CVE-2026-8134CWE-23CWE-434CWE-98

Concrete CMS 9.5.0 and below is vulnerable to Authenticated RCE via Composer customTemplate Path Traversal leading to PHP File Inclusion

Critical · published May 21, 2026

CVSS v4.0
9.4
EPSS
1%
Percentile
65.8
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v4.0
9.4 · CRITICAL
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
EPSS
0.01113 · 65.8th percentile
Weaknesses
CWE-23 · Relative Path Traversal; CWE-434 · Unrestricted Upload of File with Dangerous Type; CWE-98 · Improper Control of Filename for Include/Require Statement in PHP Program ('PHP Remote File Inclusion')
Published
2026-05-21T20:13Z
EPSS history
Timeline
  • 21 MAY 20:13Z
    Concrete CMS 9.5.0 and below is vulnerable to Authenticated RCE via Composer customTemplate Path Traversal leading to PHP File Inclusion
    cvelistv5