cve.bz

CVE-2026-9739

9.4 criticalEPSS 0.3%

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.

CVSS 4.0
9.4CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
EPSS
0.3% chance of exploitation in the next 30 days; higher than 20% of CVEs (scores of 2026-10-25)
CWE
CWE-942
Published
Modified
Record from
the NVD, synced

Packages (OSV)

AdvisoryEcosystemPackageAffectedFixed in
GHSA-7pf3-8xx7-rvhfGogithub.com/googleapis/mcp-toolbox<1.2.01.2.0
GO-2026-5870Gogithub.com/googleapis/mcp-toolbox<1.2.01.2.0

References

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