Vulnerability · Published May 21, 2026 · Assigned by ConcreteCMS
CVE-2026-8134Concrete CMS 9.5.0 and below is vulnerable to Authenticated RCE via Composer customTemplate Path Traversal leading to PHP File Inclusion
Critical 9.4
In plain English
A critical-severity unrestricted file upload in Concrete CMS from Concrete CMS. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.7% (higher than 55% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Concrete CMS 9.5.0 and below fails to sanitize path traversal sequences in the ptComposerFormLayoutSetControlCustomTemplate field when saving page type composer form layouts. An authenticated rogue administrator with composer form editing rights can exploit this to include arbitrary readable files on the server. Combined with the file uploader's extension-only validation (which permits PHP code in files saved with image extensions like .png), this can result in authenticated remote code execution. The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 9.4 with vector CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H Thanks Yonatan Drori (Tenzai) for reporting.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Packagist | concrete5/concrete5 | 9.5.1 | GHSA-645j-cm4x-3xvw |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Concrete CMS | Concrete CMS | 5.0 – through 9.5.0 |
Weakness: CWE-98, CWE-434, CWE-23 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H