CVE-2026-9739: Google Mcp Toolbox For Databases

Critical severity, CVSS 9.4. EPSS: 0.2% chance of exploitation in the next 30 days.

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.

Affected products

• Google Mcp Toolbox For Databases

Published 2026-05-27. Last modified 2026-06-17.