Vulnerability Description
The MCP Python SDK, called `mcp` on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to version 1.23.0, tThe Model Context Protocol (MCP) Python SDK does not enable DNS rebinding protection by default for HTTP-based servers. When an HTTP-based MCP server is run on localhost without authentication using FastMCP with streamable HTTP or SSE transport, and has not configured TransportSecuritySettings, a malicious website could exploit DNS rebinding to bypass same-origin policy restrictions and send requests to the local MCP server. This could allow an attacker to invoke tools or access resources exposed by the MCP server on behalf of the user in those limited circumstances. Note that running HTTP-based MCP servers locally without authentication is not recommended per MCP security best practices. This issue does not affect servers using stdio transport. This vulnerability is fixed in 1.23.0.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Lfprojects | Mcp Python Sdk | < 1.23.0 |
Related Weaknesses (CWE)
References
- https://github.com/modelcontextprotocol/python-sdk/commit/d3a184119e4479ea6a6359Patch
- https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-9h52Vendor Advisory
FAQ
What is CVE-2025-66416?
CVE-2025-66416 is a vulnerability with a CVSS score of 8.1 (HIGH). The MCP Python SDK, called `mcp` on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to version 1.23.0, tThe Model Context Protocol (MCP) Python SDK does not enable DNS rebi...
How severe is CVE-2025-66416?
CVE-2025-66416 has been rated HIGH with a CVSS base score of 8.1/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2025-66416?
Check the references section above for vendor advisories and patch information. Affected products include: Lfprojects Mcp Python Sdk.