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CVE-2026-9739

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

Critical9.4EPSS 0.28%
Published
Updated
Reserved
Assigned by
Google

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.

Scores

CVSS scores of CVE-2026-9739, by who scored it
Scored byCVSSScoreVector
GoogleCNA (assigner)4.0Critical9.4CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
NVDNVD · Awaiting Analysis4.0Critical9.4CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS (exploitation in 30 days)
0.28% · top 80% of all CVEs (6 Nov 2026)
CISA SSVC
Exploitation: none · Automatable: no · Technical impact: total
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: Critical 9.4.

Weakness

Affected products

Affected packages

From reviewed advisories of the GitHub Advisory Database.

References (2)

Sources

The same CVE in the primary databases and aggregators, to check against.

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Record last updated .