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Concrete CmsApplication · Concretecms

CVE-2026-8434

HIGH · 8.8 CVSS v3.1 Published 2026-05-21
Fix available
A fix is available. Upgrade to 9.5.1 or later.
See remediation →
95/100
Remediation priority · Urgent
Remotely reachable No privileges

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 before 9.5.0 is vulnerable to Cross Site Request Forgery (CSRF) at concrete/controllers/backend/file rescanMultiple(). The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 2.3 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N. Thanks Yonatan Drori (Tenzai) 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 · moderate confidence

Cross Site Request Forgery (CSRF) vulnerability in Concrete CMS 9 before 9.5.0 in the file rescanMultiple() controller endpoint. The vulnerability allows attackers to induce authenticated users to perform unintended file rescanning operations. The CVSS v4.0 score of 2.3 reflects the low integrity impact (only file metadata changes) and requirement for user interaction, though v3.1 scores it higher at 8.8.

MitigationUpgrade Concrete CMS to version 9.5.0 or later. Until then, implement anti-CSRF tokens on the affected endpoint and consider disabling the vulnerable functionality if upgrade is not immediately feasible.

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:>= 9.0.0, < 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
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

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. Check Concrete CMS installed version
    Access the Concrete CMS dashboard and navigate to Dashboard > System & Settings > About, or check the version file in your installation (typically in concrete/version.php or via composer.json). Compare the version number against the affected range.
    Affected if The installed version is 9.0.0 through 9.5.0 (anything >= 9.0.0 and < 9.5.1)
  2. Verify admin authentication is required for the vulnerable endpoint
    Confirm that the rescanMultiple() function in the backend file controller requires an authenticated administrator session to be accessed.
    Affected if The site uses admin accounts and the file manager functionality is accessible to authenticated administrators
  3. Identify if file manager with rescan functionality is enabled
    Check if the File Manager feature is enabled in Concrete CMS by navigating to Dashboard > Files > File Manager or inspecting the file storage configuration in the database.
    Affected if The File Manager is enabled and accessible to administrators
  4. Confirm presence of affected controller file
    Locate the backend controller file containing the rescanMultiple() function in your Concrete CMS installation (typically under concrete/controllers/backend/ or similar path) and verify its existence and version timestamp.
    Affected if The vulnerable rescanMultiple() function exists in the backend controller

You are affected if your Concrete CMS installation version is 9.0.0 through 9.5.0 and administrators have access to the file manager functionality containing the vulnerable rescanMultiple() endpoint.

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

Upgrade Concrete CMS to version 9.5.0 or later. Until then, implement anti-CSRF tokens on the affected endpoint and consider disabling the vulnerable functionality if upgrade is not immediately feasible.

Recommended fix High confidence

Concrete CMS 9.5.1 or later

  1. 1. Back up your Concrete CMS database and files before making any changes
  2. 2. Download Concrete CMS version 9.5.1 or later from the official source (documentation.concretecms.org or concretecms.com)
  3. 3. Extract the new version files and upload them to your server, overwriting the existing installation
  4. 4. Run the database upgrade process by accessing your site - typically this happens automatically on first access after upgrade
  5. 5. Verify the upgrade was successful by logging into the admin dashboard
  6. 6. Test that the file rescanMultiple() functionality works correctly in the backend
Caveat Review the release notes for 9.5.x for any configuration or feature changes that may affect your site

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
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,800.

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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-2026-8434 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