CVE-2026-9739

Name: CVE-2026-9739
Creator: NVD / NIST
Published: 2026-05-27T23:16:48.573+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.4/10EPSS 0.28%

Last modified Jun 17, 2026

This CVE is reserved or awaiting analysis. Details will appear once published by NVD.

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.

Metrics

CVSS 4.0

9.4/10

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/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 Probability

0.28%

19.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-942

References

Timeline

Published: May 27, 2026
Last Modified: Jun 17, 2026
Status: Awaiting Analysis

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Source: NVD / NIST