Concrete CMS is vulnerable to IDOR in AddMessage/UpdateMessage

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

2.3 · CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-7886: 0.29% estimated exploitation activity in the next 30 days; percentile 21.41 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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.

Published by the source

22 May 2026, 00:31 UTC

Last modified by the source

24 Jun 2026, 20:56 UTC

Source last checked

26 Oct 2026, 14:49 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-p8p9-5953-h9jw

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# Patch Next advisory brief: CVE-2026-7886

Advisory: Concrete CMS is vulnerable to IDOR in AddMessage/UpdateMessage
IDs: CVE-2026-7886, GHSA-p8p9-5953-h9jw
Record: https://patchnext.com/advisories/cve-2026-7886 (revision 1, source checked 26 Oct 2026, 14:49 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 2.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: concrete5/concrete5 9.5.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist concrete5/concrete5: affected < 9.5.1; fixed in 9.5.1

## Suggested inspection (read-only)
- Packagist concrete5/concrete5: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on concrete5/concrete5.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-p8p9-5953-h9jw (GitHub-reviewed advisory GHSA-p8p9-5953-h9jw lists affected ranges: Packagist concrete5/concrete5 >=0 <9.5.1)

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