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Concrete CMS CVE-2026-8204

| EUVD-2026-31348 MEDIUM
Authorization Bypass Through User-Controlled Key (CWE-639)
2026-05-21 ff5b8ace-8b95-4078-9743-eac1ca5451de GHSA-x2fp-hj8c-mmxh
Authentication Bypass
6.3
CVSS 4.0
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CVSS VectorNVD

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

1
Analysis Generated
May 21, 2026 - 21:39 vuln.today

DescriptionNVD

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.

AnalysisAI

Cross-calendar data disclosure in Concrete CMS 9.5.0 and below exposes private calendar event data to unauthenticated remote attackers via an authorization bypass (CWE-639) in the Calendar Event Frontend Dialog. A publicly accessible calendar block serves as a required pivot point, allowing attackers to reference and retrieve event data from private calendars within the same installation. …

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CVE-2026-8204 vulnerability details – vuln.today
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