The MCP Python SDK, called `mcp` on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to version 1.23.0, tThe 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 access resources exposed by the MCP server on behalf of the user in those limited circumstances. Note that running HTTP-based MCP servers locally without authentication is not recommended per MCP security best practices. This issue does not affect servers using stdio transport. This vulnerability is fixed in 1.23.0.
Fix
Patch, vendor advisory and mitigation references on NVD 2
- https://github.com/modelcontextprotocol/python-sdk/commit/d3a184119e4479ea6a63590bc41f01dc06e3fa99 Patch
- https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-9h52-p55h-vw2f Vendor Advisory
Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.
Change history 1
- First seenCVSS 7.6 · lfprojectsNVD modified 2026-10-18 18:10
Affected (CPE criteria) 1
cpe:2.3:a:lfprojects:mcp_python_sdk:*:*:*:*:*:*:*:*