Insecure dfefault initialization of resource in MCP Python SDK - CVE-2025-66416
Published: December 18, 2025
Vulnerability identifier: #VU120189
CSH Severity: Low
CVSS v4: 2.1 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2025-66416
CWE-ID: CWE-1188
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to bypass implemented security restrictions.
The vulnerability exists due to software does not enable DNS rebinding protection by default for HTTP-based servers. A remote attacker can trick the victim into visiting a malicious website and to bypass same-origin policy restrictions by exploiting DNS rebinding and initiate requests to the local MCP server.
Successful exploitation of the vulnerability requires that an HTTP-based MCP server is running on the localhost without authentication using FastMCP with streamable HTTP or SSE transport, and has not configured TransportSecuritySettings.
Affected software
MCP Python SDK
Fusion Content-Aware Storage
watsonx.data
IBM Fusion HCI
Red Hat OpenShift AI (RHOAI)
Fusion Content-Aware Storage
watsonx.data
IBM Fusion HCI
Red Hat OpenShift AI (RHOAI)
How to mitigate CVE-2025-66416
Install updates from vendor's website.
MCP Python SDK - update to 1.23.0
Fusion Content-Aware Storage - update to 1.1.0
watsonx.data - update to 2.3.1
IBM Fusion HCI - update to 2.12.0
Red Hat OpenShift AI (RHOAI) - update to 2.25.1
Fusion Content-Aware Storage - update to 1.1.0
watsonx.data - update to 2.3.1
IBM Fusion HCI - update to 2.12.0
Red Hat OpenShift AI (RHOAI) - update to 2.25.1