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

Quick assessment

Affected
modelcontextprotocol python-sdk
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Model Context Protocol（MCP）Python SDK 是用于 MCP 服务端和客户端的官方 Python 开发工具包。在 1.10.0 至 1.30.0（以及 2.2.0 之前）的版本中， 、 以及客户端工具调用在验证服务器声明的 文档时，使用了 的默认解析器。这导致未解析的 值会触发客户端从其网络环境和文件系统中获取 HTTP、HTTPS 或本地文件 URL。攻击者可利用此漏洞诱导客户端发起盲发请求或读取本地文件，且由于解析过程在事件循环中同步执行且未设置超时，攻击者还可导致所有会话停滞。该

CVSS 6.5 · Medium

Affected Version Matrix 2

VendorProduct Version RangeStatus
modelcontextprotocol python-sdk >= 1.10.0, < 1.30.0 affected
>= 2.0.0, < 2.2.0 affected
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I. Basic Information for CVE-2026-116686

Vulnerability Information
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Vulnerability Title
Model Context Protocol Python SDK: Client fetched server-chosen $ref URLs while validating tool results against output schemas
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
服务端请求伪造(SSRF)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
modelcontextprotocol python-sdk >= 1.10.0, < 1.30.0 -

II. Public POCs for CVE-2026-116686

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III. Intelligence Information for CVE-2026-116686

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Other References for CVE-2026-116686 (1)

Other References for CVE-2026-116686 (5)

Same Patch Batch · modelcontextprotocol · 2026-10-27 · 3 CVEs total

CVE-2026-116684 6.8 MEDIUM Model Context Protocol Python SDK: Server bearer-token authentication accepts tokens issue
CVE-2026-116685 5.9 MEDIUM Model Context Protocol Python SDK: HTTP client transports followed cross-origin redirects

IV. Related Vulnerabilities

Same product: python-sdk
Same vendor: modelcontextprotocol
Same weakness: CWE-918