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Concrete CmsApplication · Concretecms

CVE-2026-6826

MEDIUM · 5.3 CVSS v3.1 Published 2026-05-21
Fix available
A fix is available. Upgrade to 9.5.1 or later.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Concrete CMS 9.5.0 and below lacks proper permission validation in the file usage controller endpoint at /ccm/system/dialogs/file/usage/{fID}. Any unauthenticated attacker can submit arbitrary file IDs to this endpoint and receive a list of all pages referencing those files, including page IDs, handles, and full URLs—regardless of whether those pages have restricted access controls.

MitigationImplement authentication and authorization checks in the usage controller to verify the requesting user has appropriate permissions before disclosing file usage information. Until a patch is available, consider restricting access to the /ccm/system/dialogs/ path via web server configuration.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Concrete CmsApplication
Affected:< 9.5.1

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Determine Concrete CMS installed version
    Log into the dashboard and navigate to Dashboard > System Information > Overview to view the version number, or check the version file in your installation directory if accessible.
    Affected if The installed version is below 9.5.1 (e.g., 9.5.0, 9.4.x, or earlier)
  2. Test unauthenticated access to file usage endpoint
    Using a browser or curl command, visit http://your-site.com/ccm/system/dialogs/file/usage/1 without logging in. Replace '1' with any file ID that may exist on your site.
    Affected if The endpoint returns a successful HTTP response (200) with JSON data containing file usage information, without requiring login credentials
  3. Verify endpoint exposes restricted page information
    Examine the response from the unauthenticated request. Look for page IDs, page handles, or URLs that should not be visible to public users.
    Affected if The response includes file usage data showing references to pages that have restricted permissions or are not publicly accessible
  4. Confirm the endpoint does not redirect to login
    Observe whether accessing the /ccm/system/dialogs/file/usage/{fID} endpoint redirects you to a login page or returns an authentication error.
    Affected if The endpoint remains accessible and returns data without any authentication challenge or redirect

Your environment is affected if you are running Concrete CMS version 9.5.0 or below AND the /ccm/system/dialogs/file/usage/{fID} endpoint is accessible without authentication, exposing file references and page information that should require proper authorization.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 9.5.1 or later
Fixed in 9.5.1
Interim mitigation

Implement authentication and authorization checks in the usage controller to verify the requesting user has appropriate permissions before disclosing file usage information. Until a patch is available, consider restricting access to the /ccm/system/dialogs/ path via web server configuration.

Recommended fix High confidence

9.5.1

  1. Backup your database and files before upgrading
  2. Download Concrete CMS version 9.5.1 or later from the official source
  3. Follow the official Concrete CMS upgrade documentation to apply the update
  4. Verify the upgrade was successful by checking the dashboard version
  5. Test that the /ccm/system/dialogs/file/usage/{fID} endpoint now requires authentication

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Concrete Cms Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,780
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,848.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-6826 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data