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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-116686
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-27 20:17:13 UTC
Updated2026-10-27 20:17:13 UTC
DescriptionThe 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.

Risk And Classification

Primary CVSS: v3.1 6.5 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Problem Types: CWE-918 | CWE-918 CWE-918: Server-Side Request Forgery (SSRF)

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
3.1CNADECLARED6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Modelcontextprotocol Python-sdk affected >= 1.10.0, < 1.30.0 Not specified
CNA Modelcontextprotocol Python-sdk affected >= 2.0.0, < 2.2.0 Not specified

References

ReferenceSourceLinkTags
github.com/modelcontextprotocol/python-sdk/pull/3396 [email protected] github.com
github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0 [email protected] github.com
github.com/modelcontextprotocol/python-sdk/commit/6705402e246dc4eb1fcdf4... [email protected] github.com
github.com/modelcontextprotocol/python-sdk/pull/3394 [email protected] github.com
github.com/modelcontextprotocol/python-sdk/commit/5ebdfed4060d8e5b11b8e2... [email protected] github.com
github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-rwrf... [email protected] github.com
github.com/modelcontextprotocol/python-sdk/releases/tag/v2.2.0 [email protected] github.com
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