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

### 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 Python SDK: HTTP transports serve session requests without verifying the authenticated principal

### Summary In affected versions, the SSE and Streamable HTTP server transports routed incoming requests to an existing session based only on the session identifier, without verifying that the request was authenticated as the same principal that created the session. Anyone who learned or guessed a session ID could send JSON-RPC messages on that session, regardless of which bearer token the request carried. ### Am I affected? Only if a developer's application server uses an HTTP transport (SSE,

MCP Python SDK: Experimental task handlers allow any client to access and cancel other clients' tasks

### Summary In affected versions, the default request handlers installed by the experimental tasks feature (`server.experimental.enable_tasks()`) did not check which session created a task before acting on it. On a server with more than one connected client, any client could observe, read results from, and cancel tasks belonging to other clients. ### Am I affected? Only if the developer's application server calls `server.experimental.enable_tasks()`. If `grep -r enable_tasks` over their codebas

Model Context Protocol (MCP) Python SDK does not enable DNS rebinding protection by default

### Description The Model Context Protocol (MCP) Python SDK does not enable DNS rebinding protection by default for HTTP-based servers. When an HTTP-based MCP server is run on localhost without authentication using `FastMCP` with streamable HTTP or SSE transport, and has not configured `TransportSecuritySettings`, a malicious website could exploit DNS rebinding to bypass same-origin policy restrictions and send requests to the local MCP server. This could allow an attacker to invoke tools or ac

MCP Python SDK vulnerability in the FastMCP Server causes validation error, leading to DoS

A validation error in the MCP SDK can cause an unhandled exception when processing malformed requests, resulting in service unavailability (500 errors) until manually restarted. Impact may vary depending on the deployment conditions, and presence of infrastructure-level resilience measures. Thank you to Rich Harang for reporting this issue.