CVE-2026-11718

CRITICALPre-NVD 9.39.3—
EchelonGraph scoreMEDIUM confidence

This critical-severity CVE scores 9.3 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.2%, top 89% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
9.3
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 0%CVSS: 9.3Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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 v3
9.3
EG Score
9.3(medium)
EPSS
10.5%
KEV
Not listed

Published

June 18, 2026

Last Modified

June 22, 2026

Advisory Details (1)

Auto-updated Jun 22, 2026
Patch available. Sources: github_pr.
github_pr Patch Available

fix(auth/generic): enforce issuer presence in opaque token validation

Patch available: googleapis/mcp-toolbox v1.4.0 (PR #3360 merged 2026-06-04)

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

Vendor Advisories for CVE-2026-11718(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(1 across 1 ecosystem)
Go(1)
PackageVulnerable rangeFixed inDependents
github.com/googleapis/mcp-toolbox—1.4.0—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 48× in last 7d / 109× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 109 total refreshes for this CVE.

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  73. 2026-06-22 21:40 UTCEG score recompute▲ 9.30
  74. 2026-06-22 21:36 UTCNVD updateCVSS v3 → 9.3 · CVSS v4 → 9.3
  75. 2026-06-22 14:25 UTCEPSS rescore

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-11718?
CVE-2026-11718 is a critical vulnerability published on June 18, 2026. 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,…
When was CVE-2026-11718 disclosed?
CVE-2026-11718 was first published in the National Vulnerability Database on June 18, 2026, with the most recent update on June 22, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-11718 actively exploited?
CVE-2026-11718 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 10.5% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-11718?
CVE-2026-11718 has a CVSS v3 base score of 9.3 (NVD).
How do I remediate CVE-2026-11718?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-11718, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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