MCP Python SDK has Unhandled Exception in Streamable HTTP Transport, Leading to Denial of Service
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.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | mcp | < 1.10.0 | 1.10.0 |
References
- https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-j975-95f5-7wqh
- https://nvd.nist.gov/vuln/detail/CVE-2025-53365
- https://github.com/modelcontextprotocol/python-sdk/pull/967
- https://github.com/modelcontextprotocol/python-sdk/commit/7b420656de48cfdb90b39eb582e60b6d55c2f891
- https://github.com/modelcontextprotocol/python-sdk
- https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.10.0
- https://pypi.org/project/mcp
- https://github.com/advisories/GHSA-j975-95f5-7wqh
- https://github.com/pypa/advisory-database/tree/main/vulns/mcp/PYSEC-2026-1618.yaml
- 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- Weakness (CWE)
CWE-248- Platform
- Python (PyPI)
- Package
mcp- Disclosed
- 04.07.2025
- Updated
- 11.10.2026 14:18
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-1618 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-j975-95f5-7wqh - CC BY 4.0
Vulnerability history: mcp
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 6
- First → latest
- 07.2025 07.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 6
Disclosures per year
- 2025: 3
- 2026: 3
-
MCP Python SDK has Unhandled Exception in Streamable HTTP Transport, Leading to Denial of Service this entry
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