MCP SDK Vulnerable to FastMCP Server Validation Error, Leading to Denial of Service
21Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 8.7epss 6.0%
exploitation probability
6.0%top 7% of all CVEs
observed exploitation
nono source reports it
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.
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
Affected products
modelcontextprotocol · python-sdk