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CVE-2026-14541 – Authentication Bypass – Google MCP Toolbox for Databases v1.4.0

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Summary

CVE-2026-14541 is an authentication bypass and audience confusion vulnerability in the Google OAuth provider component of Google MCP Toolbox for Databases version 1.4.0. When the Google authService is configured with mcpEnabled: true but no explicit audience or clientId is defined, the token validation pipeline skips audience verification entirely, allowing any valid Google OAuth access token — regardless of its intended audience or application — to be accepted by the server. This vulnerability carries a CVSS 4.0 score of 8.0 (High) and is exploitable remotely with no privileges required.

Technical details

  • Root cause: The ValidateMCPAuth pipeline for opaque tokens in the Google OAuth provider omits audience validation when mcpEnabled: true is set without an explicitly configured audience or clientId (CWE-287: Improper Authentication).
  • Trigger conditions: A Google authService must be initialized with mcpEnabled: true and lack an explicit audience or clientId in its configuration.
  • Attack vector: Network-reachable with no authentication prerequisites. An attacker needs only any valid Google OAuth access token — including one obtained for a completely unrelated Google-ecosystem application — to exploit the flaw.
  • Impact: Unauthorized clients can present any valid Google OAuth token to the vulnerable toolbox instance and gain access to protected tools and database backends, resulting in high confidentiality and integrity impact on the vulnerable component.

Affected software

  • Google MCP Toolbox for Databases version 1.4.0

Severity

CVSS 4.0 base score: 8.0 (High)
Vector string: 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

Mitigation and recommended actions

  • Immediate: Upgrade to Google MCP Toolbox for Databases version 1.5.0 or later. The fix — enforcing that audience or clientId must be explicitly defined when mcpEnabled: true — was introduced in v1.5.0 (released June 18, 2026). The current latest version is v1.8.0.
  • Workaround: If an immediate upgrade is not feasible, explicitly define the audience or clientId parameter in your Google authService configuration wherever mcpEnabled: true is set. This prevents the audience validation step from being skipped.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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