CVE-2026-116686
Published:October 27, 2026
Updated:October 28, 2026
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
mcp (CONDA):
Affected version(s) >=2.0.0 <2.2.0Fix Suggestion:
Update to version 2.2.0mcp (CONDA):
Affected version(s) >=1.10.0 <1.30.0Fix Suggestion:
Update to version 1.30.0https://github.com/modelcontextprotocol/python-sdk.git (GITHUB):
Affected version(s) >=v2.0.0 <v2.2.0Fix Suggestion:
Update to version v2.2.0https://github.com/modelcontextprotocol/python-sdk.git (GITHUB):
Affected version(s) >=v1.10.0 <v1.30.0Fix Suggestion:
Update to version v1.30.0mcp (PYTHON):
Affected version(s) >=2.0.0 <2.2.0Fix Suggestion:
Update to version 2.2.0mcp (PYTHON):
Affected version(s) >=1.10.0 <1.30.0Fix Suggestion:
Update to version 1.30.0Related Resources (8)
Do you need more information?
Contact UsCVSS v4
Base Score:
7.1
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
PASSIVE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
NONE
Vulnerable System Availability
HIGH
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
6.5
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
Weakness Type (CWE)
Server-Side Request Forgery (SSRF)