Insecure BigQuery Access via dry-run Bypass in Google mcp-toolbox 0.16.1-1.4.0
CVE-2026-14538 Published on July 31, 2026
BigQuery Dataset Allowlist Bypass via Metadata Dry-Run in MCP Toolbox
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.
Weakness Types
What is an AuthZ Vulnerability?
The software does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action.
CVE-2026-14538 has been classified to as an AuthZ vulnerability or weakness.
What is an AuthZ Vulnerability?
The software performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. This allows attackers to bypass intended access restrictions.
CVE-2026-14538 has been classified to as an AuthZ vulnerability or weakness.
Affected Versions
Google mcp-toolbox:- Version 0.16.1, <= 1.4.0 is affected.