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Concrete CmsApplication · Concretecms

CVE-2026-8238

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_page' 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 Tristan Madani 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

The '/ccm/frontend/conversations/message_page' endpoint in Concrete CMS 9.5.0 and below lacks proper authorization validation, allowing unauthenticated attackers to access any conversation message by manipulating message identifiers. This IDOR vulnerability exposes messages from restricted pages, member-only areas, the moderation queue, and associated file attachments.

MitigationImplement and enforce proper authorization checks ensuring users can only access conversation messages they are explicitly authorized to view, and validate user permissions before returning any message content or attachments.

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. Check Concrete CMS version
    Navigate to the dashboard and view the version number, or check the version file in your installation. Compare against the affected range of versions below 9.5.1.
    Affected if The installed version is lower than 9.5.1
  2. Verify conversations feature is enabled
    Check if the conversations module is active by logging into the CMS dashboard and looking for conversation-related settings, or inspect the database for active conversation configurations.
    Affected if Conversations are enabled and the CMS version is vulnerable
  3. Test unauthenticated access to the message_page endpoint
    Send a request to /ccm/frontend/conversations/message_page with a message ID parameter (for example, ?messageID=1) without providing any authentication credentials. Observe whether the message content is returned.
    Affected if The endpoint returns message content to unauthenticated users
  4. Check if message IDs can be enumerated
    Submit multiple requests to the message_page endpoint with different message ID values while unauthenticated. Verify whether an attacker can access messages from restricted pages, member areas, or the moderation queue by incrementing the ID.
    Affected if Different message IDs return sensitive content from protected areas without authorization

You are affected if your Concrete CMS version is below 9.5.1 and the conversations feature is enabled, allowing unauthenticated access to the message_page 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

Implement and enforce proper authorization checks ensuring users can only access conversation messages they are explicitly authorized to view, and validate user permissions before returning any message content or attachments.

Recommended fix High confidence

Concrete CMS 9.5.1

  1. 1. Back up your Concrete CMS database and files before upgrading.
  2. 2. Download Concrete CMS version 9.5.1 or later from the official Concrete CMS website (concretecms.com).
  3. 3. Follow the standard Concrete CMS upgrade process: upload the new files, then run /ccm/setup or use the dashboard upgrade wizard.
  4. 4. After upgrade, verify the '/ccm/frontend/conversations/message_page' endpoint no longer returns unauthorized conversation messages.

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

Fix this in Concrete Cms Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing6.0 h
  • Review / QA3.0 h
18.0 hours of engineering $3,120
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,992.

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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-2026-8238 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
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  • No spam, self-promotion, credentials, or personal data