PT-2026-42547 · Unknown · Concrete Cms

Maru1009 · CVE-2026-8421 · Published 2026-05-21 · Updated 2026-05-21

Positive Technologies (AI Summary)

CVSS v3.1

8.8

High

Base vector

AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Name of the Vulnerable Software and Affected Versions Concrete CMS versions prior to 9.5.1

Description A Cross-Site Request Forgery (CSRF) issue exists in the install package() method of the 'concrete/controllers/single page/dashboard/extend/install.php' endpoint. An attacker can force an authenticated administrator with canInstallPackages permissions to install a package if the attacker has already placed a package under DIR PACKAGES/<handle>/. Because the installation process executes the package controller's install() method as the web server user, this can lead to remote code execution.

Recommendations Update to a version newer than 9.5.0. As a temporary workaround, restrict access to the 'concrete/controllers/single page/dashboard/extend/install.php' endpoint or disable the install package() function until the update is applied.

Exploit

Fix

RCE

CSRF

Weakness Enumeration

CWE-352

Related Identifiers

CVE-2026-8421

GHSA-4C8M-6FWX-M7XQ

Affected Products

Concrete Cms

References · 7

• 🔥 https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/8xxx/CVE-2026-8421.json · Exploit
• https://osv.dev/vulnerability/GHSA-4c8m-6fwx-m7xq · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-8421 · Security Note
• https://osv.dev/vulnerability/CVE-2026-8421 · Vendor Advisory
• https://github.com/concretecms/concretecms · Note
• https://t.me/CVEtracker/54555 · Telegram Post
• https://documentation.concretecms.org/9-x/developers/introduction/version-history/951-release-notes · Note