CVE-2026-11718

An authentication bypass vulnerability exists in the generic opaque token validation path (validateOpaqueToken) of googleapis/mcp-toolbox. When the toolbox validates an opaque token via an OAuth 2.0 introspection endpoint (RFC 7662), it decodes the response into an introspectResp struct. However, the subsequent claim-checking logic (validateClaims) evaluates the issuer condition as if a.issuer != "" && iss != "". If the external OAuth provider's introspection response omits the optional iss (issuer) field completely, the variable iss defaults to an empty string. This causes the conditional block to evaluate to false and be skipped silently. Consequently, the application accepts tokens issued by unauthorized or unintended third-party identity providers.

CVSS v3 9.1 CRITICAL

9.1^/10

CVSS v3 : CRITICAL

Vector :

Exploitability : 3.9 / Impact : 5.2

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

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

Configurations

Configuration 1 (hide)

cpe:2.3:a:google:mcp_toolbox_for_databases:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-06-18 14:17

Updated : 2026-08-17 16:04

NVD link : CVE-2026-11718

Mitre link : CVE-2026-11718

CVE.ORG link : CVE-2026-11718

JSON object : View

Products Affected

google

mcp_toolbox_for_databases

CWE

CWE-287

Improper Authentication

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