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VulnerabilityPublished

CVE-2026-9739: Google MCP Toolbox for Databases · Permissive Cross-domain Policy with Untrusted Domains

Affects Google MCP Toolbox for DatabasesSource CVE Database V5

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Not known to be exploited · CVSS 9.4 Critical : upgrade to PR 3054 (Fix CORS bypass) as a priority.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 4.0 base score
9.4Critical
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 20% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in PR 3054 (Fix CORS bypass)
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 evidence

  1. Disclosed: evidence found.

    CVE published 27 May 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

Upgrade Google MCP Toolbox for Databases to PR 3054 (Fix CORS bypass).

Affected software

ProductAffectedFixed in
GoogleMCP Toolbox for DatabasesAffected
  • =0
Fixed in
  • PR 3054 (Fix CORS bypass)

AI-suggested

If you cannot patch yet, avoid using SSE connections under specification v2024-11-05 with MCP Toolbox or implement network-level controls to restrict untrusted domains if possible.

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.

References

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