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[ CVE-2026-116685 · Published 27 Oct 2026 ]

Model Context Protocol Python SDK: HTTP client transports followed cross-origin redirects carrying custom headers and bodies

CVSS 5.9 EPSS <1%Fix available

[ Description ]Official description

The Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients. From 1.8.0 until 1.30.0 and 2.2.0, streamable_http_client, streamablehttp_client, sse_client, ClientSessionGroup, OAuth, and create_mcp_http_client client paths enable follow_redirects and follow redirects to a different origin, forwarding caller-supplied custom credential headers and, for 307 or 308 responses, the request body. An attacker who can influence a trusted endpoint's redirect destination can receive that material. This issue is fixed in versions 1.30.0 and 2.2.0.

[ Fixes ]Fixes and patches

  • mcp 2.2.0Fixed version · GitHub Advisories · pip package mcp: upgrade to 2.2.0 or later (affected >= 2.0.0, < 2.2.0)
  • mcp 1.30.0Fixed version · GitHub Advisories · pip package mcp: upgrade to 1.30.0 or later (affected >= 1.8.0, < 1.30.0)

[ Packages ]Affected open-source packages

[ References ]References