CVE-2025-53366

HIGH

mcp < 1.9.4 - Denial of Service via Malformed Request Validation Error

Title source: llm
STIX 2.1

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.

References (3)

Core 3

Scores

CVSS v4 8.7
EPSS 0.0569
EPSS Percentile 92.0%
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

CISA SSVC

Vulnrichment
Exploitation none
Automatable yes
Technical Impact partial

Details

CWE
CWE-248
Status published
Products (2)
modelcontextprotocol/python-sdk < 1.9.4
pypi/mcp 0 - 1.9.4PyPI
Published Jul 04, 2025
Tracked Since Feb 18, 2026