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archive/Patch now/AIR-2025-0383
closedclosed 2 Dec 2025Patch now2 Disclosed vulnerabilityAI

CVE-2025-66416: MCP Python SDK lacks default DNS rebinding protection

Model Context Protocol Python SDK

The Model Context Protocol Python SDK fails to enable DNS rebinding protection by default for HTTP servers. Attackers could exploit this via malicious websites to access local MCP resources.

disclosed CVENo confirmed exploitation, so this record is tracked as a disclosed vulnerability and not counted as an incident. It moves into the counts if CISA or the vendor confirms exploitation. Why

CVSS
7.6
EPSS
0.01 · top 54% · 2026-11-13
EPSS scores by FIRST
fix status
Fix status unknown
first report
2 Dec 2025
last update
26 Dec 2025
CVE ids
CVE-2025-66416other records

Timeline · 3

  1. 2 Dec 2025CVE-2025-66416: Model Context Protocol (MCP) Python SDK does not enable DNS rebinding protection by default
  2. 2 Dec 2025CVE-2025-66416: The MCP Python SDK, called `mcp` on PyPI, is a Python implementation of the Model Context Protocol (MCP).
  3. 26 Dec 2025GHSA-rcfx-77hg-w2wv: FastMCP updated to MCP 1.23+ due to CVE-2025-66416

Sources · 3

Advisories and databases

  1. 2025-12-02
    CVE-2025-66416: Model Context Protocol (MCP) Python SDK does not enable DNS rebinding protection by default
    GitHub Advisory Database · github.com/advisories/GHSA-9h52-p55h-vw2f
  2. 2025-12-02
    CVE-2025-66416: The MCP Python SDK, called `mcp` on PyPI, is a Python implementation of the Model Context Protocol (MCP).
    NVD · nvd.nist.gov/vuln/detail/CVE-2025-66416
  3. 2025-12-26
    GHSA-rcfx-77hg-w2wv: FastMCP updated to MCP 1.23+ due to CVE-2025-66416
    GitHub Advisory Database · github.com/advisories/GHSA-rcfx-77hg-w2wv

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Classification

lane
Patch now
AI role
Attack on AI
categories
Infrastructure vulnerability
severity
2 · Disclosed vulnerability
fix status
Fix status unknown
targets
Framework / tooling
owasp llm top 10
LLM03:2025 Supply Chain
mitre atlas
no technique for these categories
tags
dns-rebinding
dates
happened 2 Dec 2025 · first reported 2 Dec 2025
origin
GitHub Advisory Database
Vulnerability record from NVD / the GitHub Advisory Database. This product uses the NVD API but is not endorsed or certified by the NVD.
record
confidence 0.95 · created 2026-10-18 07:00Z · updated 2026-10-18 18:20Z

Lane, AI role, categories and severity come from the classifier; the OWASP and ATLAS rows are derived from the categories. How these are assigned

Copy a brief

This record as a short Markdown brief, for a ticket, a chat or a coding agent.

the brief as text
# CVE-2025-66416: MCP Python SDK lacks default DNS rebinding protection

https://gcdradar.vercel.app/incidents/cve-2025-66416-mcp-python-sdk-lacks-default-dns-rebinding-pr · AIR-2025-0383 · closed 2025-12-02

- Lane: Patch now
- Severity: 2 (Disclosed vulnerability)
- Fix status: Fix status unknown
- First reported: 2025-12-02
- AI role: Attack on AI
- Products: Model Context Protocol Python SDK
- CVE ids: CVE-2025-66416
- CVSS: 7.6

## Summary

The Model Context Protocol Python SDK fails to enable DNS rebinding protection by default for HTTP servers. Attackers could exploit this via malicious websites to access local MCP resources.

## What to do

No action recorded; read the sources below and the vendor's advisory.

## Latest updates

- 2025-12-26: GHSA-rcfx-77hg-w2wv: FastMCP updated to MCP 1.23+ due to CVE-2025-66416 (https://github.com/advisories/GHSA-rcfx-77hg-w2wv)
- 2025-12-02: CVE-2025-66416: The MCP Python SDK, called `mcp` on PyPI, is a Python implementation of the Model Context Protocol (MCP). (https://nvd.nist.gov/vuln/detail/CVE-2025-66416)
- 2025-12-02: CVE-2025-66416: Model Context Protocol (MCP) Python SDK does not enable DNS rebinding protection by default (https://github.com/advisories/GHSA-9h52-p55h-vw2f)

## Sources

- 2025-12-02 GitHub Advisory Database: CVE-2025-66416: Model Context Protocol (MCP) Python SDK does not enable DNS rebinding protection by default https://github.com/advisories/GHSA-9h52-p55h-vw2f
- 2025-12-02 NVD: CVE-2025-66416: The MCP Python SDK, called `mcp` on PyPI, is a Python implementation of the Model Context Protocol (MCP). https://nvd.nist.gov/vuln/detail/CVE-2025-66416
- 2025-12-26 GitHub Advisory Database: GHSA-rcfx-77hg-w2wv: FastMCP updated to MCP 1.23+ due to CVE-2025-66416 https://github.com/advisories/GHSA-rcfx-77hg-w2wv

Verify against the vendor's advisory before changing production. Data CC BY-SA 4.0, https://gcdradar.vercel.app.

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