CVE-2025-53366 - CVE House
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Status published High CVE-2025-53366

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

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.

Impact Analysis

Refer to official advisory for detailed impact metrics.

Remediation

Ensure systems are updated to the latest vendor-supplied patch levels.

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Credits & Attribution

No credits recorded in the NVD database.

References

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Affected Vendor

modelcontextprotocol

View all reports →

Affected Software

python-sdk
Vulnerable Versions:
< 1.9.4

Timeline

Official Publish: July 4th, 2025
Last Modified: July 8th, 2025
Added to House: July 22nd, 2026

CVSS Vectors

Weaknesses (CWE)

CWE-248

MITRE ATT&CK TTPs

T1190 Exploit Public-Facing Application
Initial Access
T1203 Exploitation for Client Execution
Execution
T1213 Data from Information Repositories
Collection
T1499.003 Application Exhaustion Flood
Impact