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Concrete CmsApplication · Concretecms

CVE-2026-8237

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 IDOR. The `/ccm/frontend/conversations/message_detail` endpoint returns the full content of any conversation message. An unauthenticated attacker can enumerate all conversation messages, including messages from restricted pages, member-only areas, and the moderation queue. File attachments with download URLs are also exposed. The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 6.3 with Vector CVSS:4.0/AV:N/AC:L/AT:P/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 · moderate confidence

Concrete CMS contains an IDOR vulnerability in the /ccm/frontend/conversations/message_detail endpoint. The endpoint fails to enforce proper authorization checks, allowing unauthenticated attackers to access any conversation message by enumerating message IDs. This exposes messages from restricted pages, member-only areas, and the moderation queue, including file attachments with their download URLs.

MitigationImplement proper authentication and authorization checks on the message_detail endpoint to verify the requesting user has rights to view the requested message. Additionally, implement rate limiting to prevent enumeration attacks and validate that the user has access to the specific conversation before returning message content.

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. Identify installed Concrete CMS version
    Access the dashboard and navigate to Dashboard > System & Settings > Basics > Site Information to view the version number, or check the application configuration files for the version marker
    Affected if The installed version is 9.5.0 or below (any version prior to 9.5.1)
  2. Confirm conversation feature is enabled
    Navigate to Dashboard > Conversation Settings or inspect the site configuration to verify that the conversation/messaging system is active
    Affected if Conversations are enabled and the site uses the message_detail endpoint functionality
  3. Verify endpoint is accessible without authentication
    Attempt to access /ccm/frontend/conversations/message_detail with a crafted request (for example, adding a message_id parameter) while logged out from the site
    Affected if The endpoint returns message content or file attachment URLs without requiring login or returning a 403/401 authorization error
  4. Check for sensitive conversation data exposure
    If the endpoint responds, attempt to enumerate different message IDs to see if content from restricted areas, member-only conversations, or moderation queues is returned
    Affected if Messages from restricted or private conversation threads are accessible without authorization

The environment is affected if running Concrete CMS version 9.5.0 or below AND the conversation feature is enabled, allowing the vulnerable /ccm/frontend/conversations/message_detail endpoint to return restricted messages to unauthenticated users.

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 proper authentication and authorization checks on the message_detail endpoint to verify the requesting user has rights to view the requested message. Additionally, implement rate limiting to prevent enumeration attacks and validate that the user has access to the specific conversation before returning message content.

Recommended fix High confidence

Concrete CMS 9.5.1

  1. Back up your Concrete CMS database and files before upgrading
  2. Download Concrete CMS version 9.5.1 from the official Concrete CMS website or repository
  3. Review the upgrade instructions in the Concrete CMS documentation for your current version
  4. Upload and install the 9.5.1 files to your server, replacing the existing installation
  5. Run the upgrade process via the browser by accessing your site or via command line
  6. Verify that the /ccm/frontend/conversations/message_detail endpoint now properly enforces authorization
  7. Test that conversation messages from restricted areas are no longer accessible without proper authentication
  8. Confirm file attachment downloads are also properly protected

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

Fix this in Concrete Cms Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,120.

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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-2026-8237 in production — separate from our analysis above.

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What this is

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What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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