Validation Error in MCP Python SDK Causing Service Disruption
CVE-2025-53366

8.7HIGH

Key Information:

Vendor

Modelcontextprotocol

Status
Python-sdk
Vendor
CVE Published:
4 July 2025

What is CVE-2025-53366?

The MCP Python SDK, available on PyPI, is vulnerable to a validation error that leads to unhandled exceptions when processing malformed requests. This can result in service disruptions characterized by 500 errors, requiring manual intervention to restart the service. The impact of this vulnerability is contingent upon the specific deployment and the existence of infrastructure-level resilience measures. Users are advised to update to version 1.9.4, which includes a corrective patch for this issue.

Affected Version(s)

python-sdk < 1.9.4

References

https://github.com/modelcontextprotocol/python-sdk/securi...
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https://github.com/modelcontextprotocol/python-sdk/pull/822
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https://github.com/modelcontextprotocol/python-sdk/commit...
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CVSS V4

Score:
8.7
Severity:
HIGH
Confidentiality:
None
Integrity:
None
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

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CVE-2025-53366 : Validation Error in MCP Python SDK Causing Service Disruption