CVE-2026-8204

Medium

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.

SeverityMedium

CVSS5.3

Exploit probability—

Product

Concretecms Concrete Cms

PublishedMay 21, 2026

First seenMay 21, 2026

Weakness typeCWE-639Authorization bypass through user-controlled key

How to fix

Update

concretecms concrete_cms9.5.1 or later
concrete5/concrete59.5.1 or later

Vendor advisories

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

Affected products

Product	Affected versions	Fixed in
concretecms concrete_cms	v < 9.5.1	9.5.1
concrete5/concrete5Packagist	v < 9.5.1	9.5.1

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