CVE-2026-9739: Github.com/googleapis/mcp toolbox MCP Toolbox For Databases Vulnerable Vulnerability

CRITICAL
Advisory Identifier: GHSA-7pf3-8xx7-rvhf
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CWE-942
Published
Advisory Summary

CVE-2026-9739 is a CRITICAL mcp toolbox for databases vulnerable vulnerability (CWE-942: Permissive Cross-domain Security Policy with Untrusted Domains) affecting Github.com/googleapis/mcp toolbox libraries in the Go ecosystem. The issue involves mcp toolbox for databases vulnerable to dns rebinding attacks. Remediation is available by upgrading affected packages to version 1.2.0.

CVE-2026-9739 at a Glance

CVE Identifier CVE-2026-9739
GHSA Identifier GHSA-7pf3-8xx7-rvhf
Severity CRITICAL
CVSS v3.1 Base Score N/A
CWE Classification CWE-942: Permissive Cross-domain Security Policy with Untrusted Domains
Affected Product Github.com/googleapis/mcp toolbox
Package Ecosystem Go
Published Date
Last Updated

How to Fix CVE-2026-9739

To remediate this vulnerability, upgrade all affected Github.com/googleapis/mcp toolbox dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

github.com/googleapis/mcp-toolbox fixed: 1.2.0 
Upgrade github.com/googleapis/mcp-toolbox to 1.2.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for github.com/googleapis/mcp-toolbox

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-9739, inspect your project dependencies for Github.com/googleapis/mcp toolbox:

inspect dependencies for github.com/googleapis/mcp-toolbox

Analyze the terminal output to locate any version of Github.com/googleapis/mcp toolbox in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.2.0), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-942: Permissive Cross-domain Security Policy with Untrusted Domains, where the product uses a web-client protection mechanism such as a content security policy (csp) or cross-domain policy file, but the policy includes untrusted domains with which the web client is allowed to communicate. In Github.com/googleapis/mcp toolbox, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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.

CVE-2026-9739 Affected Github.com/googleapis/mcp toolbox Versions

1 component(s)
Fixed Versions:
1.2.0
Product / Package Ecosystem Affected Versions Fixed Version
github.com/googleapis/mcp-toolbox
golang/github.com/googleapis/mcp-toolbox
Go
< 1.2.0
1.2.0

References

NVD — CVE-2026-9739 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-9739
Github.com/googleapis/mcp toolbox Source Repository REPOSITORY
https://github.com/googleapis/mcp-toolbox/issues/3053
Github.com/googleapis/mcp toolbox Source Repository REPOSITORY
https://github.com/googleapis/mcp-toolbox/pull/3054
Security Fix Commit FIX COMMIT
https://github.com/googleapis/mcp-toolbox/commit/c4c7bd917e686de68e2be866cfe3872c3439efae
Github.com/googleapis/mcp toolbox Source Repository REPOSITORY
https://github.com/googleapis/mcp-toolbox

Frequently Asked Questions

What is CVE-2026-9739?
CVE-2026-9739 is a security vulnerability in Github.com/googleapis/mcp toolbox involving MCP Toolbox for Databases vulnerable to DNS rebinding attacks under CWE-942: Permissive Cross-domain Security Policy with Untrusted Domains.
Which Github.com/googleapis/mcp toolbox versions are affected?
Affected versions include releases prior to 1.2.0 across affected packages: github.com/googleapis/mcp-toolbox.
What version fixes CVE-2026-9739?
Upgrading to 1.2.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is github.com/googleapis/mcp-toolbox affected?
Yes, github.com/googleapis/mcp-toolbox is affected in releases prior to 1.2.0. Upgrade your dependency to 1.2.0 or later.
What CWE is associated with CVE-2026-9739?
CVE-2026-9739 is classified under CWE-942: Permissive Cross-domain Security Policy with Untrusted Domains (The product uses a web-client protection mechanism such as a Content Security Policy (CSP) or cross-domain policy file, but the policy includes untrusted domains with which the web client is allowed to communicate.).
How can I check Go dependencies for CVE-2026-9739?
Run the dependency tree command: 'inspect dependencies for github.com/googleapis/mcp-toolbox'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-7pf3-8xx7-rvhf",
  "modified" : "2026-07-01T20:54:22Z",
  "published" : "2026-05-28T00:30:29Z",
  "aliases" : [ "CVE-2026-9739" ],
  "summary" : "MCP Toolbox for Databases vulnerable to DNS rebinding attacks",
  "details" : "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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/googleapis/mcp-toolbox"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.2.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-9739"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/googleapis/mcp-toolbox/issues/3053"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/googleapis/mcp-toolbox/pull/3054"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/googleapis/mcp-toolbox/commit/c4c7bd917e686de68e2be866cfe3872c3439efae"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/googleapis/mcp-toolbox"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-942" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-01T20:54:22Z",
    "nvd_published_at" : "2026-05-27T23:16:48Z"
  }
}