CVE-2026-14541

Authentication Bypass and Audience Confusion in MCP Toolbox OAuth Provider

Published Jul 31, 2026 CVSS 4.0 · 8 High EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
First Time appeared Google
Google mcp-toolbox
Vendors & Products Google
Google mcp-toolbox
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
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.
Title Authentication Bypass and Audience Confusion in MCP Toolbox OAuth Provider
Weaknesses CWE-287
References
Metrics cvssV4_0

{'score': 8, '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/E:U'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
Google
Published
Updated
Jul 31, 2026, 4:14 PM
Reserved
Jul 3, 2026, 3:38 AM
Status
Analyzed
Published
Jul 31, 2026, 3:16 AM
Modified
Oct 23, 2026, 11:10 PM