Vulnerability Description
Concrete CMS 9.5.0 and below does not validate a CSRF token before processing requests to /dashboard/extend/update/prepare_remote_upgrade/<remoteMPID>. An attacker who controls the remote package returned for a known marketplace item ID can overwrite the package PHP on disk and force its upgrade() method to execute in a single browser navigation. This results in remote code execution as the web server user. In order to be vulnerable, the victim must be passing canInstallPackages, victim site must be connected to the Concrete marketplace; and the attacker controls the package returned for a marketplace item ID already installed on the victim site. 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 Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Concretecms | Concrete Cms | < 9.5.1 |
Related Weaknesses (CWE)
References
FAQ
What is CVE-2026-8426?
CVE-2026-8426 is a vulnerability with a CVSS score of 8.8 (HIGH). Concrete CMS 9.5.0 and below does not validate a CSRF token before processing requests to /dashboard/extend/update/prepare_remote_upgrade/<remoteMPID>. An attacker who controls the remote package retu...
How severe is CVE-2026-8426?
CVE-2026-8426 has been rated HIGH with a CVSS base score of 8.8/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-8426?
Check the references section above for vendor advisories and patch information. Affected products include: Concretecms Concrete Cms.