CVE-2025-66416

highpriority · track · 32OT risk · elevatedEPSS 0.005 · 43 %ileDEEUUS
grimoire priorityP2 · Scheduled
Exploitable?
—
no known exploitation
Likely / severe?
0.51% (43rd) EPSS
CVSS 8.1 · high
Is it mine?
5 products
Check your exposure
Who says so?
5 sources
cnnvd · enisa_euvd · osv · cert_bund

EPSS · scored 2026-10-27

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.

01

cvss

Technical severity, 0–10. One row per scoring source.

8.1
010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · medium–high · 4.9–8.1

v3.18.1highCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:Nprimary · NVD / NIST USexploitability 2.8 · impact 5.2
v4.07.6highCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:Nsecondary · ENISA EU
v4.07.6highCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Xsecondary · security-advisories@github.com
v4.04.9mediumCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Xsecondary · CVSS-BT (t0sche)
02

ssvc

A stakeholder decision — act, attend, or track — from exploitation and impact.

Exploitation: none · Automatable: no · Technical Impact: totalcoordinatorcisa_ssvcUS
03

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-1188USCWE-1188USCWE-350US
04

affected products (5)

Products and version ranges known to be affected.

05

advisories (3)

Vendor and ecosystem advisories describing this.

  • WID-SEC-W-2026-0120Red Hat Satellite (satellite/foreman-mcp-server-rhel9): Mehrere SchwachstellenDeutsch2026-01-14csaf · cert_bundDE

    Ein entfernter, authentisierter oder anonymer Angreifer kann mehrere Schwachstellen in Red Hat Satellite ausnutzen, um einen Denial of Service Angriff durchzuführen oder Sicherheitsmaßnahmen zu umgehen.

  • GHSA-9h52-p55h-vw2fModel Context Protocol (MCP) Python SDK does not enable DNS rebinding protection by default2025-12-02ghsa · osvUS

    ### 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 localhost.

  • PYSEC-2026-1617Model Context Protocol (MCP) Python SDK does not enable DNS rebinding protection by default2026-07-07vendor · osvUS

    ### 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 localhost.

06

also known as (6)

Other names and identifiers for this entity.

07

sources

Which sources assert this record, and when.

cnnvdenisa_euvdosvcert_bundnvdNVDCVE.orgMITRE
published 2025-12-02modified 2026-10-18
08

references (8)

External citations — patches, advisories, analysis.

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