---
cve: "CVE-2026-11717"
severity: "CRITICAL"
cvss: 9.3
epss: "0.2%"
vendor: "Google"
kev: false
exploited: false
published: "2026-06-18 14:17:20"
tags: [cve, security, critical]
source: tsecurity.de CVE-Dossier
exported: "2026-10-23T09:00:59+02:00"
---

# CVE-2026-11717

> 9.3 CRITICAL · 🧪 PoC

## Beschreibung

An authentication bypass vulnerability exists in the generic opaque token validation path (validateOpaqueToken) of googleapis/mcp-toolbox.

When verifying an unparsed opaque token via an OAuth 2.0 introspection endpoint (RFC 7662), the toolbox decodes the response into an introspectResp struct where the Active field is declared as a pointer to a boolean (*bool). The code only explicitly rejects a token if the response contains a populated active field set to false (if introspectResp.Active != nil && !*introspectResp.Active). If an introspection endpoint responds with a payload that completely omits the mandatory active key, the internal variable remains nil, causing the conditional check to short-circuit. As a result, Toolbox accepts authorization tokens missing the "active" field, granting access to protected tools and underlying data sources.

## CNA-Record (Kanon, cvelistV5)

- CNA: **Google**
- State: PUBLISHED
- Stand: 2026-06-18 12:23:15
- CNA-CVSS: **9.3** (`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`)

## CISA-Anreicherung (vulnrichment/ADP)

- CISA-SSVC (Coordinator, v2.0.3):
  - Exploitation: **none**
  - Automatable: **yes**
  - Technical Impact: **total**

## CVSS-Vektor

```
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
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Keine | bad |
| UI Interaktion | Keine | bad |

## Schwachstellen-Klasse

- **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.

## Angriffsmuster (CAPEC)

- [CAPEC-22 — Exploiting Trust in Client](https://capec.mitre.org/data/definitions/22.html) _(Severity: High)_
- [CAPEC-57 — Utilizing REST's Trust in the System Resource to Obtain Sensitive Data](https://capec.mitre.org/data/definitions/57.html) _(Severity: Very High)_
- [CAPEC-114 — Authentication Abuse](https://capec.mitre.org/data/definitions/114.html) _(Severity: Medium)_
- [CAPEC-115 — Authentication Bypass](https://capec.mitre.org/data/definitions/115.html) _(Severity: Medium)_
- [CAPEC-151 — Identity Spoofing](https://capec.mitre.org/data/definitions/151.html) _(Severity: Medium)_
- [CAPEC-194 — Fake the Source of Data](https://capec.mitre.org/data/definitions/194.html) _(Severity: Medium)_
- [CAPEC-593 — Session Hijacking](https://capec.mitre.org/data/definitions/593.html) _(Severity: Very High)_
- [CAPEC-633 — Token Impersonation](https://capec.mitre.org/data/definitions/633.html) _(Severity: Medium)_

## ATT&CK-Techniken

- [T1040 — Network Sniffing](https://attack.mitre.org/techniques/T1040/)
- [T1548 — Abuse Elevation Control Mechanism](https://attack.mitre.org/techniques/T1548/)
- [T1185 — Browser Session Hijacking](https://attack.mitre.org/techniques/T1185/)
- [T1550.001 — Use Alternate Authentication Material:Application Access Tok](https://attack.mitre.org/techniques/T1550/001/)
- [T1563 — Remote Service Session Hijacking](https://attack.mitre.org/techniques/T1563/)
- [T1134 — Access Token Manipulation](https://attack.mitre.org/techniques/T1134/)

## Referenzen

- <https://github.com/googleapis/mcp-toolbox/pull/3341>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/sicherheitsluecken/cve-2026-11717/) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI WID (CSAF)_