DNS Rebinding Vulnerability in MCP Python SDK by Model Context Protocol

CVE-2025-66416

What is CVE-2025-66416?

The MCP Python SDK, which implements the Model Context Protocol, poses a security risk due to the lack of default DNS rebinding protection for HTTP-based servers prior to version 1.23.0. If an MCP server runs without authentication on localhost using FastMCP with streamable HTTP or SSE transport, attackers could exploit this gap. Malicious websites may leverage DNS rebinding to circumvent same-origin policy safeguards, potentially allowing them to execute unauthorized requests on the local MCP server. This vulnerability highlights the importance of securing local servers and adhering to best security practices when using the MCP SDK.

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