Critical severity · published May 27, 2026
CVE-2026-9739
Vulnerable to DNS rebinding attacks when using SSE (http://b/499408790)
9.4
CVSS
0.3%
EPSS
No
On KEV
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.
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 20% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MT
MCP Toolbox for Databases · Google
before PR 3054 (Fix CORS bypass) · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-9739
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-9739
github.com
https://github.com/googleapis/mcp-toolbox/issues/3053
github.com
https://github.com/googleapis/mcp-toolbox/pull/3054
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