---
title: "CVE-2026-9739: MCP Toolbox for Databases vulnerable to DNS rebinding attacks"
url: https://erroneo.us/security/cve/CVE-2026-9739/
description: "CVE-2026-9739 (github.com/googleapis/mcp-toolbox (Go)): Vulnerable to DNS rebinding attacks when using SSE (http://b/499408790). During the beta phase, we…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-05-27
date_modified: 2026-07-01
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-9739"
kev: false
cvss: 9.4
epss: 0.00237
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-9739: MCP Toolbox for Databases vulnerable to DNS rebinding attacks

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.2% , percentile 14: FIRST’s model estimates a 0.2% chance of exploitation activity in the next 30 days, higher than 14% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Only applies if your dependency tree includes github.com/googleapis/mcp-toolbox (Go) < 1.2.0, fixed in 1.2.0 . Check your lockfile, including transitive dependencies.

## What it is

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.

## Affected packages

- Go `github.com/googleapis/mcp-toolbox` < 1.2.0 → fixed: 1.2.0

## Affected products (CVE record)

- Google MCP Toolbox for Databases: < PR 3054 (Fix CORS bypass)

## Severity

- Google CVSS 4.0: 9.4 `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`
- GitHub CVSS 4.0: 9.4 `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`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable no , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.24% probability of exploitation activity in the next 30 days; percentile 14.

## Sources

- [GitHub Advisory GHSA-7pf3-8xx7-rvhf](https://github.com/advisories/GHSA-7pf3-8xx7-rvhf)
- [CVE.org record CVE-2026-9739](https://www.cve.org/CVERecord?id=CVE-2026-9739)
- [NVD entry CVE-2026-9739](https://nvd.nist.gov/vuln/detail/CVE-2026-9739)
- [github.com](https://github.com/googleapis/mcp-toolbox/issues/3053)
- [github.com](https://github.com/googleapis/mcp-toolbox/pull/3054)
- [github.com](https://github.com/googleapis/mcp-toolbox/commit/c4c7bd917e686de68e2be866cfe3872c3439efae)

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Source page: https://erroneo.us/security/cve/CVE-2026-9739/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt