ["error"] and exercises these paths, add a scoped ignore such as ignore:The experimental tasks API is deprecated:DeprecationWarning or ignore:The WebSocket .* transport is deprecated:DeprecationWarning.

See #​2828 for full details.

What's Changed

• [v1.x] Support Python 3.14 by @​maxisbey in #​2769
• fix: omit null optional fields from task result payloads by @​liuzemei in #​2809
• [v1.x] Deprecate the WebSocket transport and the experimental tasks entry points by @​maxisbey in #​2828
• [v1.x] Add a v2 status banner to the README by @​maxisbey in #​2835
• [v1.x] Deflake the child process cleanup tests by @​maxisbey in #​2839

New Contributors

• @​liuzemei made their first contribution in #​2809

Full Changelog: modelcontextprotocol/python-sdk@v1.27.2...v1.28.0

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