Concrete CMS up to 9.5.2 Boards canEditBoardContents collection cross site scripting

Summaryinfo

A vulnerability described as problematic has been identified in Concrete CMS up to 9.5.2. This vulnerability affects the function canEditBoardContents of the component Boards. Executing a manipulation of the argument collection can lead to cross site scripting. This vulnerability is handled as CVE-2026-81911. The attack can be executed remotely. There is not any exploit available.

Detailsinfo

A vulnerability classified as problematic was found in Concrete CMS up to 9.5.2. This vulnerability affects the function canEditBoardContents of the component Boards. The manipulation of the argument collection with an unknown input leads to a cross site scripting vulnerability. The CWE definition for the vulnerability is CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. As an impact it is known to affect integrity. CVE summarizes:

Concrete CMS versions 9.0.0 to 9.5.2 is vulnerable to Stored XSS in Board Custom Slot dialog. The custom_slot save_template endpoint authorizes the request only against the target board instance (canEditBoardContents()) and then persists the client-supplied selectedTemplateOption[collection] verbatim, rather than rebuilding the content object collection server-side and verifying that each item belongs to the authorized board's data pool. A user with permission to edit the contents of at least one board instance can therefore store a forged summary object whose description field carries a JavaScript-bearing HTML payload. The default summary template renders the description field without output encoding, so the payload executes in the browser of any user who views the affected board slot, including anonymous front-end visitors and dashboard users who preview the resulting rule or block. This can enable session or action takeover and escalation toward an administrator. Concrete CMS versions below 9 do not include the Boards feature and are not affected. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 5.8 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:L/VA:L/SC:N/SI:N/SA:N. Thanks riodrwn for reporting.

The advisory is available at documentation.concretecms.org. This vulnerability was named CVE-2026-81911 since 08/27/2026. The exploitation appears to be easy. The attack can be initiated remotely. Successful exploitation requires user interaction by the victim. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1059.007 by the MITRE ATT&CK project.

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

License

• open-source

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