Quick answers
- Is CVE-2026-87028 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-87028 being exploited in the wild.
- How severe is CVE-2026-87028?
- Medium severity, with a CVSS score of 6.5, published 16 September 2026.
- Which products and versions are affected?
- Concrete CMS 9.0 through 9.5.3.
- Is there a fix for CVE-2026-87028?
- No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
- How is CVE-2026-87028 attacked?
- It is attacked over the network.
- Am I affected by CVE-2026-87028?
- Check whether you run Concrete CMS at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
The custom-slot preview endpoint in Concrete CMS 9.0–9.5.3 fails to validate that a submitted board InstanceItem belongs to the board instance the requesting user is authorized to edit. Additionally, the endpoint does not enforce page-view permissions before returning page-backed summary content. An authenticated user with edit-board-contents permission on one board can submit the identifier of an item from a different board instance to retrieve sensitive summary fields (page title, description) from pages they would otherwise be forbidden to access. The attack requires prior authentication and knowledge of target item identifiers but no user interaction.
Affected products
- Concrete CMS Concrete CMS 9.0 through 9.5.3
Timeline
- 2026-09-16: disclosed: CVE-2026-87028 published