CVE-2026-8426
HighCVSS 8.8Exploitation Probability (EPSS)
Low risk7th percentile - higher than 7% of all known CVEs
Summary
Concrete CMS 9.5.0 and below does not validate CSRF tokens for requests to /dashboard/extend/update/prepare_remote_upgrade/<remoteMPID>. An attacker controlling a remote package can overwrite PHP files and force execution of the upgrade() method, leading to remote code execution.
Risk Assessment
A remote attacker could take over the web server if the victim has canInstallPackages permissions and the site is connected to the marketplace.
Recommendation
Update Concrete CMS to a version above 9.5.0 and restrict canInstallPackages permissions.
Other vulnerabilities in Concrete CMS
See all- CVE-2026-10721High
Vulnerability in Concrete CMS below version 9.5.2 allows an unauthenticated attacker to perform PHP object injection via unserialize() calls in Permission, Cache, and Search components. The attack requires a malicious payload to be placed in the database.
- CVE-2026-7888High
Concrete CMS below version 9.5.2 is vulnerable to PHP Object Injection via unserialize() calls in the Workflow, Form block, and File/Set components that lack the allowed_classes restriction. An unauthenticated attacker may trigger arbitrary PHP object instantiation if a malicious serialized payload has been placed in the database.
- CVE-2026-8353Medium
Concrete CMS versions 9.0 to 9.5.0 are vulnerable to Stored XSS via page name in the Atomik theme. A rogue editor can inject arbitrary JavaScript that executes in the context of any authenticated user visiting the affected account pages.
- CVE-2026-8347Medium
Concrete CMS 9.5.0 and below is vulnerable to IDOR + wrong-authorization-level in the Express association Reorder dialog. This can cause Cross-entity state tampering with view-only permission on one entry. To be affected, a website has to be using express and relying on express entity ordering.
- CVE-2026-8340Medium
Concrete CMS version 9.5.0 and below is vulnerable to CSRF via Backend\File::approveVersion. A victim with edit_file_contents permission can be tricked into publishing an attacker-chosen previously-uploaded file version (downgrade or activation of an unpublished version).
- CVE-2026-8435Medium
Concrete CMS 9 before version 9.5.0 is vulnerable to Cross-Site Request Forgery (CSRF) in the approveVersion() controller. An attacker can exploit this vulnerability to perform unauthorized actions on behalf of an administrator.
- CVE-2026-8434High
Concrete CMS 9 before 9.5.0 is vulnerable to Cross-Site Request Forgery (CSRF) at concrete/controllers/backend/file rescanMultiple(). An attacker can trick an administrator into performing unwanted file operations.
- CVE-2026-8433High
Concrete CMS 9 before 9.5.0 is vulnerable to Cross-Site Request Forgery (CSRF) at concrete/controllers/backend/file rescan(). An attacker can trick an administrator into rescanning a file.
- CVE-2026-8432High
Concrete CMS 9 before 9.5.0 is vulnerable to Cross-Site Request Forgery (CSRF) at concrete/controllers/backend/file star(). An attacker can trick an administrator into starring a file.
- CVE-2026-8427High
Concrete CMS 9 before 9.5.0 is vulnerable to CSRF in the removeFavoriteFolder($id) endpoint. An attacker can exploit this to perform unauthorized actions on behalf of the victim.
Original NVD description (English source)
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.