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Concrete CmsApplication · Concretecms

CVE-2026-8205

MEDIUM · 5.3 CVSS v3.1 Published 2026-05-21
Fix available
A fix is available. Upgrade to after 9.5.0 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 authorization bypass in the Calendar Block since action_get_events does not check canView on the calendar which results in restricted event details being disclosed. 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 lalalala5678 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 has an authorization bypass vulnerability in the Calendar Block where the action_get_events AJAX endpoint fails to enforce the canView permission check, allowing unauthorized users to access restricted calendar event details that should be hidden.

MitigationImplement proper canView permission validation in the action_get_events method within the Calendar Block to ensure only authorized users can retrieve calendar event information.

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:<= 9.5.0

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
    Locate the version number in the dashboard under Dashboard > System & Settings > Basics > Site Information, or check the composer.json file in the web root
    Affected if Version is 9.5.0 or below (any version up to and including 9.5.0)
  2. Verify Calendar Block is in use
    Check if the Calendar Block is installed and used on any page of the website through the Concrete CMS dashboard or by searching for calendar block instances in the database
    Affected if Calendar Block is present and contains events with restricted permissions
  3. Identify restricted calendar events
    Review calendar events in the Calendar Block to determine if any have view permissions restricted to specific users or groups (not public)
    Affected if There are calendar events that require canView permission to access
  4. Test the action_get_events endpoint
    Send a request to the action_get_events endpoint (typically /ccm/system/calendar/block/action_get_events) without authentication or with a low-privilege account to see if restricted event details are returned
    Affected if The endpoint returns restricted calendar event details without enforcing canView permission

If running Concrete CMS version 9.5.0 or below AND using the Calendar Block with restricted events, the authorization bypass allows unauthenticated access to event details that should require canView permission.

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 a release after 9.5.0
Interim mitigation

Implement proper canView permission validation in the action_get_events method within the Calendar Block to ensure only authorized users can retrieve calendar event information.

Recommended fix Moderate confidence

9.5.1 or later (check documentation.concretecms.org for the latest stable release)

  1. 1. Check current Concrete CMS version in the dashboard under 'Dashboard > System & Settings > Basics > Site Name' or via the version.php file
  2. 2. Backup the database and files before upgrading
  3. 3. Download the latest Concrete CMS release from the official repository
  4. 4. Replace core files, ensuring the /application/config/site.php and /application/files directories are preserved
  5. 5. Run /index.php/ccm/system/upgrade or use the web-based upgrade tool
  6. 6. Verify the Calendar Block now properly checks canView permissions before returning event data
Caveat Minor point release upgrade typically has low risk; always backup first

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
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,390
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,224.

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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-2026-8205 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