Authentication Bypass in github.com/googleapis/mcp-toolbox (CVE-2026-11718)
Summary
Authentication bypass in github.com/googleapis/mcp-toolbox (CVE-2026-11718). Confidential information can be exposed externally. Mitigation: upgrade to 1.4.0 or later.
Original description
The description as published by the source.
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.
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-11718 has been found in github.com/googleapis/mcp-toolbox.
Confidential information can be exposed externally. CVSS score: 9.1/10.
What to do: upgrade github.com/googleapis/mcp-toolbox to 1.4.0 or later.
If unsure, ask your IT team or search "github.com/googleapis/mcp-toolbox CVE-2026-11718" on the vendor's site.
CVE-2026-11718 (github.com/googleapis/mcp-toolbox) — CWE-287 / CVSS v3 9.1
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 1.4.0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Authentication bypass (CWE-287) exists in github.com/googleapis/mcp-toolbox.
Check the vendor advisory for the affected versions of github.com/googleapis/mcp-toolbox.
Severity: Critical (CVSS 9.1/10). Confidential information can be exposed externally.
Update to 1.4.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'github.com/googleapis/mcp-toolbox' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
grep -r 'github.com/googleapis/mcp-toolbox' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
github.com/googleapis/mcp-toolboxを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade github.com/googleapis/mcp-toolbox to 1.4.0ステージング環境で 1.4.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory nvd.nist.gov
- advisory github.com
- advisory github.com
- package github.com
- patch github.com