Vulnerability Description
Vulnerable to DNS rebinding attacks when using SSE (http://b/499408790). During the beta phase, we implemented `allowed-origins` and `allowed-hosts` flags to align with MCP security guidelines. However, the hardcoded `Access-Control-Allow-Origin: *` header in the SSE initialization handler was inadvertently retained. This vulnerability specifically impacts users connecting via Toolbox using SSE under specification v2024-11-05.
Related Weaknesses (CWE)
References
- https://github.com/googleapis/mcp-toolbox/issues/3053
- https://github.com/googleapis/mcp-toolbox/pull/3054
FAQ
What is CVE-2026-9739?
CVE-2026-9739 is a documented vulnerability. Vulnerable to DNS rebinding attacks when using SSE (http://b/499408790). During the beta phase, we implemented `allowed-origins` and `allowed-hosts` flags to align with MCP security guidelines. Howeve...
How severe is CVE-2026-9739?
CVSS scoring is not yet available for CVE-2026-9739. Check NVD for updates.
Is there a patch for CVE-2026-9739?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.