Vulnerability · Published May 27, 2026 · Assigned by Google
CVE-2026-9739
Critical 9.4
In plain English
A critical-severity security flaw in MCP Toolbox for Databases from Google. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 20% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/googleapis/mcp-toolbox | 1.2.0 | GHSA-7pf3-8xx7-rvhf |
| Go | github.com/googleapis/mcp-toolbox | 1.2.0 | GO-2026-5870 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| MCP Toolbox for Databases | 0 – before PR 3054 (Fix CORS bypass) |
Weakness: CWE-942 · 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