CVE-2026-8134: Concrete CMS path traversal and RCE in composer form layouts

CVE-2026-8134 · Severity: high · CVSS 7.2 · Published 2026-05-21

Concrete CMS, a content management system used for building and managing websites, is vulnerable to a security flaw that could allow an administrative user to take full control of the server. By exploiting a weakness in how the system handles file paths and uploads, a malicious user with form-editing permissions can execute unauthorized code on the underlying web server. This could lead to a complete compromise of the website, including the theft of sensitive data or a total service outage.

Technologies: Concrete CMS, concrete5/concrete5 (Packagist). Vendors: Concrete CMS, Packagist.

Quick answers

Is CVE-2026-8134 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-8134 being exploited in the wild.
How severe is CVE-2026-8134?
High severity, with a CVSS score of 7.2, published 21 May 2026.
Which products and versions are affected?
Concrete CMS <= 9.5.0, 9.5.0 and below; concrete5/concrete5 (Packagist) < 9.5.1, ECOSYSTEM:introduced=0,fixed=9.5.1.
Is there a fix for CVE-2026-8134?
Yes. concrete5/concrete5 (Packagist): upgrade to 9.5.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-8134 attacked?
It is attacked over the network, in a network appliance.
Am I affected by CVE-2026-8134?
Check whether you run Concrete CMS or concrete5/concrete5 (Packagist) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • concrete5/concrete5 (Packagist): upgrade to 9.5.1 or later
    composer require concrete5/concrete5:^9.5.1

Technical details

Concrete CMS versions 9.5.0 and below contain a relative path traversal vulnerability (CWE-23) within the 'ptComposerFormLayoutSetControlCustomTemplate' field. The application fails to sanitize path traversal sequences when saving page type composer form layouts. An authenticated attacker with administrator-level privileges (specifically composer form editing rights) can exploit this to include arbitrary readable files. Furthermore, because the CMS file uploader performs only extension-based validation, an attacker can upload a PHP payload disguised as an image (e.g., .png) and use the traversal vulnerability to include and execute it, resulting in remote code execution (RCE). This issue is resolved in version 9.5.1.

Affected products

  • Concrete CMS Concrete CMS <= 9.5.0

Identifiers

  • CVE-2026-8134
  • GHSA-645j-cm4x-3xvw

Timeline

  • 2026-05-21: disclosed
  • 2026-05-21: advisory
  • 2026-05-21: patched: Released in version 9.5.1

References

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