CVE-2026-9739Network attack vector

Database tool invocation via wildcard SSE origin

Published May 27, 2026 · Updated May 27, 2026

Cross-origin policy bypass in Google MCP Toolbox for Databases before 1.2.0 allows remote attackers to invoke database tools through SSE. The sseHandler in internal/server/mcp.go overwrites the configured CORS policy with a wildcard Access-Control-Allow-Origin header during SSE initialization. Exploitation requires a Toolbox connection using SSE under MCP specification v2024-11-05 and a user to visit an attacker-controlled site; available tool permissions bound the resulting database access.

CVSS severity9.4
Critical
EPSS probability0.28%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Cross-origin policy bypass in Google MCP Toolbox for Databases before 1.2.0 allows remote attackers to invoke database tools through SSE. The sseHandler in internal/server/mcp.go overwrites the configured CORS policy with a wildcard Access-Control-Allow-Origin header during SSE initialization. Exploitation requires a Toolbox connection using SSE under MCP specification v2024-11-05 and a user to visit an attacker-controlled site; available tool permissions bound the resulting database access.

The record

CVE
CVE-2026-9739
Published
May 27, 2026
Updated
May 27, 2026
Vendor
Go standard library
Product
MCP Toolbox for Databases
Classifications
CWE-942, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 27, 2026CVE publishedPublication date reported by the CVE source.
  2. May 27, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <PR 3054 (Fix CORS bypass)

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Go standard library · MCP Toolbox for Databasesversion=0 <PR 3054 (Fix CORS bypass)

Published CVSS scores

9.4GitHub Advisory DatabaseCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-942Permissive Cross-domain Security Policy with Untrusted Domains
T1204.001User Execution: Malicious Link

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo