CVE-2026-11717: Google Mcp Toolbox For Databases

Critical severity, CVSS 9.1. EPSS: 0.2% chance of exploitation in the next 30 days.

An authentication bypass vulnerability exists in the generic opaque token validation path (validateOpaqueToken) of googleapis/mcp-toolbox. When verifying an unparsed opaque token via an OAuth 2.0 introspection endpoint (RFC 7662), the toolbox decodes the response into an introspectResp struct where the Active field is declared as a pointer to a boolean (*bool). The code only explicitly rejects a token if the response contains a populated active field set to false (if introspectResp.Active != nil && !*introspectResp.Active). If an introspection endpoint responds with a payload that completely omits the mandatory active key, the internal variable remains nil, causing the conditional check to short-circuit. As a result, Toolbox accepts authorization tokens missing the "active" field, granting access to protected tools and underlying data sources.

Affected products

• Google Mcp Toolbox For Databases: from 1.0.0, up to and including 1.3.0

Published 2026-06-18. Last modified 2026-08-17.