CVE-2026-9739

DNS Rebinding via SSE Causing CORS Bypass in MCP Toolbox for Databases

Published May 27, 2026 CVSS 4.0 · 9.4 Critical EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-7pf3-8xx7-rvhf MCP Toolbox for Databases vulnerable to DNS rebinding attacks
History
Type Values Removed Values Added
First Time appeared Google
Google mcp Toolbox For Databases
Vendors & Products Google
Google mcp Toolbox For Databases
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
Title DNS Rebinding via SSE Causing CORS Bypass in MCP Toolbox for Databases
Type Values Removed Values Added
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.
Weaknesses CWE-942
References
Metrics cvssV4_0

{'score': 9.4, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
Google
Published
Updated
May 28, 2026, 1:20 PM
Reserved
May 27, 2026, 5:31 PM
Status
Awaiting Analysis
Published
May 27, 2026, 11:16 PM
Modified
Oct 26, 2026, 12:10 PM