Bug 2418445 (CVE-2025-66416) - CVE-2025-66416 mcp: DNS Rebinding Protection Disabled by Default in Model Context Protocol Python SDK
Summary: CVE-2025-66416 mcp: DNS Rebinding Protection Disabled by Default in Model Con...
Keywords:
Status: NEW
Alias: CVE-2025-66416
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
high
high
Target Milestone: ---
Assignee: Product Security DevOps Team
QA Contact:
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Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2025-12-02 19:01 UTC by OSIDB Bzimport
Modified: 2026-01-19 16:28 UTC (History)
52 users (show)

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Description OSIDB Bzimport 2025-12-02 19:01:59 UTC 
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.
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