Vulnerability · Published Jul 31, 2026 · Assigned by Google
CVE-2026-14538BigQuery Dataset Allowlist Bypass via Metadata Dry-Run in MCP Toolbox
Medium 5.7
In plain English
A medium-severity incorrect authorization in mcp-toolbox from Google. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 10% of all known vulnerabilities).
Official description
An improper authorization and security-boundary bypass vulnerability in the bigquery-execute-sql tool component of Google mcp-toolbox versions 0.16.1 through 1.4.0 allows an authenticated attacker to bypass allowedDatasets validation checks. The toolbox relies on the BigQuery dry-run API to enforce dataset restrictions, but due to a fail-open logic flaw, it bypasses validation when the API returns an empty array for specialized constructs. This allows the attacker to extract structural DDL schemas for explicitly excluded datasets via INFORMATION_SCHEMA, and access downstream federated row data via EXTERNAL_QUERY connections.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| mcp-toolbox | 0.16.1 – through 1.4.0 |
Weakness: CWE-285, CWE-863 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N/E:U