CVE-2026-14541: An authentication bypass and audience confusion vulnerability exists in the Google OAuth provider component of Google mc

What it is

CVE-2026-14541, published 2026-07-31 and now in "Analyzed" status, is an authentication bypass / audience-confusion flaw (CWE-287) in the Google OAuth provider of Google's mcp-toolbox for databases, version 1.4.0. The existing summary covers the mechanism; the page adds the severity rating and the fix location.

How it works

When a Google authService is initialized with mcpEnabled: true but no explicitly defined audience or clientId, the ValidateMCPAuth pipeline for opaque tokens skips audience validation entirely. Any valid Google OAuth access token — including one minted for an unrelated ecosystem application — is then accepted, reaching protected tools and data backends.

Severity

CVSS 4.0 base score 8.0 (HIGH), vector CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N. Notable properties: network-attackable, no privileges and no user interaction required, high confidentiality and integrity impact, no availability impact. Exploit maturity is marked unproven (E:U).

Preconditions / Affected

• Product: google mcp-toolbox for databases, version 1.4.0.
• A Google authService configured with mcpEnabled: true.
• No explicit audience or clientId set on that service.
• Opaque-token validation path (the code branch that skips the audience check).

What to do

The advisory's sole reference is the upstream fix:

https://github.com/googleapis/mcp-toolbox/pull/3450

Track that PR for the patched release and update off 1.4.0. Until patched, set an explicit audience/clientId on any Google authService so audience validation is not bypassed.

Caveats

The page states only that the fix lives in PR #3450 and does not name a fixed version number, so confirm which release carries it before relying on a version bump. Exploit maturity is listed as unproven.