{"cve":"CVE-2026-11718","nvd":{"published":"2026-06-18T14:17:20.190","modified":"2026-10-26T11:10:00.157","status":"Analyzed","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.","cvss_v4":{"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},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N","score":9.1},"cwes":["CWE-287"],"references":["https://github.com/googleapis/mcp-toolbox/pull/3360"],"products":["google:mcp_toolbox_for_databases"],"source":"nvd","synced_at":"2026-10-26T11:33:08.859761529+00:00"},"epss":{"cve":"CVE-2026-11718","score":0.00185,"percentile":0.08004,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-wcpr-6g7x-p44r","url":"https://osv.dev/vulnerability/GHSA-wcpr-6g7x-p44r","summary":"googleapis/mcp-toolbox: authentication bypass vulnerability in the generic opaque token validation path (validateOpaqueToken)","modified":"2026-06-25T23:11:04.641371574Z","packages":[{"ecosystem":"Go","name":"github.com/googleapis/mcp-toolbox","purl":"pkg:golang/github.com/googleapis/mcp-toolbox","ranges":["<1.4.0"],"fixed":["1.4.0"]}]},{"id":"GO-2026-5706","url":"https://osv.dev/vulnerability/GO-2026-5706","summary":"googleapis/mcp-toolbox: authentication bypass vulnerability in the generic opaque token validation path (validateOpaqueToken) in github.com/googleapis/mcp-toolbox","modified":"2026-06-25T23:01:29.657070254Z","packages":[{"ecosystem":"Go","name":"github.com/googleapis/mcp-toolbox","purl":"pkg:golang/github.com/googleapis/mcp-toolbox","ranges":["<1.4.0"],"fixed":["1.4.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}