Vulnerability-Lookup

GHSA-WCPR-6G7X-P44R

Vulnerability from github – Published: 2026-06-18 15:32 – Updated: 2026-06-19 16:59

Summary

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

Details

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.

Severity

9.3 (Critical)


                  
                    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

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/googleapis/mcp-toolbox"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.4.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-11718"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-287"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-19T16:59:25Z",
    "nvd_published_at": "2026-06-18T14:17:20Z",
    "severity": "CRITICAL"
  },
  "details": "An authentication bypass vulnerability exists in the generic opaque token validation path (validateOpaqueToken) of googleapis/mcp-toolbox.\n\nWhen 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 != \"\" \u0026\u0026 iss != \"\". If the external OAuth provider\u0027s 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.",
  "id": "GHSA-wcpr-6g7x-p44r",
  "modified": "2026-06-19T16:59:25Z",
  "published": "2026-06-18T15:32:01Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-11718"
    },
    {
      "type": "WEB",
      "url": "https://github.com/googleapis/mcp-toolbox/pull/3360"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/googleapis/mcp-toolbox"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "googleapis/mcp-toolbox: authentication bypass vulnerability in the generic opaque token validation path (validateOpaqueToken)"
}

CVE-2026-11718 (GCVE-0-2026-11718)

Vulnerability from cvelistv5 – Published: 2026-06-18 11:52 – Updated: 2026-06-18 13:53

Summary

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.

Severity

9.3 (Critical)


                        
                          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

SSVC

Exploitation: none Automatable: yes Technical Impact: total

CISA Coordinator (v2.0.3)

CWE

CWE-287 - Improper Authentication

Assigner

Google

References

1 reference

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

Impacted products

1 product

Vendor	Product	Version
Google	MCP Toolbox for Databases (googleapis/mcp-toolbox)	Affected: 1.0.0 , ≤ 1.3.0 (semver)

Credits

HaoNH Leader Redteam From VINCSS ( Member Of Vingroup ).

Show details on NVD website

JSON

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                "role": "CISA Coordinator",
                "timestamp": "2026-06-18T13:01:08.666194Z",
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Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-WCPR-6G7X-P44R

CVE-2026-11718 (GCVE-0-2026-11718)

Tags

Sightings

Nomenclature