CVE-2026-11718

Name: CVE-2026-11718
Creator: NVD / NIST
Published: 2026-06-18T14:17:20.19+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.3/10EPSS 0.20%

Last modified Jun 22, 2026

This CVE is reserved or awaiting analysis. Details will appear once published by NVD.

Description

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.

Metrics

CVSS 4.0

9.3/10

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:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS Probability

0.20%

10.5th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-287

References

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

Timeline

Published: Jun 18, 2026
Last Modified: Jun 22, 2026
Status: Awaiting Analysis

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Source: NVD / NIST