{"id":"EUVD-2026-37880","revision":"d88798b9e9a04e74830f34b3bc72733f","records":[{"revision":"d88798b9e9a04e74830f34b3bc72733f","observedAt":"2026-11-05T04:05:13.017+00:00","statement":{"source":"euvd","id":"EUVD-2026-37880","aliases":["CVE-2026-11718","GHSA-wcpr-6g7x-p44r"],"title":"An authentication bypass vulnerability exists in the generic opaque token validation path (validateOpaqueToken) of googleapis/mcp-toolbox.","description":"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 != \"\" && 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.","state":0,"publishedAt":null,"modifiedAt":null,"affected":[],"metrics":[{"system":"EUVD CVSS 4.0","vector":"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","score":9.3,"severity":null}],"references":["https://github.com/googleapis/mcp-toolbox/pull/3360"],"sourceUrl":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-37880","license":"ENISA EUVD · source terms and attribution apply","enrichment":{"sourceStatus":null,"weaknesses":[],"productCriteria":[],"sourceDates":{"datePublished":"Jun 18, 2026, 11:52:42 AM","dateUpdated":"Jun 18, 2026, 1:53:14 PM"},"relatedAdvisories":[],"note":"EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON."},"key":"euvd:EUVD-2026-37880","identifiers":["EUVD-2026-37880","CVE-2026-11718","GHSA-wcpr-6g7x-p44r"]},"retained":false,"historicalAffected":[]}],"coverage":[]}