{"id":"CVE-2026-11718","revision":"ab91043114c840108922730d043d1011","records":[{"revision":"ab91043114c840108922730d043d1011","observedAt":"2026-10-27T06:23:27.268+00:00","statement":{"source":"nvd","id":"CVE-2026-11718","aliases":[],"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":"2026-06-18T14:17:20.19+00:00","modifiedAt":"2026-10-26T11:10:00.157+00:00","affected":[],"metrics":[{"system":"CVSS 4.0 · cve-coordination@google.com · Secondary","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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","score":9.3,"severity":"CRITICAL"},{"system":"CVSS 3.1 · nvd@nist.gov · Primary","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N","score":9.1,"severity":"CRITICAL"}],"references":["https://github.com/googleapis/mcp-toolbox/pull/3360"],"sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-11718","license":"NIST NVD usage terms; underlying source attribution retained","enrichment":{"sourceStatus":"Analyzed","weaknesses":["CWE-287"],"productCriteria":["cpe:2.3:a:google:mcp_toolbox_for_databases:*:*:*:*:*:*:*:*"],"sourceDates":{"published":"2026-06-18T14:17:20.190","lastModified":"2026-10-26T11:10:00.157"},"relatedAdvisories":[],"note":"NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON."},"key":"nvd:CVE-2026-11718","identifiers":["CVE-2026-11718"]},"retained":false,"historicalAffected":[]}],"coverage":[]}