Vulnerability · Published Jul 31, 2026 · Assigned by Google
CVE-2026-14541Authentication Bypass and Audience Confusion in MCP Toolbox OAuth Provider
High 8.0
In plain English
A high-severity improper authentication in mcp-toolbox from Google. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 17% of all known vulnerabilities).
Official 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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| mcp-toolbox | 1.4.0 |
Weakness: CWE-287 · 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