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AI agent vulnerability · MCP Python SDK

CVE-2025-53365: MCP Python SDK has Unhandled Exception in Streamable HTTP Transport, Leading to Denial of Service

highCVSS 4.0 8.7GHSA-j975-95f5-7wqh

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.

Published Jul 4, 2025 · Updated Jul 16, 2026

Affected packages

mcp

Ecosystem
PyPI
Affected
< 1.10.0
Fixed in
1.10.0
Check
pip show mcp

Advisory details

From the GitHub Advisory Database (CC BY 4.0).

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.

Thank you to Rich Harang for reporting this issue.

Credited to rharang.

References

How this page is made: the data panel comes from the GitHub Advisory Database, CISA’s KEV catalog, the NVD and FIRST EPSS, and updates twice a day. No analysis has been written for this entry yet. Methodology

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