Connect your agent
AdvisoriesCriticalCheck your lockfilePluginHow it worksPricing Connect your agent

Advisory record · GHSA-9h52-p55h-vw2f

Model Context Protocol (MCP) Python SDK does not enable DNS rebinding protection by default

CVSS 7.6 HighEPSS 0.0054 · 45th percentile

Published by the GitHub Advisory Database at 2 Dec 2025, 16:52 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
mcpPyPI<1.23.01.23.0
Identifiers
GHSA-9h52-p55h-vw2f · CVE-2025-66416 · PYSEC-2026-1617
Weakness (CWE)
CWE-350 · CWE-1188
Tags
Published
2 Dec 2025
Updated
10 Sept 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Model Context Protocol (MCP) Python SDK versions before 1.23.0 do not enable DNS rebinding protection by default for HTTP-based servers. A malicious website could use DNS rebinding to send requests to an unauthenticated FastMCP server running on localhost with streamable HTTP or SSE transport, invoking its tools or accessing its resources as the user. Upgrade the mcp package to version 1.23.0 or later; servers using custom low-level configurations should explicitly set TransportSecuritySettings.

Written 5 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
7.6 High 4.0 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 CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0054, the 45th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:34 UTC First seen by agentprime
  2. 31 Oct 2026, 14:34 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.