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CVE-2025-53366

CVE-2025-53366 · MCP SDK Vulnerable to FastMCP Server Validation Error, Leading to Denial of Service

This page contains facts from public vulnerability sources. Check the original advisory before updating.

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.

CVSS 8.7 · High · EPSS 9.8% · Fix available

Published
Updated

Stack: python

Affected products and versions

  • python-sdk

    Versions
    • < 1.9.4: Affected

    No fix published

  • mcp PyPI

    Versions
    • 0.9.1
    • 1.0.0
    • 1.1.0
    • 1.1.1
    • 1.1.2
    • 1.1.3
    • 1.2.0
    • 1.2.0rc1
    • 1.2.1
    • 1.3.0
    • 1.3.0rc1
    • 1.4.0
    • 1.4.1
    • 1.5.0
    • 1.6.0
    • 1.7.0
    • 1.7.1
    • 1.8.0
    • 1.8.1
    • 1.9.0
    • 1.9.1
    • 1.9.2
    • 1.9.3
    Affected ranges
    • ECOSYSTEM: < 1.9.4

    Update to 1.9.4

Original sources

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