How severe is CVE-2025-66416?

CVE-2025-66416 has a CVSS 3.x base score of 8.1, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2025-66416 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (37th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2025-66416?

CVE-2025-66416 affects Lfprojects Mcp Python Sdk. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2025-66416?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2025-66416 have an EU (EUVD) identifier?

Yes. CVE-2025-66416 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-200273.

When was CVE-2025-66416 published?

CVE-2025-66416 was published on 2025-12-02 and last updated on 2026-06-17.

CVE-2025-66416

CVE-2025-66416 is a high-severity vulnerability in Lfprojects Mcp Python Sdk with a CVSS 3.x base score of 8.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-1188.

Key facts

Severity: High (CVSS 3.x base score 8.1)
CVSS v4: 7.6
EPSS exploit prediction: 0% (37th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-200273
Weakness: CWE-1188
Affected product: Lfprojects Mcp Python Sdk
Published: 2025-12-02
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2025-66416?: 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.
How severe is CVE-2025-66416?: CVE-2025-66416 has a CVSS 3.x base score of 8.1, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2025-66416 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (37th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-66416?: CVE-2025-66416 affects Lfprojects Mcp Python Sdk. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2025-66416?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2025-66416 have an EU (EUVD) identifier?: Yes. CVE-2025-66416 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-200273.
When was CVE-2025-66416 published?: CVE-2025-66416 was published on 2025-12-02 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:lfprojects:mcp_python_sdk:*:*:*:*:*:*:*:*

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