{"cve":"CVE-2025-66416","nvd":{"published":"2025-12-02T19:15:52.520","modified":"2026-10-18T18:10:00.100","status":"Analyzed","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_v4":{"vector":"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","score":7.6},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N","score":8.1},"cwes":["CWE-1188"],"references":["https://github.com/modelcontextprotocol/python-sdk/commit/d3a184119e4479ea6a63590bc41f01dc06e3fa99","https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-9h52-p55h-vw2f"],"products":["lfprojects:mcp_python_sdk"],"source":"nvd","synced_at":"2026-10-19T22:16:02.354564667+00:00"},"epss":{"cve":"CVE-2025-66416","score":0.00512,"percentile":0.43367,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-9h52-p55h-vw2f","url":"https://osv.dev/vulnerability/GHSA-9h52-p55h-vw2f","summary":"Model Context Protocol (MCP) Python SDK does not enable DNS rebinding protection by default","modified":"2026-09-10T03:50:31.741008234Z","packages":[{"ecosystem":"PyPI","name":"mcp","purl":"pkg:pypi/mcp","ranges":["<1.23.0"],"fixed":["1.23.0"]}]},{"id":"PYSEC-2026-1617","url":"https://osv.dev/vulnerability/PYSEC-2026-1617","summary":"Model Context Protocol (MCP) Python SDK does not enable DNS rebinding protection by default","modified":"2026-07-07T17:47:04.409703799Z","packages":[{"ecosystem":"PyPI","name":"mcp","purl":"pkg:pypi/mcp","ranges":["<1.23.0"],"fixed":["1.23.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}