CVE-2026-11718

PUBLISHED
Published: 18 Jun 2026, 11:52
Last modified:18 Jun 2026, 11:52

Vulnerability Summary

Overall Risk (default)
high
70/100
CVSS Score
9.3 CRITICAL
v4.0 (cve.org)
EPSS Score
No data
KEV
Not listed
Ransomware
No reports
Public exploits
None found
Dark Web
Not detected

Timeline

18 Jun 2026, 11:52
Published
Vulnerability first disclosed

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.

CVSS Metrics

  • v4.0•CRITICAL•Score: 9.3CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Techniques & Countermeasures

  • CWE-287•Improper Authentication

    When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.

Affected Systems

  • google•mcp toolbox for databases (googleapis/mcp-toolbox)

    ≥ 1.0.0, ≤ 1.3.0

References (1)