Authentication Bypass Vulnerability in Google APIs MCP Toolbox
CVE-2026-11718

9.3CRITICAL

Key Information:

Vendor

Google
Status
Mcp Toolbox For Databases (googleapis/mcp-toolbox)
Vendor
CVE Published:
18 June 2026

What is CVE-2026-11718?

An authentication bypass vulnerability has been identified in the Google APIs MCP Toolbox, specifically within the token validation process via the OAuth 2.0 introspection endpoint. During the validation of opaque tokens, if the external OAuth provider's response lacks the optional issuer (iss) field, it defaults to an empty string. This flaw allows malicious actors to exploit the claim-checking logic, leading to unauthorized acceptance of tokens from unintended identity providers. It is essential for users and administrators to review and implement recommended security measures to mitigate this risk.

Affected Version(s)

MCP Toolbox for Databases (googleapis/mcp-toolbox) 1.0.0 <= 1.3.0

References

https://github.com/googleapis/mcp-toolbox/pull/3360

CVSS V4

Score:
9.3
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

HaoNH Leader Redteam From VINCSS ( Member Of Vingroup ).
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