CVE-2025-53366 HIGH

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

Vendor Modelcontextprotocol
Product python-sdk
Weakness CWE-248
Published July 4, 2025
Last update July 8, 2025
View on NVD All CVEs

CVSS base score

8.7/10
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Confidentiality —
Integrity —

CVSS vector

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

What the vulnerability does

01Description

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.

Key dates

02Disclosure timeline

July 4, 2025 CVE published
July 8, 2025 Record updated