Is there a patch available for CVE-2026-6826?

Yes, a patch is available for CVE-2026-6826. Update the affected software to the latest version immediately.

Concrete CMS CVE-2026-6826

Q: What is the CVSS score of CVE-2026-6826?

CVE-2026-6826 has a CVSS 4.0 base score of 6.9 (Medium). CVSS vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. EPSS exploitation probability: 0.0%.

Q: Which versions of Concrete CMS are affected by CVE-2026-6826?

{fID}` lacks a permission check, returning page IDs, URL handles, and full URLs for every page referencing a given file - including pages explicitly restricted by CMS access controls.. A patch is available.

EUVD-2026-31344 MEDIUM

Information Exposure (CWE-200)

2026-05-21 ff5b8ace-8b95-4078-9743-eac1ca5451de

GHSA-4g7q-44qp-cc5c

Information Disclosure Concrete Cms

6.9

CVSS 4.0 · NVD

Severity by source

NVD PRIMARY

6.9 MEDIUM

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Lifecycle Timeline

Analysis Generated

May 21, 2026 - 21:38 vuln.today

DescriptionCVE.org

Concrete CMS 9.5.0 and below is vulnerable to unauthenticated file usage disclosure via missing permission check in the usage controller. Any unauthenticated visitor can request /ccm/system/dialogs/file/usage/{fID} with any file ID and receive a list of every page that references that file, including page IDs, handles, and full URLs. This includes pages that are otherwise restricted by permissions.The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 6.9 with vector CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N. Thanks Eldudareeno for reporting.

AnalysisAI

Unauthenticated file usage disclosure in Concrete CMS 9.5.0 and below exposes internal page structure to any network-accessible visitor without credentials. The usage controller endpoint /ccm/system/dialogs/file/usage/{fID} lacks a permission check, returning page IDs, URL handles, and full URLs for every page referencing a given file - including pages explicitly restricted by CMS access controls. No public exploit identified at time of analysis, but the CVSS:4.0 AV:N/AC:L/AT:N/PR:N/UI:N vector confirms trivial, unauthenticated network exploitation with no complexity barrier.

Technical ContextAI

Concrete CMS is a PHP-based content management system with a file management subsystem that tracks which pages reference uploaded assets. The usage controller provides this mapping to administrators via the dialog endpoint /ccm/system/dialogs/file/usage/{fID}, where {fID} is a numeric file identifier. CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor) identifies the root cause: the controller returns sensitive relational data - page handles, IDs, and full URLs - without verifying whether the requesting party holds any session, role, or permission. Concrete CMS file IDs are typically sequential integers, making enumeration straightforward. The disclosure includes pages that CMS permission rules otherwise hide from unauthenticated users, breaking the site's content access control model at the metadata level.

RemediationAI

Upgrade to Concrete CMS 9.5.1, which addresses this missing permission check per the vendor release notes at https://documentation.concretecms.org/9-x/developers/introduction/version-history/951-release-notes. If immediate patching is not feasible, restrict unauthenticated access to the path /ccm/system/dialogs/file/usage/ at the web server (nginx location block or Apache <Location>) or WAF layer - note this will break the legitimate admin file-usage dialog in the CMS backend, so the restriction should be removed promptly after patching. No other workarounds that preserve full admin functionality have been identified from available data.