GitHub Advisoryadvisory · PyPI
GHSA-3qhf-m339-9g5v MCP Python SDK vulnerability in the FastMCP Server causes validation error, leading to DoS
HIGH
Official page ↗
- Aliases
- CVE-2025-53366
- Ecosystem
- PyPI
- Packages
- mcp
- Severity
- High
- 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
- Weaknesses
- CWE-248
- Reviewed
- 2025-07-04
Affected packages
• PyPI mcp: < 1.9.4 → fixed in 1.9.4
Description
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.
Thank you to Rich Harang for reporting this issue.
Related
Alias · CVE (1)
- CVE-2025-53366 The MCP Python SDK, called `mcp` on PyPI, is a Python implementation of the Model Context Protocol (MCP). vulnerability
Weakness · CWE (1)
- CWE-248 Uncaught Exception weakness
References
- https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-3qhf-m339-9g5v web
- https://nvd.nist.gov/vuln/detail/CVE-2025-53366 advisory
- https://github.com/modelcontextprotocol/python-sdk/pull/822 web
- https://github.com/modelcontextprotocol/python-sdk/commit/29c69e6a47d0104d0afcea6ac35e7ab02fde809a web
- https://github.com/advisories/GHSA-3qhf-m339-9g5v advisory
- https://github.com/modelcontextprotocol/python-sdk package
- https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.9.4 web
- https://github.com/pypa/advisory-database/tree/main/vulns/mcp/PYSEC-2026-1616.yaml web
- https://pypi.org/project/mcp web