---
id: CVE-2026-87028
title: >-
  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 befo…
summary: >-
  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 befo…
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N'
cwe:
  - CWE-862
vendor: concretecms
product: concrete_cms
affected:
  - 'concrete_cms >= 9.0.0, < 9.5.3'
patched:
  - concrete_cms 9.5.3
published: '2026-09-16'
updated: '2026-09-21'
sourceUpdated: '2026-09-21T17:51:39.373'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-87028'
references:
  - url: >-
      https://documentation.concretecms.org/developers/introduction/version-history/954-release-notes
    label: ff5b8ace-8b95-4078-9743-eac1ca5451de
tags:
  - nvd
  - cve.org
epss: 0.00375
epssPercentile: 0.28778
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-17T17:33:44.182942Z'
scores:
  nvd: 6.5
  cna: 5.3
ingestedAt: '2026-09-16T16:59:56.550Z'
---

## Overview

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.

## Affected

- `concrete_cms >= 9.0.0, < 9.5.3`

## Remediation

Upgrade past the affected range:

- `concrete_cms 9.5.3`