High severity · published May 21, 2026
CVE-2026-8421
Concrete CMS 9.5.0 and below is vulnerable to CSRF on install_package() with conditional token bypass leading to RCE
8.8
CVSS
0.2%
EPSS
No
On KEV
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 gave this vulnerability a CVSS v.4.0 score of 7.5 with vector 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. Thanks  https://github.com/maru1009  for reporting.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 6% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
CC
Concrete CMS · Concrete CMS
5.0 through 9.5.0 · source: vendor, NVD
Affected product
CC
Concrete CMS
Concrete CMS
More from Concrete CMS
9.6
CVE-2026-85385
Concrete CMS below 9.5.4 is vulnerable to Stored XSS via User Timezone Field
9.0
CVE-2026-18119
Concrete CMS below 9.5.3 is vulnerable to Stored XSS via unsanitized inline block custom style values
8.8
CVE-2026-8409
Concrete CMS 9 before 9.5.0 is vulnerable to Cross Site Request Forgery (CSRF) at concrete/controllers/dialog/logs/delete
8.8
CVE-2026-8410
Concrete CMS 9 before 9.5.0 is vulnerable to Cross Site Request Forgery (CSRF) at concrete/controllers/dialog/logs/bulk/delete
8.8
CVE-2026-8411
Concrete CMS 9 before 9.5.0 is vulnerable to Cross Site Request Forgery (CSRF) at concrete/controllers/dialog/page/bulk/delete