Concrete CMS up to 9.5.3 Custom-Slot Preview Endpoint privileges management

Summaryinfo

A vulnerability was found in Concrete CMS up to 9.5.3. It has been rated as problematic. This vulnerability affects unknown code of the component Custom-Slot Preview Endpoint. Performing a manipulation results in privileges management. This vulnerability is known as CVE-2026-87028. Remote exploitation of the attack is possible. No exploit is available.

Detailsinfo

A vulnerability classified as problematic has been found in Concrete CMS up to 9.5.3. This affects an unknown function of the component Custom-Slot Preview Endpoint. The manipulation with an unknown input leads to a privileges management vulnerability. CWE is classifying the issue as CWE-269. The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor. This is going to have an impact on confidentiality. The summary by CVE is:

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.

It is possible to read the advisory at documentation.concretecms.org. This vulnerability is uniquely identified as CVE-2026-87028 since 09/08/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 09/16/2026). The attack technique deployed by this issue is T1068 according to MITRE ATT&CK.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Type

• Content Management System

Name

• Concrete CMS

Version

• 9.5.0
• 9.5.1
• 9.5.2
• 9.5.3

License

• open-source

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