{"id":"CVE-2026-8204","aliases":["GHSA-x2fp-hj8c-mmxh"],"url":"https://o3.security/vulnerability/CVE-2026-8204","summary":"Concrete CMS 9.5.0 and below is vulnerable to Authorization Bypass in the Calendar Event Frontend Dialog","details":"Concrete CMS 9.5.0 and below is vulnerable to authorization Bypass in the Calendar Event Frontend Dialog which can allow cross-calendar data disclosure. A public calendar block can be used as a pivot point to access private calendar data. The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 6.3 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N. Thanks Winston Crooker for reporting.","published":"2026-05-21T20:56:33.018Z","modified":"2026-08-12T03:51:25.104861759Z","cvss":null,"epss":{"score":0.00211,"percentile":0.11687,"asOf":"2026-08-18"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Packagist","name":"concrete5/concrete5","fixedVersion":"9.5.1"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://documentation.concretecms.org/9-x/developers/introduction/version-history/951-release-notes"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/8xxx/CVE-2026-8204.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-8204"},{"type":"PACKAGE","url":"https://github.com/concretecms/concretecms"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:25.104861759Z"}}