CVSS 4.0
8.7 highCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:NCVE-2025-53366
High (8.7). EPSS 9.8% chance of exploitation in the next 30 days. Fixed in mcp 1.9.4.
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.
Severity
- EPSS
- 9.8% chance of exploitation in the next 30 days; higher than 95% of CVEs (scores of 2026-10-31)
- CWE
- CWE-248
- Published
- Modified
- Record from
- the NVD, synced
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-3qhf-m339-9g5v | PyPI | mcp | <1.9.4 | 1.9.4 |
| PYSEC-2026-1616 | PyPI | mcp | <1.9.4 | 1.9.4 |