CVE-2026-9739

published 2026-05-27

CVE-2026-9739: Vulnerable to DNS rebinding attacks when using SSE (http://b/499408790). During the beta phase, we implemented `allowed-origins` and `allowed-hosts` flags to…

Priority P3 48 critical 9.4 CVSS 4.0

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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

2 ranges

Vendor	Product	Version range	Fixed in
github.com	googleapis_mcp-toolbox	>= 0 < 1.2.0	1.2.0
google	mcp_toolbox_for_databases	< PR 3054 (Fix CORS bypass)	PR 3054 (Fix CORS bypass)

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CWE-942