CVE-2025-53366

Description

The MCP Python SDK, called `mcp` on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to version 1.9.4, a validation error in the MCP SDK can cause an unhandled exception when processing malformed requests, resulting in service unavailability (500 errors) until manually restarted. Impact may vary depending on the deployment conditions, and presence of infrastructure-level resilience measures. Version 1.9.4 contains a patch for the issue.

Weakness Type (CWE)

CWE-248 CWE-248

References

Other References

https://github.com/modelcontextprotocol/python-sdk/commit/29c69e6a47d0104d0afcea6ac35e7ab02fde809a https://github.com/modelcontextprotocol/python-sdk/pull/822 https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-3qhf-m339-9g5v

Frequently Asked Questions

What is CVE-2025-53366? +

The MCP Python SDK, called `mcp` on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to version 1.9.4, a validation error in the MCP SDK can cause an unhandled exception when processing malformed requests, resulting in service unavailability (500 errors) until manually restarted. Impact may vary depending on the deployment conditions, and presence of infrastructure-level resilience measures. Version 1.9.4 contains a patch for the issue.

How do I check if I'm vulnerable to CVE-2025-53366? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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