CVE-2026-8421
Concrete CMS contains a CSRF vulnerability
Description
Concrete CMS 9.5.0 and below contains a CSRF vulnerability in the install_package() method of concrete/controllers/single_page/dashboard/extend/install.php. An attacker who can cause an authenticated administrator to visit a crafted page, and who has placed or caused a package to be present under DIR_PACKAGES/<handle>/, can force the installation of that package without any CSRF protection. Package installation executes the package controller's install() method as the web server user, enabling remote code execution. In order to be vulnerable, the victim must be passing canInstallPackages. The Concrete CMS security team thanks @maru1009 for reporting this issue.
How to fix CVE-2026-8421
To remediate CVE-2026-8421, upgrade the affected package to a fixed version below.
- —upgrade to 9.5.1 or later
Is CVE-2026-8421 being exploited?
Low — EPSS is 0.2%, meaning exploitation activity has not been observed at scale.
Affected packages (1)
- from 0, < 9.5.1
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 4.0 | — | CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N |