Auth bypass in Google Mcp-Toolbox
CVE-2026-14541
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.
Vulnerability class: Broken Authentication
EPSS: 0.002 (14.3th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.
Affected products
- Google Mcp-toolbox — versions 1.4.0
- Google Mcp_toolbox_for_databases — versions 1.4.0
Weakness classification (CWE)
References
- cve-coordination@google.com (Patch, Issue Tracking)
Frequently asked questions
- What is CVE-2026-14541?
- CVE-2026-14541 is a high-severity vulnerability in Google Mcp-Toolbox, classified under Improper Authentication. CVSS score: 7.5/10. Published 2026-07-31.
- How severe is CVE-2026-14541?
- High severity. CVSS v3 base score is 7.5 out of 10.