Is there a public exploit for CVE-2025-66416?

No public exploit for CVE-2025-66416 was found in Exploit-DB, Metasploit, Nuclei templates or public proof-of-concept repositories. That is an absence of evidence rather than proof that none exists.

How severe is CVE-2025-66416?

CVE-2025-66416 scores CVSS 7.6 (v4.0), rated high. EPSS puts the chance of exploitation in the next 30 days at 0.54%.

What does CVE-2025-66416 affect?

CVE-2025-66416 affects modelcontextprotocol mcp. It is part of the AI and agent stack (Model Context Protocol).

7.6 High

The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP).

CVE-2025-66416

Description The 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. Servers created via FastMCP() now have DNS rebinding protection enabled by default when the host parameter is 127.0.0.1 or localhost. Users are advised to update to version 1.23.0 to receive this automatic protection. Users with custom low-level server configurations using StreamableHTTPSessionManager or SseServerTransport directly should explicitly configure TransportSecuritySettings when running an unauthenticated server on…

Part of the AI stack

This affects Model Context Protocol, in MCP & tool servers.

Assessment

CVSS: 7.6 (v4.0)
Severity: High
EPSS: 0.54% chance of exploitation in the next 30 days
Known exploited: Not listed in CISA KEV
Exploit availability: Nothing found in Exploit-DB, Metasploit, Nuclei or public PoC repositories
Published: 2 December 2025
Last updated: 18 October 2026
Affected: modelcontextprotocol · python-sdk · mcp
Weakness: CWE-1188, CWE-350
Assigner: security-advisories@github.com

CVSS vectorCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

At the source

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