MEDIUM 6.5 NVD
CVE-2026-116686
The Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients. From 1.10.0 until 1.30.0 and 2.2.0, ClientSessi
The Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients. From 1.10.0 until 1.30.0 and 2.2.0, ClientSession, ClientSessionGroup, and Client tool calls validate server-declared outputSchema documents with jsonschema's default resolver, causing an unresolved $ref value to fetch an HTTP, HTTPS, or file URL from the client's network and filesystem context. A server can trigger blind requests or local-file reads and can stall every session in the process because resolution runs synchronously on the event loop without a timeout. This issue is fixed in versions 1.30.0 and 2.2.0.
References
- https://github.com/modelcontextprotocol/python-sdk/commit/5ebdfed4060d8e5b11b8e2348f86bad4
- https://github.com/modelcontextprotocol/python-sdk/commit/6705402e246dc4eb1fcdf4d9902b78d3
- https://github.com/modelcontextprotocol/python-sdk/pull/3394
- https://github.com/modelcontextprotocol/python-sdk/pull/3396
- https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0
This medium severity vulnerability with a CVSS score of 6.5 was published on 2026-10-27 via NVD.
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