CVE-2026-7886

Description

Concrete CMS 9.5.0 and below is vulnerable to IDOR in AddMessage/UpdateMessage via attachments[] parameter which can lead to file permission bypass. The `AddMessage` and `UpdateMessage` conversation controllers accept user-supplied file attachment IDs and load files directly via `$em->find(File::class, $attachmentID)` without checking per-file permissions (`canViewFile()`). A user who can post in any conversation can reference any file in the CMS file manager by its sequential ID, effectively bypassing the file permission system. If a site truly has private files, the owner should set up a private storage location https://documentation.concretecms.org/user-guide/editors-reference/dashboard/system-and-maintenance/files/file-storage-locations outside of the webroot so that permissions can be checked on view as well. That way, even if an authorized user attaches a file, or otherwise links to it, unauthorized users won't be able to view the file.

How to fix CVE-2026-7886

To remediate CVE-2026-7886, upgrade the affected package to a fixed version below.

• —upgrade to 9.5.1 or later

Is CVE-2026-7886 being exploited?

Low — EPSS is 0.3%, meaning exploitation activity has not been observed at scale.

Affected packages (1)

• from 0, < 9.5.1

CVSS scores

References (3)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2026-7886
• PATCHgithub.com/concretecms/concretecms
• WEBdocumentation.concretecms.org/9-x/developers/introduction/version-history/951-release-notes