CVE-2026-8204

Concrete CMS 9.5.0 and below is vulnerable to Authorization Bypass in the Calendar Event Frontend Dialog

State: Published
Severity: 6.3 Medium
Published: May 21, 2026
Updated: May 22, 2026
Reserved: May 9, 2026

Description

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.

Scores

CVSS	Score	Vector	Source
4.0	6.3 Medium	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	ConcreteCMS

Weaknesses

CWE-639 Authorization bypass through User-Controlled key

Affected Products

Product	Versions
Concrete CMSConcrete CMS	5 through 9.5.0Affected

References

https://documentation.concretecms.org/9-x/developers/introduction/version-history/951-release-notesrelease-notes

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