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.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Privileges Required
None
No privileges needed
User Interaction
Required
User action required
Impact Assessment
Confidentiality
None
No data leak
Integrity
None
No data modification
Availability
High
Complete denial of service
CVSS Vector v3.1
Weakness Type (CWE)
Vulnerable Products
modelcontextprotocol:python-sdk
References 7
https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-rwr…
https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-rwrf-2pqf-9j8j
https://github.com/modelcontextprotocol/python-sdk/pull/3394
https://github.com/modelcontextprotocol/python-sdk/pull/3394
https://github.com/modelcontextprotocol/python-sdk/pull/3396
https://github.com/modelcontextprotocol/python-sdk/pull/3396
https://github.com/modelcontextprotocol/python-sdk/commit/5ebdfed4060d8e5b11b8e…
https://github.com/modelcontextprotocol/python-sdk/commit/5ebdfed4060d8e5b11b8e2348f86bad4d1fb8836
https://github.com/modelcontextprotocol/python-sdk/commit/6705402e246dc4eb1fcdf…
https://github.com/modelcontextprotocol/python-sdk/commit/6705402e246dc4eb1fcdf4d9902b78d3c9c36e1b
https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0
https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0
https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.2.0
https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.2.0