CVE-2025-66416 (GCVE-0-2025-66416)

Vulnerability from cvelistv5 – Published: 2025-12-02 18:14 – Updated: 2025-12-02 18:45
VLAI
Title
DNS Rebinding Protection Disabled by Default in Model Context Protocol Python SDK for Servers Running on Localhost
Summary
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.
Severity
7.6 (High)
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
SSVC
Exploitation: none Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2025-12-02 18:42 UTC
CWE
  • CWE-1188 - Insecure Default Initialization of Resource
Assigner
GitHub_M CNA under the mitre root
CNA scorecard C 72/100 over 7951 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
modelcontextprotocol python-sdk Affected: < 1.23.0
guessed Create a notification for this product.
Show details on NVD website
To clipboard 

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