{"id":"GHSA-8fcc-w5hv-4gxv","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.\n\nWhen verifying an unparsed opaque token via an OAuth 2.0 introspection endpoint (RFC 7662), the toolbox decodes the response into an introspectResp struct where the Active field is declared as a pointer to a boolean (*bool). The code only explicitly rejects a token if the response contains a populated active field set to false (if introspectResp.Active != nil && !*introspectResp.Active). If an introspection endpoint responds with a payload that completely omits the mandatory active key, the internal variable remains nil, causing the conditional check to short-circuit. As a result, Toolbox accepts authorization tokens missing the \"active\" field, granting access to protected tools and underlying data sources.","aliases":["CVE-2026-11717","GO-2026-5251"],"modified":"2026-06-25T19:56:23.513946965Z","published":"2026-06-18T15:32:01Z","database_specific":{"severity":"CRITICAL","github_reviewed":true,"github_reviewed_at":"2026-06-19T16:58:21Z","nvd_published_at":"2026-06-18T14:17:20Z","cwe_ids":["CWE-287"]},"references":[{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-11717"},{"type":"WEB","url":"https://github.com/googleapis/mcp-toolbox/pull/3341"},{"type":"PACKAGE","url":"https://github.com/googleapis/mcp-toolbox"}],"affected":[{"package":{"name":"github.com/googleapis/mcp-toolbox","ecosystem":"Go","purl":"pkg:golang/github.com/googleapis/mcp-toolbox"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"1.4.0"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/06/GHSA-8fcc-w5hv-4gxv/GHSA-8fcc-w5hv-4gxv.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","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"}]}