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Vulnerability · Published Oct 27, 2026 · Assigned by GitHub_M

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

Medium 6.5

In plain English

A medium-severity server-side request forgery in python-sdk from modelcontextprotocol. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 27% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)6.5Medium
Exploit odds (30 days)0.3%top 72.8% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
PyPImcp2.2.0GHSA-rwrf-2pqf-9j8j
PyPImcp1.30.0GHSA-rwrf-2pqf-9j8j

Affected products (as reported)

VendorProductVersions
modelcontextprotocol python-sdk >= 1.10.0, < 1.30.0>= 2.0.0, < 2.2.0

Weakness: CWE-918 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

References