CVE-2026-14541
Received Received - Intake

Authentication Bypass in Google mcp-toolbox via OAuth Audience Confusion

Publication date: 2026-07-31

Last updated on: 2026-07-31

Assigner: Google Inc.

Description
An authentication bypass and audience confusion vulnerability exists in the Google OAuth provider component of Google mcp-toolbox version 1.4.0. When a Google authService is initialized with mcpEnabled: true but lacks an explicitly defined audience or clientId, the ValidateMCPAuth pipeline for opaque tokens skips audience validation entirely. As a result, the toolbox will accept any valid Google OAuth access token—even those minted for unrelated ecosystem applications—granting unauthorized clients access to protected tools and data backends.

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Meta Information

Published
2026-07-31
Last Modified
2026-07-31
Generated
2026-07-31
AI Q&A
2026-07-31
EPSS Evaluated
N/A
NVD
CVE-2026-14541
EUVD
EUVD-2026-51381

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
google mcp-toolbox 1.4.0

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-287 When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.

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Executive Summary

This vulnerability is an authentication bypass in Google mcp-toolbox version 1.4.0. When the Google authService is set up with mcpEnabled true but without a defined audience or clientId, the system skips checking if an OAuth token is meant for it. This allows any valid Google OAuth token to access protected tools and data.

Impact Analysis

Attackers could use any valid Google OAuth token to gain unauthorized access to your protected tools and data backends. This could lead to data breaches, unauthorized actions, or misuse of your systems.

Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating GDPR and HIPAA requirements for data protection and access control. Non-compliance may result in legal penalties and reputational damage.

Mitigation Strategies

Update Google mcp-toolbox to a version where the Google OAuth provider component properly validates audience and clientId when mcpEnabled is true. Ensure all Google authService configurations explicitly define audience and clientId parameters.

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