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CVE-2026-9739

37
FAUCET Score

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.

First published: May 27, 2026Last modified: May 27, 2026

Impacted Technologies

VendorProductVersion(s)CPE
GoogleMCP Toolbox For Databases
>= 0, < PR 3054 (Fix CORS bypass)CNA affecteddefault unaffected

CVSS Data

CVSS version used by this source: 4.0

9.4CRITICAL

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

Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
ACTIVE
VS Confidentiality
HIGH
VS Integrity
HIGH
VS Availability
HIGH
SS Confidentiality
HIGH
SS Integrity
HIGH
SS Availability
HIGH
Exploit Maturity
NOT_DEFINED
CvssVersion
4.0

Exploit Intelligence

EPSS Score
0.28%
Probability of exploitation in next 30 days
EPSS Percentile
20.1%
Percentile rank of EPSS score among Peer Group
As of 2026-07-25
Model: v2026.06.15
This CVE's current EPSS score of 0.0028 is in the 20th percentile among its peer group of 834 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.8 Bluesky, 0.5 Mastodon, and 1.2 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.1 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (1)

gopatch availablevia ghsa
Product: github.com/googleapis/mcp-toolboxFixed in: 1.2.0

Vendor Advisories (1)

goGHSA-7pf3-8xx7-rvhfcritical

MCP Toolbox for Databases vulnerable to DNS rebinding attacks

May 28, 2026

References

github.com / googleapis/mcp-toolbox/issues/3053
github.com / googleapis/mcp-toolbox/pull/3054