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.

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Source ID Title
Github GHSA Github GHSA GHSA-rwrf-2pqf-9j8j Model Context Protocol Python SDK: Client fetched server-chosen $ref URLs while validating tool results against output schemas
Fixes

Solution

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Workaround

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History

Wed, 28 Oct 2026 17:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Tue, 27 Oct 2026 20:45:00 +0000

Type Values Removed Values Added
First Time appeared Modelcontextprotocol
Modelcontextprotocol python-sdk
Vendors & Products Modelcontextprotocol
Modelcontextprotocol python-sdk

Tue, 27 Oct 2026 19:30:00 +0000

Type Values Removed Values Added
Description 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.
Title Model Context Protocol Python SDK: Client fetched server-chosen $ref URLs while validating tool results against output schemas
Weaknesses CWE-918
References
Metrics cvssV3_1

{'score': 6.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H'}


Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-10-28T16:13:45.473Z

Reserved: 2026-10-26T20:00:59.830Z

Link: CVE-2026-116686

cve-icon Vulnrichment

Updated: 2026-10-28T14:34:41.665Z

cve-icon NVD

Status : Deferred

Published: 2026-10-27T20:17:13.740

Modified: 2026-10-28T17:18:03.663

Link: CVE-2026-116686

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-27T21:00:11Z

Weaknesses