CVE-2025-66416
BaseFortify
Publication date: 2025-12-02
Last updated on: 2026-03-10
Assigner: GitHub, Inc.
Description
Description
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| lfprojects | mcp_python_sdk | to 1.23.0 (exc) |
Helpful Resources
Exploitability
| CWE ID | Description |
|---|---|
| CWE-1188 | The product initializes or sets a resource with a default that is intended to be changed by the product's installer, administrator, or maintainer, but the default is not secure. |
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?
The vulnerability exists in the MCP Python SDK prior to version 1.23.0, where DNS rebinding protection is not enabled by default for HTTP-based servers. This allows a malicious website to bypass same-origin policy restrictions and send requests to a local MCP server running on localhost without authentication, potentially invoking tools or accessing resources on behalf of the user. This issue occurs when using FastMCP with streamable HTTP or SSE transport and no TransportSecuritySettings configured. It does not affect servers using stdio transport. The vulnerability is fixed in version 1.23.0.
How can this vulnerability impact me? :
If you run an HTTP-based MCP server locally without authentication and without proper security settings, a malicious website could exploit DNS rebinding to bypass browser security policies and send unauthorized requests to your local MCP server. This could lead to unauthorized invocation of tools or access to resources exposed by the MCP server on your behalf, potentially compromising your local environment or data.
What immediate steps should I take to mitigate this vulnerability?
To mitigate this vulnerability, upgrade the MCP Python SDK to version 1.23.0 or later, which enables DNS rebinding protection by default. Additionally, avoid running HTTP-based MCP servers locally without authentication, and configure TransportSecuritySettings properly if using FastMCP with streamable HTTP or SSE transport.