CVE-2026-59950: MCP Python SDK: WebSocket server transport does not support Host/Origin validation
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.
References
- github.com/advisories/GHSA-vj7q-gjh5-988w
- github.com/modelcontextprotocol/python-sdk/commit/777b8d06710c140e3606b0d4598e2aa48546c266
- github.com/modelcontextprotocol/python-sdk/pull/2992
- github.com/modelcontextprotocol/python-sdk/releases/tag/v1.28.1
- github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-vj7q-gjh5-988w
- nvd.nist.gov/vuln/detail/CVE-2026-59950
Code Behaviors & Features
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