CVE-2025-53366— MCP SDK Vulnerable to FastMCP Server Validation Error, Leading to Denial of Service
Quick assessment
Affected
modelcontextprotocol python-sdk
Exploitation
High exploitation probability; assess promptly
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.
Model Context Protocol Python SDK是Model Context Protocol开源的一个用于模型上下文协议服务器和客户端的开发工具。 Model Context Protocol Python SDK 1.9.4之前版本存在安全漏洞，该漏洞源于处理畸形请求时未处理异常，可能导致服务不可用。
Possible ATT&CK Techniques 1 AI
T1499 · Endpoint Denial of Service
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I. Basic Information for CVE-2025-53366
Vulnerability Information
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Vulnerability Title
MCP SDK Vulnerable to FastMCP Server Validation Error, Leading to Denial of Service
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
未捕获的异常
Source: CVE Program / CVE List V5
Vulnerability Title
Model Context Protocol Python SDK 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Model Context Protocol Python SDK是Model Context Protocol开源的一个用于模型上下文协议服务器和客户端的开发工具。 Model Context Protocol Python SDK 1.9.4之前版本存在安全漏洞，该漏洞源于处理畸形请求时未处理异常，可能导致服务不可用。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| modelcontextprotocol | python-sdk | < 1.9.4 | - |
|
II. Public POCs for CVE-2025-53366
| # | POC Description | Source Link | Shenlong Link |
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V. Comments for CVE-2025-53366
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