—

PYSEC-2026-1618

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

Details

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.

Are you affected?

Enter the version of the package you're using.

Affected packages

PyPI / mcp

Introduced in: 0 Fixed in: 1.10.0

Fix pip install --upgrade 'mcp>=1.10.0'

References

https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-j975-95f5-7wqh [WEB]
https://nvd.nist.gov/vuln/detail/CVE-2025-53365 [ADVISORY]
https://github.com/modelcontextprotocol/python-sdk/pull/967 [WEB]
https://github.com/modelcontextprotocol/python-sdk/commit/7b420656de48cfdb90b39eb582e60b6d55c2f891 [WEB]
https://github.com/modelcontextprotocol/python-sdk [PACKAGE]
https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.10.0 [WEB]
https://pypi.org/project/mcp [PACKAGE]
https://github.com/advisories/GHSA-j975-95f5-7wqh [ADVISORY]