MCP Python SDK has Unhandled Exception in Streamable HTTP Transport, Leading to Denial of Service

ALTO 8.7CVE-2025-53365 · GHSA-j975-95f5-7wqh · PYSEC-2026-1618 · Published 04/07/2025 · updated 17/06/2026

Package	Affected versions	Patched versions
mcp PyPI	`< 1.10.0`	`1.10.0`

Description

If a client deliberately triggers an exception after establishing a streamable HTTP session, this can lead to an uncaught ClosedResourceError on the server side, causing the server to crash and requiring a restart to restore service. Impact may vary depending on the deployment conditions, and presence of infrastructure-level resilience measures.

Thank you to Rich Harang for reporting this issue.

NVD description

The MCP Python SDK, called `mcp` on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to version 1.10.0, if a client deliberately triggers an exception after establishing a streamable HTTP session, this can lead to an uncaught ClosedResourceError on the server side, causing the server to crash and requiring a restart to restore service. Impact may vary depending on the deployment conditions, and presence of infrastructure-level resilience measures. Version 1.10.0 contains a patch for the issue.

References

modelcontextprotocol/python-sdk security advisory · WEB
nvd.nist.gov/vuln/detail/CVE-2025-53365 · ADVISORY
modelcontextprotocol/python-sdk#967 · WEB
modelcontextprotocol/python-sdk commit 7b42065 · WEB
GitHub Advisory GHSA-j975-95f5-7wqh · ADVISORY
modelcontextprotocol/python-sdk · PACKAGE
modelcontextprotocol/python-sdk release v1.10.0 · WEB
pypa/advisory-database · WEB
pypi.org/project/mcp · WEB

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Package

Affected versions

Patched versions

mcp

PyPI

< 1.10.0

1.10.0

Description

Thank you to Rich Harang for reporting this issue.

NVD description