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CVE PROGRAM SOURCE RECORD8.7 High

CVE-2025-53366

MCP SDK Vulnerable to FastMCP Server Validation Error, Leading to Denial of Service

Description

The MCP Python SDK, called `mcp` on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to version 1.9.4, a validation error in the MCP SDK can cause an unhandled exception when processing malformed requests, resulting in service unavailability (500 errors) until manually restarted. Impact may vary depending on the deployment conditions, and presence of infrastructure-level resilience measures. Version 1.9.4 contains a patch for the issue.

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

modelcontextprotocol python-sdk

  • < 1.9.4affected

References