CVE-2025-53366
High
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.
SeverityHigh
CVSS8.7
Exploit probability—
ProductMcp
PublishedJul 4, 2025
First seenJul 4, 2025
Weakness typeCWE-248CWE-248
How to fix
Update
- mcp1.9.4 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mcpPyPI | v < 1.9.4 | 1.9.4 |
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