googleapis/mcp-toolbox: authentication bypass vulnerability in the generic opaque token validation path (validateOpaqueToken)

緊急 9.1CVE-2026-11718 · GHSA-wcpr-6g7x-p44r · GO-2026-5706 · 18/06/2026 公開 · 26/10/2026 更新

要点

CVE-2026-11718 は github.com/googleapis/mcp-toolbox, mcp toolbox for databases (google) に影響する深刻度「緊急」 (CVSS 9.1) の脆弱性です。
今後30日間に悪用される確率（EPSS）：0.18%（全脆弱性の 8.1% より高い）。
対処：1.4.0 以降に更新してください。

パッケージ	影響を受けるバージョン	修正済みバージョン
github.com/googleapis/mcp-toolbox Go	`< 1.4.0`	`1.4.0`
mcp toolbox for databases google	`≥ 1.0.0, ≤ 1.3.0`	修正版なし

概要

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.

NVD の説明

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.