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CVE-2026-116686

CVE-2026-116686 · Model Context Protocol Python SDK: Client fetched server-chosen $ref URLs while validating tool results against output schemas

This page contains facts from public vulnerability sources. Check the original advisory before updating.

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.

CVSS 6.5 · Medium · EPSS 0.3% · Fix available

Published
Updated

Stack: python

Affected products and versions

  • python-sdk

    Versions
    • >= 1.10.0, < 1.30.0: Affected
    • >= 2.0.0, < 2.2.0: Affected

    No fix published

  • mcp PyPI

    Versions
    • 2.0.0
    • 2.0.1
    • 2.1.0
    • 2.1.1
    Affected ranges
    • ECOSYSTEM: ≥ 2.0.0, < 2.2.0

    Update to 2.2.0

  • mcp PyPI

    Versions
    • 1.10.0
    • 1.10.1
    • 1.11.0
    • 1.12.0
    • 1.12.1
    • 1.12.2
    • 1.12.3
    • 1.12.4
    • 1.13.0
    • 1.13.1
    • 1.14.0
    • 1.14.1
    • 1.15.0
    • 1.16.0
    • 1.17.0
    • 1.18.0
    • 1.19.0
    • 1.20.0
    • 1.21.0
    • 1.21.1
    • 1.21.2
    • 1.22.0
    • 1.23.0
    • 1.23.1
    • 1.23.2
    • 1.23.3
    • 1.24.0
    • 1.25.0
    • 1.26.0
    • 1.27.0
    • 1.27.1
    • 1.27.2
    • 1.28.0
    • 1.28.1
    • 1.29.0
    • 1.29.1
    Affected ranges
    • ECOSYSTEM: ≥ 1.10.0, < 1.30.0

    Update to 1.30.0

Original sources

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