GCD AI RADAR
incidents/AIR-2025-0305

CVE-2025-53366: MCP Python SDK FastMCP Server Denial of Service Vulnerability

Attack on AI2 Disclosed vulnerabilityInfrastructure vulnerability

A validation error within the FastMCP server component triggers unhandled exceptions upon processing malformed requests. This results in repeated server errors and service unavailability until restarted.

disclosed CVENo confirmed exploitation, so this record is tracked as a disclosed vulnerability and not counted as an incident. It moves into the counts if CISA or the vendor confirms exploitation. Why

Details

type
Attack on AI
An AI model, agent or AI-powered product was the thing exploited, abused or leaked.
categories
  • Infrastructure vulnerability
    CVEs and advisories in AI frameworks, inference servers, MCP servers, AI developer tools and hosting stacks.
owasp llm top 10
mitre atlas
no technique for these categories
Both rows are derived from the type and categories (OWASP 2025 edition, ATLAS release 2026.09), not classified per record. How
severity
2 · Disclosed vulnerability
CVE or vendor advisory, patched or patchable, no confirmed exploitation.
targets
Framework / tooling
products
mcp, fastmcp server
incident date
4 Jul 2025
first reported
4 Jul 2025
origin
GitHub Advisory Database
Vulnerability record from NVD / the GitHub Advisory Database. This product uses the NVD API but is not endorsed or certified by the NVD.
classifier confidence
0.95 · published at or above 0.80; see the methodology
tags
CVE-2025-53366 · mcp · dos
record
created 2026-10-18 07:00Z · updated 2026-10-18 10:04Z · json

Sources · 2

  1. 2025-07-04
    CVE-2025-53366: MCP Python SDK vulnerability in the FastMCP Server causes validation error, leading to DoS
    GitHub Advisory Database · github.com/advisories/GHSA-3qhf-m339-9g5v
  2. 2025-07-04
    CVE-2025-53366: The MCP Python SDK, called `mcp` on PyPI, is a Python implementation of the Model Context Protocol (MCP).
    NVD · nvd.nist.gov/vuln/detail/CVE-2025-53366

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