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Concrete CMS EUVDEUVD-2026-80881

| CVE-2026-87028 MEDIUM
Missing Authorization (CWE-862)
2026-09-16 ConcreteCMS GHSA-3qqv-7xrx-4vm6
Authentication Bypass Concrete Cms
5.3
CVSS 4.0 · Vendor: ConcreteCMS
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Severity by source

Vendor (ConcreteCMS) PRIMARY
5.3 MEDIUM
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/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
vuln.today AI
4.3 MEDIUM

Authenticated user with board-edit permission (PR:L) over the network (AV:N/AC:L) leaks only page title/description metadata, so C:L and I:N/A:N.

3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
4.0 AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (ConcreteCMS).

CVSS VectorVendor: ConcreteCMS

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
X

Lifecycle Timeline

1
Analysis Generated
Sep 16, 2026 - 17:28 vuln.today

DescriptionCVE.org

Concrete CMS 9 through 9.5.3 did not confirm that a board InstanceItem submitted to the custom-slot preview endpoint belonged to the board instance the requesting user was authorized to edit, and did not enforce page-view permission before generating page-backed summary content. As a result, an authenticated user holding edit-board-contents permission on a single board instance could submit the identifier of an item belonging to a different board instance and receive summary fields, including the page title and description, of an underlying page the same user was otherwise forbidden to view. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 5.3 with vector CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N. Thanks Pakung for reporting.

AnalysisAI

Broken authorization in Concrete CMS 9 through 9.5.3 allows an authenticated user who already holds edit-board-contents permission on one board instance to query the custom-slot preview endpoint with an InstanceItem identifier belonging to a different board instance, causing the system to return summary fields - including the underlying page title and description - for pages that user is not permitted to view. The endpoint fails both to validate that the submitted item belongs to a board the requester is authorized to edit and to enforce page-view permission before generating the page-backed summary content. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

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Vulnerability AssessmentAI

Exploitation Requires an authenticated Concrete CMS account (versions 9 through 9.5.3) that already holds edit-board-contents permission on at least one board instance; the attacker then targets the custom-slot preview endpoint with an InstanceItem identifier belonging to a board instance they do not control. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment This is a low-to-moderate severity broken-authorization (IDOR-style) information-disclosure flaw, not a high-priority issue. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation Upgrade to Concrete CMS 9.5.4 or later - the vendor release-notes page for 9.5.4 (https://documentation.concretecms.org/developers/introduction/version-history/954-release-notes) documents the fix, and this is the primary and recommended remediation. … Detailed patch versions, workarounds, and compensating controls in full report.
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EUVD-2026-80881 vulnerability details – vuln.today
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