VulnerabilityAwaiting Analysis

CVE-2026-9739

Vulnerable to DNS rebinding attacks when using SSE (http://b/499408790).

CRITICAL 9.4EPSS 0.28%

Does this matter?

High impact if exploited, but EPSS currently rates exploitation as unlikely (0.28%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.

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.

CVSS 4.0: 9.4 CRITICALCVSS: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/M
EPSS: 0.28% probability · 20th percentile
CISA KEV: Not listed
Weakness: CWE-942
Source: cve-coordination@google.com

References

Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.